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The Great Diseases A collaborative approach to real world science in the classroom Infectious Disease Neurological Disorders Metabolic Disease Cancer Workbook METABOLIC DISEASE Stephanie Tammen, Berri Jacque and Karina Meiri Table of Contents Metabolic Disease Student Workbook Unit 1: What's in your food? Lesson 1.1 Lesson 1.2 Lesson 1.3 Lesson 1.4 Lesson 1.5-6 4 5 14 23 31 39 Unit 5: How does this knowledge apply to me? 180 Lesson 5.1 181 Lesson 5.2 190 Lesson 5.3 195 Unit 2: How does your body use food? Lesson 2.1 Lesson 2.2 Lesson 2.3 Lesson 2.4 Lesson 2.5 61 62 72 82 90 99 Unit 3: What is metabolic disease? Lesson 3.1 Lesson 3.2 Lesson 3.3 Lesson 3.4 Lesson 3.5 Lesson 3.6 106 107 115 122 129 135 141 Unit 4: How do I identify 'good' and 'bad' food? Lesson 4.1-4.2 Lesson 4.3 Lesson 4.4 Lesson 4.5 149 150 157 166 173 2 Welcome to the Metabolic Disease Module! This module has a simple goal – to bring real world science into the classroom! We will learn about biology in a framework that is relevant to our everyday lives. The study of metabolic disease provides this framework because it focuses on how our body responds to food, and how our lifestyle choices change our health. Outline The Metabolic Disease Module has five units, each of which builds upon the others that came before it. The goal of each unit is to answer a new question about food use, and what this means for our health. ■■ Unit 1: What’s in your food? ■■ Unit 2: How does your body use food? ■■ Unit 3: What is metabolic disease? ■■ Unit 4: How do I identify ‘good’ and ‘bad’ food? ■■ Unit 5: How does this knowledge apply to me? 3 Unit 1: Where are we heading? Unit 1: What’s in your food? Unit 2: How does your body use food? Unit 1: Introduction Unit 3: What is metabolic disease? Unit 4: How do I identify ‘good’ and ‘bad’ food? Unit 5: How does this knowledge apply to me? ______________________________________ In this unit we will begin to understand what food is, and what happens to food before it lands on our plates. We will begin the unit by examining the industrial food chain and learning about the additives in food and what they’re for – are additives necessarily bad? We will then investigate the concept of nutritive value and the different components of food and what they’re for. 4 LESSON 1.1 WORKBOOK What does 'food' mean? DEFINITIONS OF TERMS Nutrient — A substance in food that provides nourishment for growth and maintenance of essential biological functions. For a complete list of defined terms, see the Glossary. We all have some idea of what food is, and we all have opinions about ‘good’ food and ‘bad’ food. But where do these opinions come from and are they justified by evidence? In this module we will look at how our perceptions of food can be manipulated by the media, and begin to explore the questions: What is food, and what makes food healthy? We will look more closely at the actual constituents of processed and unprocessed foods, and explore which of them actually impact our health. At the end of this module you will be able to evaluate nutritional claims and make your own choices about what foods are good or bad. What is food? In our lifetimes we will eat about 60 tons of food served at 70,000 meals and countless snacks. We are hard wired to eat when we are hungry, but have also developed the need to eat when we are bored, sitting in front of a television or gathering in social situations. Eating has become so intertwined with culture that when we think about other regions of the globe, one of the first things that comes to mind is ‘what is the food like?’ At first glance, defining food may seem straightforward, but what we consider food could be taboo to others, and some may say that we eat things that are not food! Does being edible make something food? Wo r k b o o k Lesson 1.1 Is a medication food? We can ingest many things but is there a difference between being edible and being food? Typically, food is considered something we eat that provides us with energy and nutrients. Energy from food is used to complete all bodily functions, from maintaining cellular structures to running and reading like you are doing now. Nutrients are substances that are essential to our health that our ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 5 LESSON READINGS bodies cannot sufficiently make on its own. To be considered an essential nutrient a substance must have these characteristics: ■■ It must have a specific biological function (ex: dietary iron is used to carry oxygen on red blood cells) ■■ Removing it from the diet would lead to a decline in biological function (ex: iron-deficient anemia, or the lack of red blood cell function) ■■ Replacing that nutrient before permanent damage occurs must be able to restore that normal biological function (ex: The cure for iron-deficient anemia? Eat iron!) DEFINITIONS OF TERMS Calorie — A unit of heat energy. 1 Calorie = 1,000 calories = 1 kilocalorie. For a complete list of defined terms, see the Glossary. If we use this set of criteria we can define six classes of essential nutrients that we obtain from eating food: carbohydrates, lipids, proteins, vitamins, minerals and water. Later in this module we will examine each of these essential nutrients in more detail. You may already be able to list some food sources rich in these nutrients, in this course we will also explore the functions of nutrients in the body and how much of each nutrient you need to keep your body running smoothly. In addition to maintaining specific biological functions, eating food also provides us with another important thing: energy. For example, carbohydrates, lipids and proteins from food are used to deliver energy to our cells. This energy is commonly called calories. Everybody has a minimal number of calories they need to eat to maintain their health, depending on their age, gender, height, weight and Figure 1: 'Eating the rainbow', physical activity. Without food to supply calories to us, cells or eating foods of many different inside of your body can no longer function, and organ systems colors, is a good way to ensure begin to shut down. We will learn more about what happens that you are consuming all of the essential vitamins and minerals. inside of your body in periods of prolonged fasting, as well as feasting, later in the module. Food is more than a set of essential nutrients If there were a food product that contained the perfect amount of each nutrient, would you want to eat it three meals a day? Many science fiction novels and films have imagined a future where this is true: humans would no longer “waste” their time growing, preparing and eating meals. But in saving this time what sort of customs or traditions would be lost? Wo r k b o o k Lesson 1.1 Think about your favorite foods, and ask yourself: Why is this food so good? Is it the flavors, the smells, or the look of the food? Or do you associate a good memory with eating that food? Everybody has their own personal connection to food, a connection that shapes the flavors that we like or dislike. 1. Essential nutrients are: aa. In everything edible. bb. Needed by the body and made by the body. cc. Needed by the body and must be eaten. dd. All of the above. 2. The number of calories in food tells us: aa. The amount of fat in food. bb. The amount of energy in food. cc. How much you can eat. dd. If the food is healthy. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 6 LESSON READINGS How does food get to our table? The agricultural industry in America DEFINITIONS OF TERMS Food shed — An area of land including where food is produced, transported to, and consumed. Vector — An organism that transmits a disease or parasite from one animal or plant to another. Pesticide — A substance used to destroy insects harmful to crops. For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 1.1 Farming and the cultivation of crops allowed our early ancestors to give up their nomadic lifestyle and begin settling in villages. Up until the early 20th century, most farms were family owned and operated, and were much smaller than they are today. Food sheds, or regional food systems, were also much smaller. For example, if you lived in New England during this time, you would rarely, if ever, find fresh citrus on your table because it does not grow that far north. Instead, you would rely on crops that were being grown in your local area to provide you with all of your nutrients. One of the impacts of the Second World War was a change in the food system in America that led to the national and international food exchange that we have today. Many technologies that were developed for the war effort began to trickle into the agricultural industry. For example, DDT is a chemical that was used to prevent the spread of infectious diseases like malaria and typhus by killing insect vectors like mosquitos and fleas. A major limitation in farming is insect damage to crops, Produc'on which limits food output and contributes to food shortages. After the war, farmProcessing ers began using DDT on their crops as a pesticide to kill the crop damaging insects. Industrial farming equipment also became more commonplace after the war, and small farms were able to use tractors to increase their food yield while employing fewer farm workers. Since then, the number of farms in America has dropped remarkably, and it is increasingly difficult to find true family farms that are not run by a large corporation. Distribu'on Retail Consumers Figure 2: Food goes through many steps to get from the farm to your plate. Food will be processed, repackaged and given additives to increase shelf life and make it more easily transportable. Major upsides of industrialized food The industrialization of agriculture in the United States has led to increased product yield, which in turn keeps the price of food relatively low to consumers. For example, from 1970 to 1995 the yield of wheat and rice nearly doubled, and most industrial countries achieved sustained food surpluses for the first time, 3. Pesticides: aa. Increase crop production. bb. Decrease insect damage to crops. cc. Decrease the cost of food. dd. All of the above. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 7 LESSON READINGS 4. Which is true of our food system today? aa. We have a primarily local food shed. bb. We can always tell where our food is from. cc. The food in the grocery store is from all corners of the world. rather than going through periods of famine. However these measures come with negative consequences, including breaches in food safety and devastating environmental impacts. DEFINITIONS OF TERMS Nutritive value — A measure of the contribution of a food to the overall nutrient content of a diet. Foods with a lot of vitamins and minerals will have a higher nutritive value. We no longer have a regional food system, as food is shipped from all corners of the globe. To witness this, take a walk through the produce section of the grocery store and read where the fruits and vegetables are coming from. There’s a good chance that your fruits and vegetables are coming from parts of the world that you will never personally travel to. This global approach to food supply allows us to have fresh produce year round, but it increases greenhouse gases from transporting the food, and may decrease the nutritive value of the foods that we eat. Food processing, for better or worse For a complete list of defined terms, see the Glossary. Figure 4: An advertisement for Campbell’s soup targeting wives and mothers, promising easy dinners. Wo r k b o o k Lesson 1.1 Figure 3: Industrialized food allows you to get fresh vegetables all year round. While we may think of processed foods as a relatively new invention, evidence of preserving foods through drying, fermentation, cooking or curing with salt exists in Greek, Egyptian and Roman writings. Today’s processed foods are undoubtedly different than our ancestors’, although we still use some of the same methods for food preservation. Like the changes made to growing food discussed above, many of the modern food processing technologies were developed to serve military needs. The process of canning food derived from a vacuum bottling technique developed in 1809 to preserve food shipped long distances to French troops. Later, Louis Pasteur proved that heat killed bacteria, and in 1862 pasteurization was discovered, establishing a protocol in which food could be made microbiologically safe for storage, a process still used today for canned foods. In the 20th century, both World War II and the space race contributed technologies that were adapted to food processing. Advances such as juice concentrates, freezedrying, and the introduction of artificial sweeteners, coloring agents, and preservatives increased the shelf life and diversity of foods that could be processed. Indeed, this processing reduces food waste by preventing spoilage and making foods more suitable for transport around the globe. 5. Food processing: aa. Increases food shelf life. bb. Decreases food waste. cc. Prevents food shortages. dd. All of the above. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 8 LESSON READINGS In Western Europe and North America, the second half of the 20th century gave rise to convenience foods. Food processing companies targeted their products towards middle-class working wives and mothers like in the advertisement on the previous page (Figure 4). Frozen foods and TV dinners were sold as ‘time savers’. This era of quick and easy foods is still where we find ourselves today. DEFINITIONS OF TERMS Food additive — A chemical, or chemicals, added to food to improve its flavor, appearance or shelf life. Food contaminant — Harmful chemicals or microorganisms that unintentionally occur in food from growing or processing. For a complete list of defined terms, see the Glossary. In modern times, the process of getting food to the table is so complex that we sometimes question whether we can still call some of these products “food”. Nonetheless, food processing has advantages. Vitamins and minerals are often added to certain food products to increase their nutritive value, bringing these essential nutrients to populations without year-round access to fresh fruits and vegetables. Figure 5: Processed convenience foods have become a larger part of our diets in the 20th century. In the next two lessons we will learn more about items that are added to food intentionally or unintentionally. Chemicals called additives are added to food to improve taste, nutritional quality or shelf life. Because food processing typically uses large mixing, grinding, chopping and emulsifying equipment, other chemicals or microbes can inadvertently get into the food, called contaminants. Striking a balance: Why is our diet important? The types of nutrients that we consume can have a lasting effect on our health. Even more, food impacts health not only through what we eat, but also how much we eat. Both the under consumption and overconsumption of food can lead to negative health outcomes. In developed countries like the United States, calorie rich food is abundant and relatively cheap, so it makes it easy to over-consume food. Because of this, the U.S. has led the globe in rates of people that are either overweight or obese. Figure 6: Eating too little, or too much food can lead to health problems or in some cases, death. Micronutrient deficiencies Wo r k b o o k Lesson 1.1 Micronutrient deficiencies arise from eating too little of a particular vitamin or mineral. Some common micronutrient deficiencies in the United States include iron, calcium, vitamin B12 (especially in people who are vegetarian or vegan) and iodine. Your risk for having a particular micronutrient deficiency depends ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 9 LESSON READINGS upon your age, gender, and your access to fresh healthy foods. Around the world micronutrient deficiencies are associated with poverty and insufficient intake of a balanced diet, and we often imagine a person that is starving when we think of someone with a micronutrient deficiency. A new trend is emerging however, in which people who are overweight or obese also have one or more micronutrient deficiencies. Consuming a diet high in calories, but low in nutritive value, causes this new phenomenon. Metabolic Syndrome DEFINITIONS OF TERMS HDL — A type of lipid-carrying protein in the blood that protects against cardiovascular disease by removing cholesterol from arteries or tissues. Metabolic Syndrome — A combination of medical disorders that, when occurring together, increases the risk of developing cardiovascular disease and diabetes. Triglyceride — The main constituent of natural fats and oils. High levels in the blood indicate a high risk for cardiovascular disease. For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 1.1 With the rise of obesity in the U.S., there has been a subsequent rise of people going to their doctors with a common set of symptoms that have been lumped together and called Syndrome X, or Metabolic Syndrome. There are five classic symptoms or signs of Metabolic Syndrome that physicians will use for diagnosis: ■■ Large waist circumference, demonstrating central obesity – Carrying a lot of weight in the middle portion of your body is associated with poor health outcomes. This body type is often called ‘apple-shaped’ shown to the right. Figure 7: Five symptoms of Metabolic Syndrome. ■■ Elevated blood pressure, also called hypertension – Increased blood pressure is the result of the heart or kidneys not properly functioning. ■■ High blood triglyceride concentrations – A measure of how much fat is in the blood. A diet high in fat or sugar can lead to increased triglyceride concentrations. ■■ Low blood HDL (‘good’) cholesterol concentrations – HDL cholesterol is responsible for removing extra fat from the tissues, so low levels are indicative of an excess of fat in the tissues and blood. ■■ High fasting blood glucose concentration, also called insulin resistance – The liver and the pancreas tightly regulates blood glucose (or sugar in the blood) concentrations. In type 2 diabetes the pancreas no longer functions normally and fasting blood glucose levels rise. While these symptoms are characteristic of Metabolic Syndrome, obesity is closely linked to other diseases like heart disease and type 2 diabetes, both of which are chronic diseases requiring long-term use of prescription drugs and lifestyle changes to overcome. Unfortunately these diseases used to be only diagnosed in older adults, but because obesity is affecting younger populations there is a rise in early onset of heart disease and type 2 diabetes. We will learn more about these metabolic diseases in greater detail in Unit 3. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 10 STUDENT RESPONSES Give a brief argument both for and against the statement “a candy bar should be considered food”. _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ ____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ Wo r k b o o k Lesson 1.1 _____________________________________________________________________________________________________ ___________________________________________________________________________________________ 11 TERMS TERM For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 1.1 DEFINITION Calorie A unit of heat energy. 1 Calorie = 1,000 calories = 1 kilocalorie. Carbohydrates A large group of compounds occurring in foods, including sugars, starches and fiber. Found in grains, produce, desserts and sweet beverages. Fasting A period of time when no food is consumed. Feasting A period of time when food is consumed, such as during a meal. Food Additive A chemical, or chemicals, added to food to improve its flavor, appearance or shelf life. Food Contaminant Harmful chemicals or microorganisms that unintentionally occur in food from growing or processing. Food Shed An area of land including where food is produced, transported to, and consumed. HDL A type of lipid-carrying protein in the blood that protects against cardiovascular disease by removing choles terol from arteries or tissues. Lipids A class of compounds called fatty acids, including oils and solid fats. Metabolic Syndrome A combination of medical disorders that, when occurring together, increases the risk of developing cardio vascular disease and diabetes. Minerals Basic elements that are required for biological reactions. Nutrient A substance in food that provides nourishment for growth and maintenance of essential biological functions. Nutritive Value A measure of the contribution of a food to the overall nutrient content of a diet. Foods with a lot of vitamins and minerals will have a higher nutritive value. Pesticide A substance used to destroy insects harmful to crops. Proteins A class of compounds consisting of one or more amino acid. Found in legumes, meats and eggs. Triglyceride The main constituent of natural fats and oils. High levels in the blood indicate a high risk for cardiovascular disease. 12 TERMS TERM DEFINITION Vector An organism that transmits a disease or parasite from one animal or plant to another. Vitamins Compounds that cannot be synthesized by the body but are required for biological reactions. For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 1.1 13 LESSON 1.2 WORKBOOK What's in your food besides food? DEFINITIONS OF TERMS Food additive — A chemical, or chemicals, added to food to improve it flavor, appearance or shelf life. GMO — Genetically modified organism . An organism in which the genetic material has been altered in a way that does not occur in nature. In the previous lesson we described the characteristics of what makes something food, and learned about some differences between processed and whole foods. In this lesson we will discuss ‘things’ that make it into your food that don’t add any nutritional value. This includes some of the major food additives, pesticides, antibiotics, hormones and GMO foods. You will learn why additives are used and debate their pros and cons. For example, additives can preserve food, reducing food waste and food cost, but they may also negatively impact our health and the environment. The purpose of intentional food additives For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 1.2 Figure 1: Food additives have four main purposes. The introduction of many additives into our food occurred alongside our modern day adoption of food processing. The act of processing foods can sometimes alter the taste and texture of foods, or decrease the amount of beneficial nutrients in the end product. Intentional food additives are mainly used to make the food more palatable or enticing to us, to increase the shelf life of food, and to add essential nutrients (see the figure on the left). You can identify intentional food additives because they will be listed under the ingredients on the Nutrition Facts panel. Below we will discuss some commonly used intentional food additives. 1. Intentional food additives are used for all of the following except: aa. To make our food more transportable over long distances. bb. To make our food taste better. cc. To make our food grow faster. dd. To make our food safer to eat. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 14 LESSON READINGS Additives can increase the tangible aspects of foods DEFINITIONS OF TERMS Bran — A portion of the wheat kernel that contains B vitamins and fiber. The bran is included in whole wheat fiber. Endosperm — A large portion of the wheat kernel that is used to produce white flour. The endosperm contains most of the protein and carbohydrates in wheat. Food preservative — A substance added to a food product to prevent spoiling, either by preventing microbial growth, oxidation, or early ripening. Germ — A small portion of the wheat kernel that is the sprouting section of the seed. The germ contains B vitamins and is included in whole wheat flour. For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 1.2 The tangible aspects of food are those parts that we can quantify: crop yield, shelf life and nutritive value. One major class of additives is food preservatives. Some common food preservatives that you may see on a food label are EDTA, sodium benzoate and citric acid. By using food preservatives, less food spoils before it gets to us, preventing food waste. Before grocery stores and restaurants were commonplace people grew and preserved most of their own food, and food rarely traveled far distances. These days, we rely on farmers and food manufacturers to bring food to us, meaning food has to travel longer distances and be stored in warehouses and trucks on the way to our kitchens. This would not be possible without the invention of additives to preserve food. In general, food preservatives can be grouped into three categories: 1. Preventing bacterial or fungal growth – These preservatives work by inhibiting the growth of microbes. For example, sodium benzoate is added to acidic, water containing foods like sodas or pickles, and creates an environment where bacteria and yeast cannot grow. 2. Protecting the food from oxidation – Antioxidants are used to stop the chemical breakdown of food that happens when the food is exposed to air. Oxidation is why cut apples turn brown. The same antioxidants will often times work both inside and outside of our bodies, like those we get from our diet: Vitamin C (ascorbic acid) and Vitamin E (tocopherols). 3. Preventing fruits and vegetables from ripening too quickly – Enzymes in produce that cause ripening can be stopped by changing the pH of the food. Acids like citric acid or ascorbic acid are often added to foods for this purpose. Nutrients are sometimes added to a food product to make them healthier. When some foods are processed they lose nutritional value, so food companies will add key nutrients back into the food. Consider the steps involved in turning wheat into flour: after being harvested, the fibrous bran and a nutritious part of the wheat grain called the germ is removed, leaving only the endosperm to be ground down into flour (Figure 2). This flour is sometimes bleached to give light, white fluffy flour you may use to bake cookies or cakes, causing further loss of vitamins, minerals and fiber. Because wheat flour is highly consumed, in 1996 the U.S. government mandated the addition of iron and the B vitamins folic acid, riboflavin, thiamin and niacin to all non-organic wheat flour. This allowed the food processors to continue to make their product without putting the U.S. population at risk for nutrient deficiencies. Other examples of food fortification are the addition of vitamin D to milk and iodine to salt. Bran! Endosperm! Germ! Figure 2: During wheat processing, the germ and bran are removed, and the endosperm is ground down into flour. 2. Some food additives make us healthier: aa. True. bb. False. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 15 LESSON READINGS Some additives can increase the non-tangible aspects of foods: color, flavor and texture Color DEFINITIONS OF TERMS Cardiovascular disease — Also called heart disease. A disease of the heart or blood vessels. Hypertension — Abnormally high blood pressure. For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 1.2 The non-tangible aspects of food are those characteristics that we can sense, like the look, taste or texture. For example, food colorings make food look more appetizing without altering the flavor. Imagine the colors of some of your favorite processed foods: bright orange cheese flavored chips, colorful candies, green mint flavored ice cream, chances are these foods get their colors from chemical food coloring. Synthetic food colors are created in a laboratory and have names like Yellow #5, whereas natural food colors are derived from plants, like beet juice or turmeric. Figure 3: Food additives can be used to create a more appealing color that mimics freshness. Flavor Flavor enhancers like sugar, salt and monosodium glutamate (MSG) are added so you enjoy the food you’re eating, and to make you want more! Imagine eating potato chips with no added salt, flavors (like nacho cheese, or ranch flavoring) or MSG– you would probably get bored of eating them pretty quickly. Salt and MSG are called flavor enhancers because they make other flavors taste better. This means that even if you are eating something that you don’t consider salty, food manufacturers may still include salt or MSG in the final product to make it taste better. In the United States, most of our dietary salt intake comes form eating highly processed foods, which has been linked to hypertension and cardiovascular disease. You can determine if there is a lot of salt in your food by looking at the Sodium content on the Nutrition Facts panel. Figure 4: Common sources of added sugars in the American diet. Soda, energy and sports drinks are a top contributor. Sugar is often added to processed foods to make them sweeter, but identifying if your food has any added sugars can sometimes be tricky because sugar has so many names. For example, sugar is glucose, sucrose, maltose, fructose, cane sugar, corn syrup and high fructose corn syrup. These can all be found in the ingredients of processed foods, and they are all added sugars. Additionally, non-caloric sweeteners like aspartame, sucralose or stevia have become popular food additives because they have the benefit of making a food sweeter without adding calories. Because added sugars offer calories with no helpful vitamins or minerals, 3. How would a macaroni and cheese pasta meal prepared without any additives compare to a boxed version with additives? They would: aa. Taste the same. bb. Look the same. cc. Have a similar number of calories. dd. Have the same shelf life. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 16 LESSON READINGS it is recommended that we limit eating calories from added sugars to 100 calories a day for women, and 150 calories a day for men. Texture DEFINITIONS OF TERMS Emulsifiers — A substance that stabilizes a blend of fats and water. Pasteurization — Heating a food or beverage to a specific temperature for a set length of time to kill harmful microorganisms. Pesticide — A substance used to destroy insects harmful to crops. Stabilizers — A substance that prevents or inhibits a chemical reaction, usually added to maintain a certain texture. Thickeners — A substance added to a liquid to make it firmer. Viscosity — A measure of fluidity or stickiness. Honey or pudding is more viscous than water. For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 1.2 Figure 5: Gelatin is often added to thicken foods. The last types of intentional food additives are those that alter the texture or viscosity of foods, like emulsifiers, thickeners and stabilizers. You may recognize these additives on your food labels as gums, gelatins, pectins or lectins. These additives can help to maintain the structure and physical properties of food products, which is important when it is going to undergo freezing or high temperatures from canning or pasteurization. When we cook food at home, we don’t usually use the same emulsifiers, thickeners or stabilizers that the food industry uses because we are cooking food in small batches to be consumed quickly. Unintentional food additives Accidental, or unintentional food additives become a part of food through some aspect of production or packaging, and have no function in the final product. These food additives are not listed on the Nutrition Facts panel, therefore the consumer has no real way of knowing whether they are in their food. Some unintentional food additives can also be considered a food contaminant, something that will be discussed more in the next lesson. Increased food production tactics bring new additives GMOs, pesticides and herbicides In an effort to increase crop yield farmers often employ a variety of tactics that may inadvertently introduce food additives into your diet. Through genetic engineering, some seeds have been modified to make them easier to grow or to increase their nutrients or flavor; these are called genetically modified organisms, or GMOs. For example, farmers may use GMO seed varieties that are resistant to pesticides and herbicides, so when the crop is sprayed the GMO plant will survive, but the insects and weeds will die. While this technology has made farming more productive, it has led to more prolific herbicide and pesticide use. Many people are concerned that these chemicals may find their way into the foods that we eat and can negatively affect the environment. Figure 6: Pesticides, like the ones this crop duster is dispersing, can end up in our food. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 17 LESSON READINGS Antibiotics and growth hormones DEFINITIONS OF TERMS Antibiotic — A medicine or chemical that destroys or inhibits the growth of microorganisms. BPA — Bisphenol A. A synthetic compound found in plastics used to store food or beverages. Hormone — A chemical message that is produced by one tissue in the body and transported in the blood to another tissue. For a complete list of defined terms, see the Glossary. New methodologies to enhance livestock growth have also been adopted, including the widespread use of hormone injections and antibiotics in animal feed. Some hormones, like recombinant bovine growth hormone (rBGH) are used to increase the production of milk in dairy cows, while other hormones are used purely to speed up the animals’ weight gain. Although there is no way to measure differences in milk from rBGH treated cows, many people are concerned about potentially harmful impacts on people. Antibiotics are also used to increase the rate of animal growth. While the reason is currently unknown, cattle grow faster when administered a constant low dose of antibiotics, making the practice enticing for the beef industry. Like rBGH, the levels of antibiotics used are very low and measuring differences in the beef treated with antibiotics is challenging. Still, many people are concerned about the unknown, potentially negative impacts on people. For example, the agricultural industry is currently the top user of antibiotics, which has been cited as a contributing factor for the alarming spike in antibiotic resistant bacteria strains. Processing contaminants Once foods are harvested, other production steps may accidentally introduce contaminants into our foods. Plastics and metals from processing equipment or packaging can sometimes leach into the food. For example, BPA is a plastic widely used for bottles and the lining of cans that may disrupt normal hormone signaling in our bodies. Since this discovery, the food industry has decreased its use of BPA in their packaging. Step in Food Production Selection of crops Growth of crops or livestock Processing of food Packaging of food Possible Additive(s) Introduced GMOs Pesticides, herbicides, hormones, antibiotics Food coloring, preservatives, thickeners, stabilizers, nutrients Plastics, heavy metals Figure 7: Summary of intentional and unintentional (in italics) additives can be added to our food at many steps throughout food production. Food additives can be controversial Wo r k b o o k Lesson 1.2 For all of the benefits food additives bring, why not add them to all of our food? Food additives minimize waste and make foods more accessible to regions of the world where food doesn’t easily grow. Unfortunately, not all food additives are safe, and some have even been made illegal after scientists found they 4. Unintential food additives can be used: aa. To make our food more transportable over long distances. bb. To make our food taste better. cc. To make our food grow faster. dd. To make our food safer to eat. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 18 LESSON READINGS were detrimental to human health. Additives may find their way into our food for decades before we realize they are unsafe, mostly because scientists did not have the resources to test safety when the additive was first introduced. For example, most food safety trials are done over a short period of time, and the additive may only have negative health impacts after being consumed over many years. Food additives are GRAS DEFINITIONS OF TERMS FDA — Food and Drug Administration: A federal agency responsible for monitoring trading and safety standard in the food and drug industries. GRAS — Generally Recognized as Safe. A substance that is generally recognized among qualified experts as being shown as safe under the conditions of its intended use. For a complete list of defined terms, see the Glossary. While the additives that are in use today have been deemed by the Food and Drug Administration (FDA) to be Generally Recognized As Safe (GRAS), the safety of every additive has not been thoroughly researched. Although scientific studies are required to test the additive under a limited set of conditions, some additives we use today may be deemed unsafe in the future. This is in part because there is no way to positively test for a lack of negative health impacts. So unless negative impacts arise, the FDA has no scientific evidence against the use of the additive. In essence, the GRAS classification means ‘not proven unsafe’ rather than ‘proven safe’. Figure 8: Food colorings are responsible for making many processed foods an appealing color, but may be detrimental to our health. Additionally, when food additives are being tested for safety they are usually tested alone, without other additives. This is not how we eat additives in a food product, and mixing additives could lead to reactions that create damaging chemicals. Therefore, scientists may determine that a food additive is not unsafe under certain conditions, but can never prove its safety. Because this is the case, the FDA uses the term GRAS. Some food additives are no longer used because of consumer backlash or health concerns. For example the use of DDT, which was one of the original pesticides used after World War II, was found to interfere with normal hormone signaling and might lead to cancer, so its use has been discontinued under most circumstances. Likewise, formaldehyde was once used to preserve foods, but upon the discovery that it is a potent carcinogen, its use in the food industry has ceased. In 1950, the food coloring Orange #1 was banned after several children became sick after eating Halloween candy dyed with the additive. The US allows more food additives than other developed countries Wo r k b o o k Lesson 1.2 Because the FDA requires solid evidence that a substance is unsafe for human consumption before it bans that substance, some additives banned European countries are still used in the United States. For example, some food colorings have been banned in Europe and products containing food dyes in Europe are now required to have a label that warns consumers of an association between artificial food coloring and hyperactivity in children. In addition, many countries have banned the growth or importation of GMO crops, including several European countries, Saudi Arabia, Algeria, Thailand, Sri Lanka, and others. 5. All of the following are challenges the FDA faces in determining the safety of food additives, except: aa. It is difficult to determine what a food additive is. bb. Multiple food additives are often used together in a single food product. cc. The health consequences of an additive over a lifetime cannot be easily studied. dd. It is difficult to prove the lack of an effect of a substance on health. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 19 STUDENT RESPONSES Find a processed food around you to analyze. Look at the Nutrition Facts panel and determine what additives are in the food. What types of unintentional food additives do you think may be in that product? Describe how that food was made, and what steps it went through to get from the farm to you. _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ Remember to identify your sources _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ ____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ Wo r k b o o k Lesson 1.2 _____________________________________________________________________________________________________ ___________________________________________________________________________________________ 20 TERMS TERM For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 1.2 DEFINITION Antibiotic A medicine or chemical that destroys or inhibits the growth of microorganisms. BPA Bisphenol A. A synthetic compound found in plastics used to store food or beverages. Bran A portion of the wheat kernel that contains B vitamins and fiber. The bran is included in whole wheat fiber. Cardiovascular Disease Also called heart disease. A disease of the heart or blood vessels. Emulsifier A substance that stabilizes a blend of fats and water. Endosperm A large portion of the wheat kernel that is used to produce white flour. The endosperm contains most of the protein and carbohydrates in wheat. FDA Food and Drug Administration. A federal agency responsible for monitoring trading and safety standard in the food and drug industries. Food Additive A chemical, or chemicals, added to food to improve it flavor, appearance or shelf life. Food Preservative A substance added to a food product to prevent spoiling, either by preventing microbial growth, oxidation, or early ripening. Germ A small portion of the wheat kernel that is the sprouting section of the seed. The germ contains B vitamins and is included in whole wheat flour GMO Genetically modified organism. An organism in which the genetic material has been altered in a way that does not occur in nature. GRAS Generally Recognized as Safe. A substance that is generally recognized Hormone A chemical message that is produced by one tissue in the body and transported in the blood to another tissue. Hypertension Abnormally high blood pressure. Pasteurization Heating a food or beverage to a specific temperature for a set length of time to kill harmful microorganisms. Pesticide A substance used to destroy insects harmful to crops. 21 TERMS TERM DEFINITION Stabilizer A substance that prevents or inhibits a chemical reaction, usually added to maintain a certain texture. Thickener A substance added to a liquid to make it firmer. Viscosity A measure of fluidity or stickiness. Honey or pudding is more viscous than water. For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 1.2 22 LESSON 1.3 WORKBOOK Food Safety DEFINITIONS OF TERMS Microbe — A microorganism, such as a bacteria or virus, that causes a disease or fermentation. Heavy metal — A metal with relatively high density or a high relative atomic weight. Lead, mercury and cadmium are all heavy metals. For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 1.3 In Lesson 1.2 we identified food additives and investigated their pros and cons; today we will focus on how food can be contaminated by microbes or harmful chemicals. We have seen how vast and complex the process of food production can be. Food can be contaminated with microbes or harmful chemicals at each stage of production: growth, harvest, processing, transport, sales and preparation. In this lesson, real cases of food-borne illnesses will be discussed to illustrate how food contamination can impact our health. How does our food get contaminated? What is the difference between a food additive and a contaminant? Food contaminants are chemicals or microbes that accidentally enter our food system and are harmful to human health. Using this definition, some chemicals can be unintentional food additives and food contaminants. Being a contaminant implies that the chemical or microbe is harmful to your health. Identifying contaminants and their sources can be challenging, and consumers may consider a certain chemical or food additive a contaminant even though it is not officially recognized by the government as a harmful substance. For example, some people believe that eating GMO crops is harmful to their health, even though there hasn’t been enough scientific research to either support or deny this claim You’ve probably had food in your house contaminated by fungus in the form of mold. Food left in the refrigerator, or bread left uneaten is a perfect environment for mold spores. Fortunately, mold is a visibly obvious food contaminant, so we can avoid eating it. Other food contaminants are not so obvious, like bacteria or heavy metal poisoning, and can cause hundreds or thousands of people or pets to get sick before the contaminant is identified. Additionally, even if a contaminant is identified, the complexity of the food production process may make it very hard to find the source. 1. The difference between food additives and contaminants is: aa. Food additives are always added intentionally. bb. Contaminants are always added intentionally. cc. Contaminants are harmful to your health, additives aren’t. dd. They are the same. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 23 LESSON READINGS Contamination of food when it is growing Bacteria and fungi, like mold, require water and a food source to survive. These microbes can come into contact with our food supply in many ways, starting when the food is being grown. Factory farming has led to livestock being raised in close living quarters, which encourages the spread of infectious diseases. Like we learned in Lesson 1.2, livestock may be administered antibiotics to prevent Figure 1: Manure lagoons located the transmission of disease, but some bacteria can next to large feeding facilities have still find their way into the manure of the animals, ideal conditions for microbes to thrive. where the bacteria thrive on the organic matter. In These microbes can contaminate our meat, or even crops growing nearby. large animal feeding facilities the manure is collected in ponds called manure lagoons, like the one on the right (Figure 1), where the waste can be managed before re-entering the water system. Bacteria from these lagoons can be transmitted to other livestock or even onto produce growing nearby through water or wildlife. Some contaminants enter the food supply from the environment. Mercury is abundant in the environment and is converted to the neurotoxin methylmercury by bacteria in water. When consumed by humans, methylmercury can cause nerve damage, fatigue and learning delays. Fish are our primary dietary source or methylmercury. Although we can all tolerate a low amount of methylmercury, children and breast-feeding women are at risk for methylmercury poisoning. To limit exposure, do not eat fish with high levels (swordfish, mackerel and tilefish) and limit your consumption to fish with lower levels (white tuna, shrimp, pollock, salmon and catfish). Wo r k b o o k Lesson 1.3 Figure 2: Heavy metals and minerals are absorbed from soils into the leaves and fruits of plants. Other heavy metals, like lead and cadmium, can contaminate crops through soil. Some regions are prone to having higher metal content in the soil, like former industrial areas. Along with helpful minerals, plants can absorb harmful metals from the soil through their roots, ultimately leading to a crop containing the chemical. Some of these metals are essential to our health, like iron and zinc, while lead, cadmium and arsenic are contaminates. 2. When being grown, foods can be contaminated by: aa. Natural chemicals they absorb from their environment. bb. Microbes they contact in their environment. cc. Chemicals humans have left in their environment. dd. All of the above. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 24 LESSON READINGS Contamination of food as it is preserved, processed or transported During the canning or preservation process microbes can get into the food. While most microbes need oxygen to survive, Clostridium botulinum is a type of bacteria that lives in low oxygen conditions, such as canned food. When consumed, these bacteria can cause vomiting, diarrhea, double vision, muscle weakness and even death. (Interestingly, the same bacteria create the Botulinum toxin that paralyzes muscles, Figure 3: Damaged cans commonly known as Botox®.) If food is processed or transmay contain botulism. ported in an unsterile environment bacteria contamination can occur, and the microbes can live in our food unnoticed until they cause severe illnesses. One example of a common microbial food contaminant introduced during food processing is Listeria. When food processing equipment, like those used to mechanically separate meats, is not cleaned properly the bacteria can get into the food. In fact, Listeria can be found in many deli meats and some soft cheeses. Listeria infection can lead to diarrhea, fever and abdominal cramps. In fact, this is why pregnant women are recommended to avoid eating lunch-meats and soft cheeses. Chemical contamination can also be introduced during food processing. For example, some heavy metals like cadmium, copper, iron, tin and zinc can be consumed by eating foods or beverages that are improperly processed, stored or cooked in containers containing these metals. Typically, food processors will put foods through a metal detector before shipping them off to the consumer, but despite this precaution there is still a risk of heavy metal poisoning from processed foods. Chemical contamination of foods can also occur during food processing. For example, the common preservatives sodium benzoate and ascorbic acid in soft drinks can react to make benzene, a chemical that is a known carcinogen, although the levels of benzene in soda are low. Step in Food Production Growth of crops or livestock Wo r k b o o k Lesson 1.3 Growth of crops or livestock Processing of food Packaging of food Possible Contaminant(s) Introduced Pesticides, herbicides, heavy metals (mercury, lead, cadmium), microbes Microbes Microbes, chemicals (benzene) Heavy metals (copper, tin, zinc), plastics 3. All of the following are common contaminants introduced during food processing and transport, except: aa. Listeria. bb. Salmonella. cc. Mercury. dd. Benzene. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ Figure 4: Common steps in food production where contamination may occur. 25 LESSON READINGS Transportation of food opens up another possibility of contamination. If food is transported in a temperature that promotes microbe growth, bacteria may grow to harmful levels before the food product reaches the consumer. Additionally, large tanks that carry unpasteurized liquids need to be carefully cleaned between shipments. Any error in proper cleaning could lead to growth of pathogenic bacteria. Another common food contaminant introduced when food is growing and being transported is Salmonella. Eating food contaminated with salmonella may lead to diarrhea, fever, abdominal cramps and vomiting. Salmonella may come in contact with the food when contaminated manure is used to fertilize crops or when contaminated shipping containers or ice contact the food. Organism Salmonella Onset after Signs & Symptoms Duration ingesting 6-48 hours Diarrhea, fever, 4-7 days abdominal cramps, vomiting Listeria 3-70 days monocytogenes Methylmercury Varies Diarrhea, fever, abdominal cramps Impaired vision; tingling in hands, feet and around mouth; lack of coordination; muscle weakness 5-10 days Food Sources Eggs, poultry, meat, unpasteurized milk or juice, cheese, contaminated raw fruits and vegetables Milk, soft cheeses, deli meats SympLarge fish, shark toms are irreversible Figure 5: Three common sources of foodborne illness with short description of symptoms. Protecting yourself from contaminated foods The FDA is responsible for maintaining food safety Wo r k b o o k Lesson 1.3 We previously learned that the Food and Drug Administration in the United States regulates what additives can be in our food. The FDA also tests food for contaminants. Unfortunately, the FDA cannot test everything because there is so much food, so instead they take small, random samples in an effort to prevent tainted food products from reaching the consumer. This doesn’t always work, and sometimes food that has a contaminant is eaten, leading to illness. You will see some real cases of microbial and chemical food contamination in Lesson 1.3 and you will try to identify the source and cause of the illness. 4. The FDA tests all food for contamination: aa. True. bb. False. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 26 LESSON READINGS Tracing food contamination is challenging Food production is an international business, food from one farm can be shipped all over the world, leading to a worldwide outbreak of the foodborne illness. Who is to blame for this contamination? It is often very difficult to determine where in the food production process the contaminant was introduced. Can we ask farmers to prove that their food isn’t contaminated? How about the food manufacturers? These are complex questions that are the central part of current debate about reforming the food production business in an effort to hold all food production stakeholders responsible for food contamination. This is a very hard process; for example, recently a frozen berry mix was found to contain a contaminant. In the mix were berries from multiple countries and dozens of farms. How can investigators locate the primary source of the contamination? They can’t! Food safety at home As consumers, it is nearly impossible to know where your food comes from and how it was grown or processed. To prevent a foodborne illness from happening to you there are simple preventative measures to take in your kitchen. Always washing your produce will remove pesticides and herbicides, as well as any heavy metals that are on the produce as dust. Always cooking meat thoroughly will kill microbes living in the raw meat, and keeping separate cutting boards and knives for meat and produce will lower the possibility that the bacteria from raw meat end up in your uncooked food. 6. Organic food is safer to eat: aa. True. bb. False. Figure 6: Keeping separate cutting boards will lower the possibility that the bacteria from raw meat will contaminate uncooked foods. Is organic food better? Wo r k b o o k Lesson 1.3 5. All of the following are challenges the FDA faces in determining the source of a contaminant, except: aa. It is impossible to determine what the contaminant is. bb. Produce from a single farm is shipped all over the world. cc. Produce from multiple farms is used in a single product. dd. The food can be contaminated anywhere in the production process. Choosing to eat organic produce and meats may lower your consumption of specific contaminants, but elevate your risks of others. Organic produce is not grown with synthetic herbicides and pesticides, and are GMO free. Meats that have been raised organic are only fed organic feed, and are raised on land that is free of synthetic fertilizers, pesticides and herbicides. However, they are also more likely to use natural fertilizers like manure that may harbor microbial contaminants. In addition, some people argue that more pesticides and herbicides are used on organic crops, because the types of herbicides and pesticides allowed are not as effective as the synthetic versions. So, in order for those pesticides to be affective, farmers may have to use more of them, leading to more of the chemicals on your food. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 27 LESSON READINGS DEFINITIONS OF TERMS Residue — A small amount of something that remains after the main part has gone. For a complete list of defined terms, see the Glossary. Figure 5: Each year the non-profit organization the Environmental Working Group compiles a list of produce with the highest levels of pesticide residues, called The Dirty Dozen. Wo r k b o o k Lesson 1.3 For consumers that are concerned about consuming chemical herbicides and pesticides, The Dirty Dozen and the Clean Fifteen lists can be used as a guide. These lists are compiled each year from data collected on all major types of produce grown or imported to the United States. The Dirty Dozen are the fruits or vegetables with the highest levels of pesticide residue, and The Clean 15 are the fruits and vegetables with the lowest levels of pesticide residue. The types of produce that end up on The Dirty Dozen list usually are those types that you eat the peel (like apples, grapes and nectarines), or root vegetables that can soak up chemicals underground (like potatoes). Choosing the organic version of the produce on The Dirty Dozen list may reduce your exposure to synthetic pesticides and herbicides, however the only way to ensure that no pesticides and herbicides are on your produce is to grow it yourself on land that has not been contaminated – which is not an easy option! ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 28 STUDENT RESPONSES Imagine that you were put in charge of preventing food contamination in processed foods. What steps would you take? What challenges would you face? _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ ____________________________________________________________________________________________________ Remember to identify your sources _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ Wo r k b o o k Lesson 1.3 _____________________________________________________________________________________________________ ___________________________________________________________________________________________ 29 TERMS TERM DEFINITION Heavy metals A metal with relatively high density or a high relative atomic weight. Lead, mercury and cadmium are all heavy metals. Microbes A microorganism, such as a bacteria or virus, that causes a disease or fermentation. Residue A small amount of something that remains after the main part has gone. For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 1.3 30 LESSON 1.4 WORKBOOK Virtual Calorimetry lab DEFINITIONS OF TERMS Calorimetry — The measurement of quantities of heat. Macronutrient — A substance required in relatively large amounts by living organisms, namely carbohydrates, lipids and protein. We have previously been discussing the characteristics of food, food additives and food safety. In this lesson we will consider the nutritional components of food that were briefly mentioned in Lesson 1.1. In the next two lessons we will learn about the major macronutrients and micronutrients that are in our food, and explore the relationship between macronutrients and calories. We have all heard of a CALORIE, but what is it? Micronutrient — A substance required in relatively small amounts by living organism, like vitamins and minerals. For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 1.4 Figure 1: One Calorie is equal to the amount of energy needed to warm one kilogram (or about one quart) of water by one degree Celsius. Also note that one Calorie, with a capital C, actually means 1,000 calories, or 1 kilocalorie. Even though you may see calorie written sometimes, when it is referring to food you can assume that it really means Calorie. You are probably familiar with the idea that eating food provides us with the energy we need to live. Indeed, the amount of energy in any given food can be found on its label, listed as the number of Calories. But what does this unit of energy mean to us? To address this question let's look at how we measure the Calories in food. Energy can exist in many forms: heat is one form of energy that you can feel, and the bonds that hold molecules together contain energy that can be released as heat when the bonds are broken. As we will see, all the energy we get form food comes from breaking carbon-carbon bonds in macronutrients to release energy. Calorimetry is a laboratory technique that is used to calculate how much energy is in a given substance by burning it and measuring the heat released, and the amount of energy is described in units of Calories. We tend to think of Calories in regards to food, but it can also refer to the other types of energy. In technical terms, calorimetry is the study of the amount of energy that is exchanged between a substance 1. Calorimetry is: aa. A way to measure how much energy is in something. bb. A way to determine the temperature of something. cc. The measure of nutrients in a food. dd. A technique that is no longer in use. 2. Which of the following statements about Calories is true? aa. Some Calories are good, some are bad, depending on the food they come from. bb. If you don't exercise, you aren't using Calories. cc. We get Calories from food through the energy stored in molecular bonds. dd. Cold food has fewer Calories than hot food. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 31 LESSON READINGS and its surroundings before and after a chemical or physical reaction, as measured by changes in heat. When we think about Calories in food we are referring to the energy in the molecular bonds of the macronutrients, as you will see throughout this lesson. History and use of the calorimeter DEFINITIONS OF TERMS Combustion — The process of burning something. For a complete list of defined terms, see the Glossary. In the late 1700s a French scientist named Antoine Lavoisier developed the first known calorimeter, which he used in a series of studies that led him to conclude that animals produce energy through combustion. Lavoisier’s work laid the foundation for future studies in metabolism, leading many people to call him “the father of nutrition”. Since Lavoisier’s early experiments, several types of calorimeters have been developed, all using the same premise of measuring the amount of heat given off by combustion. A combustible reaction is when something with carbon reacts with oxygen (by burning it), yielding carbon dioxide. This reaction is the underlying foundation of metabolism, when the carbon-carbon bonds in glucose are broken/ metabolized to release energy: Figure 2: Antoine Lavoisier, “the Father of Nutrition”, developed an early version of the calorimeter. C6H12O6 (glucose) + O2 (oxygen) → CO2 + H2O + energy (heat) We breathe in the oxygen, which is used to metabolize our food. When glucose is broken down the bonds are broken, and this is where the energy in our food comes from. The CO2 and H2O that is created during metabolism is released from our bodies through sweat and our breath. In fact, we exhale approximately 182 grams of carbon each day, which is about the amount found in 2,200 Calories of food! Wo r k b o o k Lesson 1.4 Calories are a unit of energy that we think of in terms of heat, but how does measuring Calories in a calorimeter relate to the way food is metabolized in our bodies? In the late 1800s a scientist named Wilber O. Atwater developed a respiration calorimeter: a small room just large enough for a person to step into, which measured the changes in oxygen, carbon dioxide and heat. Atwater used the idea that combustible reactions are occurring in our bodies all of time, and that by measuring the oxygen, carbon dioxide and heat coming from a person he could calculate the amount of energy being used by the body. Upon making these measurements after a person in the respiration calorimeter consumed a variety of foods, Atwater determined the number of Calories in carbohydrates, proteins and fats, values that are still used today. 3. Combustible energy is NOT: aa. How we get energy from our food. bb. The type of energy needed to make ice melt. cc. The energy given off when something reacts with oxygen. dd. The energy given off when something is burnt. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 32 LESSON READINGS Explosive science: Bomb Calorimetry DEFINITIONS OF TERMS Basal metabolic rate (BMR) — The rate that the body uses energy while at rest to keep vital functions going, such as breathing and keeping warm. For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 1.4 Figure 3: A bomb calorimeter is used to measure the heat of a reaction. Through lighting food on fire, the amount of Calories in that food can be calculated. As you can imagine, using the complicated respiration calorimeter to measure Calories in all types of foods is not feasible. A common way to measure Calories is the bomb calorimeter. In this technique, the food of interest is weighed and placed in a container that is submerged in water. The food is lit on fire, causing a combustion reaction with the food. The burning food will heat up the surrounding air, which will escape through a copper tube or coil. This air will then heat up the water, and the change in temperature of the water is used to calculate the Calorie content of the food. The food will be weighed again after the reaction so that the Calories per gram of food can be determined. This is how the Calorie information on the back of your food packages is determined. Is counting Calories helpful? Now that we have a better idea of what a Calorie is, how do you know how many Calories to eat? Every person needs a different amount of calories, depending on their activity level, gender, age, weight and height. For example, days that you exercise you may need to eat more food to maintain your energy level compared to days when you are sitting in class for hours at a time. Let's say we have two identical people, but one runs 3 miles, while the other plays video games. The one that runs will need to eat about 300 more Calories to ‘pay’ for the exercise. In addition to the energy you use when you exercise, the number of Calories that you need is the amount of Calories you use to maintain bodily functions; this is called the basal metabolic Figure 4: In 2010 Dr. rate (BMR). Each person will have a Mark Haub made headunique BMR, that will depend largely lines for losing 27 lbs. by upon how much energy is required to eating only processed maintain your body mass. For example foods like Twinkies. The individuals with more muscle mass will trick? He cut his Caloric intake in half, adding evihave a higher BMR than people that dence to the belief that it have more fat mass. In general, the isn’t the nutritional value more muscle a person has, the higher of food that you eat their BMR will be. Knowing how many that leads to weight gain Calories you need to maintain a healthy or weight loss, it’s the weight will help you decide what foods amount of total Calories. are better choices for you. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 33 LESSON READINGS Are all calories created equal? DEFINITIONS OF TERMS Caloric density — The number of Calories relative to a volume of food. Empty calories — The energy available in high-energy foods that have little to no nutritional value. For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 1.4 Let’s say you perform bomb calorimetry on a candy bar and an apple and peanut butter and find that the number of Calories in each is identical. Are the Calories equal? Foods that have a lot of added sugars and unrefined carbohydrates are sometimes said to have 'empty calories'. For example, the candy bar is full of empty calories, but the apple with peanut butter has Calories plus other nutritional value, like vitamins, minerals and fiber. So, what the term empty calorie hints at is the amount of micronutrients per Calorie in the food; a food with a lot of Calories, but without the beneficial vitamins and minerals has a lot of empty Calories. In this way, the Calories from the fruit seem to be ‘better’ than the Calories from the candy bar. But be careful, the term 'empty calories' is a bit of a misnomer, because the food is not empty of calories, but is instead empty of beneficial nutrients. People that eat a diet full of empty Calories, like Dr. Haub in the photo above, must rely on a nutrition supplement to supply them with their other nutritional needs. So, all calories are equal but two foods supplying the same number of calories may be unequal. The USDA has recommended daily intakes for empty calories based on gender, age and physical activity to ensure that we all eat enough of the important micronutrients without overeating Calories. For example, if you are supposed to eat 2000 Calories in a day, and you eat 300 empty Calories then you need to get all your micronutrients in the reaming 1700 Calories that day. For a teenaged male exercising 30 minutes a day, it is recommended that he consume no more than 265 empty calories a day. A female of the same age and physical activity level should consume no more than 160 empty calories a day. This is about the amount of Calories in one candy bar or soda. Caloric density In terms of choosing food to maintain a healthy weight, or for weight loss or weight gain, it is the number of Calories eaten that will make the most difference. Caloric density is defined as the amount of energy provided per a measured volume of food. It can also be thought of as the absence of components in food that do not give you energy: water and non-digestible substances like fiber. For example, something that is high in fat will be more calorically dense than something high in protein or carbohydrates, because lipids have more calories per gram (9 Calories per gram) than protein (4 Calories per gram) or carbohydrates (4 Calories per gram). Figure 5: High fiber foods like vegetables will fill your stomach for little calories, unlike calorically dense fats like oil, or fiber free proteins like chicken. 4. Caloric density: aa. Describes the nutritional value of a food. bb. Is higher in foods with a lot of fiber. cc. Would be high in a diet soda. dd. Can tell you how much energy is in a food relative to other foods. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 34 LESSON READINGS A tablespoon of oil will have more calories than a tablespoon of sugar, so the oil is more calorically dense than sugar. Additionally, processed foods are likely to be more calorically dense than whole foods, because the act of processing food breaks down and removes fiber. We can also think of caloric density in the reverse: what volume of a food do you need before you reach a certain number of Calories? In Figure 5 you can see that 400 Calories of oil does not take up as much volume as 400 Calories of chicken or vegetables. Serving sizes and the calorie surprise! The more often you pay attention to the number of Calories in foods, the more likely you are to be surprised by where Calories can hide. Using the pictures below, take a moment to rank the foods from the lowest to highest number of Calories: Small french fries Ham and cheese sandwich 16 oz. flavored coffee drink Wo r k b o o k Lesson 1.4 Beef, bean and rice burrito Single serving of Ranch salad dressing Bottle of soda ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 35 LESSON READINGS DEFINITIONS OF TERMS Which food do you think contains the most Calories? In the pictures on the previous page, the salad dressing has the fewest Calories, with only 150. A serving of salad dressing however is only 2 tablespoons, about the size of a golf ball, and we tend to pour on more than one serving. A small serving of french fries at a popular fast food restaurant will add around 250 Calories to your meal. Beverages are a top source of unexpected Calories because they don’t have any fiber and are usually laden with sugars to make them sweeter. For example, a 16 oz. bottle of soda contains around 190 Calories, and a medium flavored espresso drink with whole milk from a popular coffee shop can contain 400 – 500 Calories! A ham and cheese sandwich with lettuce and tomato on wheat bread only contains around 350 Calories. A burrito from a fast food chain with steak, rice, beans and cheese has nearly 1000 Calories! Did any of these surprise you? The absorption dilemma! Digestible energy — The energy that is available by digestion. This can be measured as the difference between the amount of energy eaten and the amount of energy excreted in the feces. Microbiome — The community of microorganisms that live in or on our bodies. As previously mentioned, the Calories that are listed on a Nutrition Facts panel of foods were measured using a bomb calorimeter. However, two foods containing the same number of Calories may be digested and absorbed differently in our bodies. For example, if you measure the number of Calories in raw vegetables and cooked vegetables, the calorimeter will tell you that the number of Calories has not changes significantly. Your body, on the other hand, cannot absorb all of the proteins and carbohydrates in uncooked vegetables because they are still tangled up in the fibers of the vegetable. This brings up the idea of digestible energy, which is the amount of energy from food that you actually absorb. So the number of Calories listed on foods tells us the maximum amount of energy we could absorb from the food, unfortunately there is no easy way to measure digestible energy. In general, energy is readily absorbable from foods composed of empty calories, while whole foods that are likely to have less digestible energy than total Calories. For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 1.4 Figure 6: Enterococcus faecalis is a kind of commensal bacteria that lives in the gut. The amount of digestible energy that is absorbed may also vary from person to person, and can depend on your health, age, ethnicity, and microbiome. Your microbiome is the world of microorganisms, mostly bacteria, which have adapted to living in your intestines. These bacteria feed off of the indigestible part of your diet, like fiber. They will help to break down these fibers into smaller particles that you can more readily absorb, similar to the way cooking can release nutrients. The types of bacteria that live in your gut are unique to you, much like a fingerprint. Some research suggests that people who are obese have a very different microbiome compared to people that are thin. This might mean that the microbiome of an obese individual is better at breaking down foods, so that person can absorb more digestible energy. 5. The digestible energy in a food depends upon all of the following except: aa. Your microbiome. bb. The fiber in the food. cc. Your exercise level. dd. Your age. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 36 STUDENT RESPONSES If you drank 150 Calories from a soda, or ate 150 Calories in a sandwich, which one will you absorb more energy from? Why? _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ ____________________________________________________________________________________________________ _____________________________________________________________________________________________________ Remember to identify your sources _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ Wo r k b o o k Lesson 1.4 _____________________________________________________________________________________________________ ___________________________________________________________________________________________ 37 TERMS TERM For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 1.4 DEFINITION Basal Metabolic Rate The rate that the body uses energy while at rest to keep vital functions going, such as breathing and keeping warm. Caloric Density The number of Calories relative to a volume of food. Calorimetry The measurement of quantities of heat. Combustion The process of burning something. Digestible Energy The energy that is available by digestion. This can be measured as the difference between the amount of energy eaten and the amount of energy excreted in the feces. Macronutrients A substance required in relatively large amounts by living organisms, namely carbohydrates, lipids and protein. Microbiome The community of microorganisms that live in or on our bodies. Micronutrients A substance required in relatively small amounts by living organism, like vitamins and minerals. 38 LESSON 1.5-6 WORKBOOK Macro- and Micronutrients; Review of nutrients and virtual calorimetry lab DEFINITIONS OF TERMS Monomer — Mono means ‘one’, Mer means ‘part’. A molecule that can be bonded to identical molecules to form a polymer. Polymer — Poly means ‘many’, Mer means ‘part’. A substance consisting chiefly or entirely of a large number of similar units bonded together. For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 1.5-6 You now know what a Calorie is and how it relates to the energy we absorb from food. In this lesson we will continue discussing the characteristics of macro- and micronutrients that are found in foods. We will learn about the structural patterns of the three macronutrients, and highlight certain food sources rich in these nutrients. Macronutrients Have you ever heard someone proclaim ‘you are what you eat’? Stop and think about that phrase – how can it be true? It turns out that in addition to giving us energy, food plays an important role in providing the building blocks our cells and tissues need to grow and sustain life. Nutrients that you need to eat in large quantities are called macronutrients. Carbohydrates, lipids and proteins are the three types of macronutrients, and are used by your body for both energy and as building blocks for the body’s structures. After you have eaten enough food to meet your energy needs, your body will start to use these macronutrients to build new cells and cellular components. Carbohydrates, lipids and proteins can all be found in foods in various forms, ranging from small easy to digest fragments to large bulky molecules. We can think of the smaller versions of each macronutrient as the monomer form, and the larger version as the polymer form. The monomer form of each micronutrient is the version from which we derive energy, whereas we are more likely to eat the polymer version in foods. As we will see, our bodies can convert between the monomer and polymer versions of all three macronutrients to derive energy and to build structures. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 39 LESSON READINGS Carbohydrates Food sources and recommended intake DEFINITIONS OF TERMS Disaccharide — Any of the sugars that contain two monosaccharides linked together. Fiber — An indigestible dietary substance consisting of a large number of sugar monomers joined together by beta bonds. Monosaccharide — Any of the sugars that cannot be hydrolyzed to give a simpler sugar. Starch — A carbohydrate consisting of a large number of glucose monomers joined together by alpha bonds. Produced in most green plants as energy storage. Sugar — A class of water soluble, crystalline, typically sweet-tasting carbohydrates. For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 1.5-6 Carbohydrates are sugars, starches or fibers and are found in breads, cereals, pasta, rice, fruits, starchy vegetables like potatoes, corn, dairy products and anything with added sugar. They are the primary energy source for our cells, yielding about 4 calories of energy per gram of carbohydrate. Plants provide Figure 1: Adults need about 130 g the main source of carbohydrates – during photoper day of carbohydrates for glucose to feed the body and the brain. synthesis they produce glucose from carbon dioxide, water and energy from the sun. They either store the glucose, or transform it into starch, fiber, fat or protein. The USDA recommends that calories from carbohydrates should constitute about 45% - 65% of our daily energy intake, so they are a major part of our diet. Adults need about 130 g/day of digestible carbohydrates to supply adequate glucose for the brain and central nervous system. In general, people in the United States eat plenty of carbohydrates, with wheat flour, soft drinks and potatoes being top contributors of carbohydrates in our diet. Simple sugars – the carbohydrate monomers The structures of carbohydrates relate to their functions in the body. Like all of the macronutrients, carbohydrates have smaller building blocks (monomers) that are assembled into more complex, larger structures (polymers). Our bodies easily absorb the simple, smaller structures, but must break down the complex structures before absorption. The small versions of carbohydrates are simple sugars, which come as either monosaccharides or disaccharides. These carbohydrates taste sweet, and are found naturally in fruits and milk, or as added sugars in other foods. The monosaccharides are glucose, fructose and galactose. ■■ Glucose is the main macronutrient used by our cells for energy. Its levels in the blood are tightly regulated and dysregulation causes diabetes. ■■ Fructose is the monosaccharide that is in fruits, sweet vegetables like carrots or sweet potatoes, honey and corn syrup (although honey and corn syrup both contain glucose as well). ■■ Galactose is mostly found in dairy products in combination with glucose, which makes lactose, a disaccharide. 1. What is the simplest form of carbohydrate? aa. Starch. bb. Glucose. cc. Sucrose. dd. Fiber. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 40 LESSON READINGS DEFINITIONS OF TERMS Alpha bond — A chemical bond linking monosaccharides to form disaccharides or a complex carbohydrate that is easily digested. Amylopectin — A type of starch consisting of branched sugar chains. Amylose — A type of starch consisting of long unbranched sugar chains. Beta bond — A chemical bond linking monosaccharides to form disaccharides or a complex carbohydrate that is not easily digested. Glycogen — A substance in the liver and some muscles that is a store of carbohydrates. Consists of highly branched sugar chains. Monosaccharides are generally drawn as a hexagon, like those in Figure 2, because this is the shape the carbon atoms in the molecule form. Each corner in the hexagon represents one carbon. In the body, glucose is known as ‘blood sugar’, because it is the form of sugar that is transferred by the blood to tissues. Although it is the most abundant type of carbohydrate in our bodies, we eat very little glucose as a monosaccharide. This is because plants generally store glucose in more complex forms, so most glucose in our diet is found as a disaccharide or complex carbohydrate. Monosaccharide Disaccharide Complex saccharide Figure 2: Saccharides, meaning sugars, are found either alone (mono), in pairs (di), or in a string (complex). Disaccharides contain two simple monosaccharides bound together. There are two types of bonds that can occur between monosaccharides: an alpha bond or a beta bond. Enzymes in our intestine break these bonds to convert the disaccharide into monosaccharides before being absorbed. In general, alpha bonds are easier to digest than beta bonds. The most common disaccharide is sucrose, or table sugar, and is composed of glucose and fructose by an alpha bond, making it very easy to digest. Lactose, the disaccharide made of galactose and glucose, contains a beta bond and requires a specialized enzyme to digest it. Some people do not make this enzyme and cannot digest lactose, leading to lactose intolerance. Amylose( For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 1.5-6 Amylopec+n( Glycogen( Figure 3: Amylose is a simple chain of monosaccharides, whereas amylopectin and glycogen have many branches. This allows for digestive enzymes to quickly break sugars off of each end. 2. Disaccharides are: aa. Three monosaccharides. bb. One monosaccharide. cc. Two monosaccharides. dd. None of the above. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 41 LESSON READINGS Complex carbohydrates – the carbohydrate polymers DEFINITIONS OF TERMS Cellulose — An insoluble complex carbohydrate that is the main constituent of plant cell walls. Consists of long chains of glucose monomers. Insoluble fiber — Dietary fiber that is not water-soluble. This fiber adds bulk to the diet, preventing constipation. Pectin — A soluble gelatinous complex carbohydrate that is present in ripe fruits and is extracted for use in jams and jellies. Soluble fiber — Dietary fiber that is water-soluble. This fiber type can absorb water and bile in the intestine to form a gel, making you feel full. For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 1.5-6 Complex carbohydrates also come in two forms: starch, which is digestible, and fiber, which is indigestible. As shown in the figure above, starches are chains of monosaccharides. Digestible starch contains hundreds of thousands of glucose molecules linked by alpha bonds. Making this long chains of glucose provides a way to store glucose for later use. Plants store glucose as amylose (also known as starch) and amylopectin, whereas animals store glucose as glycogen. Digestive enzymes can release glucose from these storage forms by breaking off the glucose molecules on the ends of the chains. As you can see in Figure 3, both amylopectin and glycogen are highly branched molecules, which means that they have lots of sites where the digestive enzymes can break them down to individual monosaccharides, allowing both amylopectin and glycogen to provide glucose very quickly. Fiber is an indigestible component to our diet that can be either Pectin: Soluble Fiber soluble or insoluble. We get fiber Bran layers in our diet from different parts of (Hemicellulose plants. For example, the juicy inside and lignan): Insoluble Fiber of an apple, or the endosperm of a wheat kernel contain soluble fiber. The fibrous part of a plant, like the Cellulose in skin of an apple or the bran of a the skin: Insoluble wheat kernel, contains insoluble Fiber fiber. Pectin is a soluble fiber used to make foods gelatinous. Because Figure 4: Cellulose is the insoluble fiber found mostly soluble fiber can absorb water, as the skin or the ‘tough’ parts of produce. Insoluble it expands in your intestines and fiber, like pectin, can be found in the softer or chewier makes you feel full. Cellulose is an parts of produce. insoluble fiber found in all plant cell walls made up of glucose monosaccharides connected by beta bonds, making it impossible for the intestinal enzymes to break it down. Because fiber is indigestible in the small intestine, it passes through to the large intestine where it is broken down by bacteria in our microbiome. Although we do not absorb fiber it plays a role in our health. Complex carbohydrates are absorbed slower than simple sugars It is common for dieters to remove carbohydrates from their diet in an attempt to lose weight. Carbohydrates have received a bad reputation, being blamed for everything from sugar addictions to food allergies. It is important to realize that ‘carbohydrates’ is an umbrella term that refers to a wide variety of nutrients, and each type of carbohydrate behaves differently in our bodies. For example, our bodies easily take up 3. Complex chains of glucose in animals are stored as: aa. Amylose. bb. Amylopectin. cc. Glycogen. dd. Fiber. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 42 LESSON READINGS simple sugars, so they get into our blood stream quicker than complex carbohydrates like starches that need to be digested before being absorbed. We will learn more about this in Unit 2 when we study digestion and absorption of foods. Lipids Food sources and the recommended intake DEFINITIONS OF TERMS Cholesterol — A molecule that contains loops or rings of carbons. Used in cell membranes and to make hormones. Fatty acids — A molecule that is naturally in fats and oils with a long chain of carbons. Triglyceride — A molecule formed from glycerol and three fatty acids. Triglycerides are the main type of fat found in natural fats and oils, and is the form that fat is stored as in the body. For a complete list of defined terms, see the Glossary. Lipids may be oils or fats, and are found to some degree in nearly every food that we eat. The foods richest in fats are vegetable oils, margarine, butter, avocado and nuts, which contain close to 100% of their energy as fat. Many protein-rich foods, such as meat, cheese and peanut butter are also high in fat. Figure 5: Adults are recommended As we saw in the calorimetry lab, fats are a compact to get 20-35% of energy intake from source of calories – gram for gram they supply more fats. than twice as many calories per gram compared to carbohydrates and proteins – 9 calories/gram. Fats are the main source of energy storage within our bodies and are an essential nutrient. Besides storing energy, fat insulates and protects the body by surrounding internal organs and providing added cushioning and protection. This is one reason that people with less body fat often feel cold. There is no recommended intake of fat from the USDA, but other organizations recommend that 20-35% of energy intake comes from fats in the diet. Molecular structure and functions of the lipids Lipids are composed of carbon hydrogen and oxygen. They do not dissolve in water, and this property is important for how they function in the body. Like carbohydrates, fats can be packaged into small and larger forms, including fatty acids, triglycerides and cholesterol. ■■ Fatty acids are long chains of carbons used as building blocks for other fats or as an energy source. ■■ Triglycerides are made up of three fatty acids linked by another molecule called glycerol. They are how most fatty acids are transported throughout the body and stored. Wo r k b o o k Lesson 1.5-6 ■■ Cholesterol can be either synthesized by the liver or consumed from animal products. Like triglycerides, cholesterol is composed of fat acids packaged with other molecules. Cholesterol is a building block for hormones and other structures in the body including cell walls. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 43 LESSON READINGS Fatty acids – The lipid monomers DEFINITIONS OF TERMS Cis — A shape of chemical bond where two types of structures lie on the same side of the bond. Will make the bond have the shape of a ‘C’, creating a bend in the molecule. Saturated bond — A type of chemical bond that has the maximum number of hydrogens. Trans — A shape of chemical bond where two types of structures lie on opposite sides of the bond. Will make the bond have the shape of a ‘Z’, creating a straight molecule. Fatty acids are the simplest form Saturated fatty acids are always solid of lipids, even though they are still rather long chains of carbons. Fatty acids can be broken down, releasing the combustible energy in the Unsaturated fatty acids can be solid or liquid molecular bonds for our cells to use. Similar to the alpha beta bonds in carbohydrates, the linkages between carbons in fatty acids impact their Figure 6: Saturated fatty acids are a straight line of carfunction. There are two different bons, allowing them to stack and be solid at room temkinds of linkages in a fatty acid chain perature. Unsaturated fatty acids have a kink that allows – saturated or unsaturated. Saturatthem to move around and be liquid at room temperature. ed means that all the carbon bonds are filled up with hydrogen (single bonds), and unsaturated means that some of the carbon molecules are missing a hydrogen (double bonds). The double bond creates a kink in the fatty acid, making it more difficult to stack them on top of each other. You can see how the shapes of saturated and unsaturated fatty acids compare in Figure 6. Think about the how easily toothpicks can neatly stack on top of one another. Now if you were to slightly break the toothpicks so that they were all bent, could you make the same, neat pile? The bent toothpicks are like the unsaturated fatty acids, and it is this kink in their structure that makes them liquid at room temperature, whereas the perfectly straight saturated fatty acids are solid. Animal fats, like butter, are saturated fatty acids, and most plant sources of fats, like vegetable oils, are unsaturated fatty acids. Unsaturated bond — A type of chemical bond in which one or more hydrogens is missing. The infamous ‘trans’ fat For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 1.5-6 Figure 7: Trans fats have long shelf lives but rise our ‘bad’ cholesterol. While most natural forms of unsaturated fatty acids are kinked, thus liquid, there is a type of unsaturated fatty acid that is solid. This is because the carbons forming the kink in the unsaturated fatty acids can be linked by two shapes of bonds. They can be bent (called cis) or straight (called trans). The cis fatty acids are found in nature as vegetable and fish oils, and are liquid at room temperature as we discussed above. Most the trans fatty acids in our diets come from processed foods. Food manufacturers will synthesize trans fatty acids because they are stable and have a long shelf life. Unfortunately, eating trans fatty acids is bad for our health, and can lead to increased ‘bad’ cholesterol and decreased ‘good’ cholesterol. 4. Triglycerides are: aa. Long chains of fatty acids. bb. Short chains of fatty acids. cc. Chains of fatty acids linked by double bonds. dd. Chains of fatty acids linked by glycerol. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 44 LESSON READINGS Essential fatty acids Humans are able to make a wide variety of fatty acids themselves, however there are two that they cannot make and which must be eaten as nutrients, called essential fatty acids. They are used to keep the cell wall supple and flexible so substances can flow in and out. They are also used to produce, hormones with over 100 different actions, such as regulating blood pressure, blood clotting, sleep, inflammation, and asthma reactions. The two essential fatty acids are: Glycerol — A water-soluble component of triglycerides that connects the three fatty acids together. Omega-3 fatty acid — An unsaturated fatty acid that occurs mainly in fish oils. Contains three unsaturated bonds. Omega-6 fatty acid — An unsaturated fatty acid that occurs mainly in vegetable oils. Contains two unsaturated bonds. For a complete list of defined terms, see the Glossary. ■■ Omega – 6 fatty acid is found in beef, poultry, safflower oil, sunflower oil and corn oil. Note that both of the essential fatty acids are found in animal and plant sources, but the fatty acids in the plants require extra steps once they’re absorbed to make them useful to us, so they do not provide the same level of benefit as the essential fatty acids from meat and fish. Triglycerides – the polymers of the lipids For storage in cells and transport through the blood fatty acids are linked in groups of three with a glycerol molecule. This form of fatty acids is called a triglyceride. Glycerol" Essential fatty acids — Fatty acids that humans cannot make on their own, so must be eaten in the diet. ■■ Omega – 3 fatty acid is found in cold-water fish like salmon, tuna, sardines and mackerel. It is also found in walnuts, flaxseed, hemp oil, canola oil and soybean oil. Fa#y%Acid%1% Fa#y%Acid%2% short" Medium chain fatty acids come from coconut and palm oil Fa#y%Acid%1% Fa#y%Acid%2% Fa#y%Acid%3% Wo r k b o o k Lesson 1.5-6 Short chain fatty acids come from butter and whole milk Fa#y%Acid%3% Glycerol" DEFINITIONS OF TERMS Long chain fatty acids come from meat and plant oils long" How long to digest Figure 8: Triglycerides are made up of a glycerol backbone and three fatty acids. The length of fatty acid chains on triglycerides will determine how long it takes to digest them. Triglycerides are the major form of fat found in foods. As Figure 8 shows, each triglyceride molecule consists of three fatty acids attached to a glycerol backbone. All fatty acids have similar structures, and the carbon chains usually have between 4 and 24 carbons. 5. Saturated fatty acids: aa. Are usually liquid at room temperature. bb. Are usually solid at room temperature. cc. Contain double bonds. dd. Both B & C. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 45 LESSON READINGS ■■ Long chain fatty acids (>24 carbons) come from meat and most plant oils. They take the longest to digest. ■■ Medium chain fatty acids (6-10 carbons) are found in coconut and palm oil; they are digested almost as fast as glucose. ■■ Short chain fatty acids (<6 carbons) are found in butter and whole milk. Triglycerides are the body’s main form of energy storage. Excess calories from carbohydrates, fats, proteins and alcohol can be converted to fatty acids and then assembled into triglycerides. They make an excellent Figure 9: Longer fatty acids take longer to digest. ‘savings account’ of energy because they are stable and calorie dense. Triglycerides are mostly stored in fat cells, and a single fat cell can increase in weight about 50 times when full of fat. When they max out, new fat cells can form. As we will see in later units, very large stores of fat can pose numerous health risks. Cholesterol has a different structure than fatty acids and triglycerides Wo r k b o o k Lesson 1.5-6 The structure of cholesterol is like looped, or circularized fatty acids; instead of straight chains of carbons, the carbons are arranged in rings. Our body can make cholesterol from glucose, amino acids and fatty acids, so we don’t need a lot of it in our diet. In fact, our liver tightly regulates how much cholesterol is made, so if you eat a lot of cholesterol in your diet, your liver will make less. In the diet, cholesterol can be found in meats and animal products like milk, butter and cheese. Instead of being a way to store energy, like fatty acids and triglycerides, cholesterol has other central functions in the Figure 9: LDL is a larger molecule that carries body. Cholesterol is used to make hormones lipids through the blood, depositing them in like testosterone, estrogen and vitamin D, tissues. HDL is smaller and removes extra lipids from the blood, bringing them back to the liver and is important in the transportation of for processing. triglycerides and fatty acids in the intestines and blood. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 46 LESSON READINGS Cholesterol helps transport lipids If you’ve ever tried to mix oil and vinegar to make salad dressing, you already know that fats are not soluble in water. Two terms are used to describe whether a molecule is soluble or insoluble in water. Things that like water are called hydrophilic, and things that don’t like water are hydrophobic. Fats are hydrophobic, but carbohydrates and proteins are hydrophilic. DEFINITIONS OF TERMS HDL (High-density lipoprotein) — A type of lipoprotein that transports lipids in the blood from tissues and arteries to the liver for processing. Hydrophilic — Hydro means ‘water’, Philic means ‘loving’. Having a tendency to mix with or dissolve in water. Hydrophobic — Hydro means ‘water’, Phobic means ‘fearing’. Tending to repel or fail to mix with water. LDL (Low-density lipoprotein) — A type of lipoprotein that transports lipids in the blood from the liver to tissues and arteries. Legumes — A family of plants with seeds that grow in long cases. Beans, peas and peanuts are legumes. Lipoprotein — A group of watersoluble proteins that combine with and transport lipids in the blood. For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 1.5-6 Our bodies have a lot of water in them, so in order for fats to be absorbed and transported in the blood they have to be packaged up so that the hydrophobic fats are on the inside of a hydrophilic capsule. To do this, lipids are transported in the blood in a capsule called a lipoprotein. From the name you can tell that this molecule has both lipids and proteins. When you eat something high in fat, the liver will repackage those fatty acids, triglycerides, and cholesterol into lipoproteins. High-density lipoprotein (HDL) is often referred to as ‘good’ cholesterol because it is responsible for removing extra fat from the cardiovascular system and other tissues. HDL gets its name because it has more protein than fat, making it denser. Low-density lipoprotein (LDL) on the other hand is the ‘bad’ cholesterol. Opposite to HDL, LDL’s role is to bring fat to tissues and the cardiovascular system. It has more fat relative to protein, making it a lower density molecule compared to HDL. Even though HDL and LDL are often referred to as cholesterol themselves, cholesterol is only a part of their structure, as they are actually a lipoprotein. Figure 10: Eating foods rich in unsatured fatty acids may increase HDL levels. Proteins Food sources and the recommended intake Proteins are found in both meats and vegetables, although they are more concentrated in animal sources. Although they are often used in the body for structural purposes they can yield 4 calories/gram of protein. In the typical North American diet, meat, poultry, fish, milk, cheese, legumes and nuts supply about 70% of our dietary protein with a majority of the protein being provided by animal sources. Worldwide only 35% of protein intake comes from animal sources. Americans typically consume 1.5 - 2 times more protein than they need. It is recommended that healthy people who are not growing or recovering from illness eat between 46-56 grams of protein a day. For healthy adolescents between 13-18 years of age, the recommended intake is 48-52 grams of protein a day to ensure their protein needs are met to build structures as they grow. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 47 LESSON READINGS Amino acids – the protein monomers DEFINITIONS OF TERMS Amino Acid — A monomer used to build proteins. Contains a nitrogen-containing amino end, and an acid end. Amino group — A chemical group that contains nitrogen and hydrogen. This group is basic, or alkaline. Carboxyl group — A chemical group that contains carbon, oxygen and hydrogen. This group is acidic. Peptide — A compound consisting of two or more amino acids linked in a chain. These chains of amino acids are shorter than polypeptides. R chain — A generic name for a side chain on a molecule. For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 1.5-6 Like carbohydrates and fats, proteins are built by combining a group of monomers into a polymer. Proteins are chains of amino acids, which when linked together are called peptides. As shown in Figure 7, amino acids are composed of a central carbon molecule bonded to four The body uses 20 different kinds different groups: a nitrogen (amino) of amino acid! group; an acid (carboxyl) group; ! hydrogen; and a side chain (often called an R chain). The side chain is made of carbons and makes each amino acid unique. Similar to carbohydrates and lipids, the combustible energy in the molecular bonds in the carbon side chain is where calories are derived from in amino acids. Each%amino%acid%has%a%different%‘R’%group% Figure 11: Each amino acid contains and amino group, a carboxyl (acid) group, a hydrogen and an R-group (side chain). There are 20 different amino acids used by our bodies. Some of these we make, but some must be obtained from our diet. ■■ Essential amino acids: The body must obtain 9 amino acids from the diet either because the body can’t make the carbon skeleton of the R group or it can’t make the amino acid fast enough to meet the body’s needs. Animal products are complete proteins, while plant proteins are usually lacking in one or more essential amino acid, with quinoa and soy being the exception. For this reason, vegetarians and vegans must eat a variety of produce, whole grains and legumes to ensure that they are eating all the essential amino acids. ■■ Non-essential amino acids: The body can make the remaining 11 amino acids itself. Hint: You can remember which amino acids are the essential ones by using the mnemonic PriVaTe TiM HILL: Phenylalanine, Valine, Tryptophan, Threonine, Methionine, Isoleucine, Leucine and Lysine. 6. What are the simplest building blocks of a protein? aa. Amino acids. bb. Glucose. cc. Polypeptides. dd. Peptides. ee. A & D. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 48 LESSON READINGS Polypeptides – the protein polymers DEFINITIONS OF TERMS Connective tissue — A tissue that connects, supports, binds or separates other tissues or organs. Polypeptide — A polymer of a large number of amino acids bonded together in a chain. Forms a protein. Primary structure — The characteristic sequence of amino acids forming a protein or polypeptide chain. Quaternary structure — The structure formed by the interaction of two or more proteins or polypeptide chains. Secondary structure — The local three-dimensional structure of different portions of a protein or polypeptide chain. Tertiary structure — The overall three-dimensional structure of a protein or polypeptide chain. For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 1.5-6 Amino acids bound together The Four Levels of Protein Structure to form chains of polymers are called peptides, or sometimes polypeptides. Like the name implies, polypeptides are polymers of peptides. The sequence of amino acids is called the protein’s primary structure. Remember that DNA codes for RNA, which codes for protein. This code is the sequence or combination of A. Primary Primary Secondary Ter:ary Quaternary the amino acids that determines how the protein folds up. The Figure 12: Which amino acids make up the primary structure of a protein can determine the secondary and tertiary way something bends and folds structure as well. Multiple polypeptide chains will interact to is called the secondary strucform the quaternary structure. ture. Most proteins will then fold more to form a tertiary structure and sometimes different polypeptides will join together to form a complex or quaternary structure. It is this folded polypeptide structure that gives proteins their unique functions. Functions of proteins and amino acids Proteins in our cells or from our diet can be broken into monomer amino acids for the body to use to build new polypeptides. Proteins are a large component of our bodies, making up nearly 20% of our body weight, and are found in muscle, connective tissue, organs, our blood cells, antibodies, hormones and enzymes. So again, you are what you eat! Micronutrients The main way that micronutrients differ from macronutrients is that we do not get any calories from them directly. Instead, our bodies use this class of nutrients to maintain vital reactions that are constantly occurring in our cells. In fact, without some of the micronutrients we could not breakdown macronutrients for energy. As you would guess from the name, micronutrients are usually smaller than macronutrients and are found in much lower quantities in our food. Much of our understanding of the micronutrients’ functions has come from observations made when the micronutrient is taken out of the diet. Therefore, we tend to 7. Multiple amino acids together can form: aa. A polypeptide. bb. A protein. cc. The primary sequence. dd. All of the above. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 49 LESSON READINGS know more about micronutrient deficiencies than we do about their toxicities. For example, if a micronutrient is lacking in your diet your body will not function well. On the other hand, if you have enough of each micronutrient, eating excess probably won’t help you and may even cause harm. You can think of this like the air in your bike tires: if you don’t have enough air your bike won’t work properly, but if you have too much air your tires may pop! DEFINITIONS OF TERMS There are two major types of micronutrients, vitamins and minerals, but a new class of micronutrients called phytonutrients is emerging. All three of these types of micronutrients are discussed below. Vitamins Fat-soluble — A substance that dissolves in fats, not water. Phytonutrients — A substance that is found in certain plants which is believed to be beneficial to human health and prevent various diseases. Water-soluble — A substance that dissolves in water, not fats. For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 1.5-6 Long before vitamins were identified, certain foods were known to cure conditions brought on by what we now know are vitamin deficiencies. For example, during the 15th and 16th centuries, many British sailors on long Figure 13: Scurvy was a disease sea voyages died from scurvy. Scurvy has symptoms common among sailors for centuries like fatigue, inability to think clearly, spots on the skin, until its cause was identified as vitaand bleeding from mucous membranes. In its advance min C deficiency. stages, people may lose teeth, have un-healing wounds, and experience liver and brain failure. After it was discovered that eating lemons and limes prevented scurvy, citrus was included as a routine part of the sailors’ rations and deaths from scurvy sharply declined. We now understand that scurvy results from a deficiency of vitamin C. Our total vitamin needs to prevent deficiency are quite small – about 25 Vitamin B Group grams for every 70 kilograms of food consumed. Water soluble But does eating excess vitamin C have a positive Vitamin c Vitamins or negative effect on the body?Some vitamin deficiencies are still a public health concern Fat Vitamin A soluble today, for example, in many developing counVitamin D tries vitamin A deficiency is a primary cause of childhood blindness, while vitamin D deficiency Vitamin E plays a role in bone disorders. During the first Vitamin K half of the 20th century scientists discovered the 13 vitamins now recognized as essential. For the most part they were named alphabetically in the order they were discovered. Now we categorize Figure 14: Vitamins are classified as either them as fat-soluble or water-soluble. water-soluble or fat-soluble. 8. Micronutrients are: aa. Used for energy. bb. Needed in large quantities. cc. Required for some enzymes to function. dd. What make up macronutrients. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 50 LESSON READINGS Water-soluble vitamins Only small amounts of water-soluble vitamins are stored in the body and they are readily removed by the kidneys and excreted in the urine, which relates to the low risk of water-soluble vitamin toxicity. Compared with fat-soluble vitamins, water-soluble vitamins are more easily destroyed during cooking, and more susceptible to heat, light, air and alkaline substances. Retention is greatest in foods that are prepared by steaming, stir-frying and microwaving, which limit exposure to heat and water. The B vitamin group and vitamin C make up the water-soluble vitamins. DEFINITIONS OF TERMS Alkaline — Having a pH greater than 7, demonstrating that it is basic in nature. Anemia — A condition marked by deficiency of red blood cells or hemoglobin in the blood, resulting in fatigue, pale skin and weakness. Dementia — A chronic mental disorder marked by poor memory, personality changes and impaired reasoning. Vitamin B Group: Functions and food sources Originally all of the vitamins in the vitamin B group were thought to be one vitamin, but we now know there are eight distinct vitamins of this group. The vitamin B group of water-soluble vitamins exemplifies how vitamins work with proteins to increase their efficiency. For example, these vitamins are required for basic cellular functions and deficiency will cause serious problems like anemia and dementia. The vitamin B group can be obtained from meat, grains and legumes. Grains have vitamin B in their husks, but you might recall that this part is removed during the processing of wheat into flour. So, wheat flour is fortified with extra B vitamins before it is sold. The eight B vitamins and their sources and symptoms of deficiency are as follows: Figure 15: Grains, especially fortified wheat flour, are a good source of many B vitamins. ■■ Thiamin: Found in pork products, sunflower seeds and legumes. Deficiency causes beriberi, which means “I can’t, I can’t”. It was given this name because of its symptoms of weakness, pain, difficulty breathing, anorexia, poor memory and confusion. ■■ Riboflavin: Found in milk products, eggs and enriched cereal. Deficiency causes inflammation of the throat, mouth and tongue and cracking of the tissues around the corners of the mouth. For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 1.5-6 ■■ Niacin: Found in poultry, meat, fish and corn. Deficiency causes pellagra, a rough red rash that appears on skin exposed to sunlight, and dementia. The only dietary deficiency disease to reach epidemic proportions in the US – it occurred when corn became a staple in the diet of the poor. In Latin America corn is treated with an alkaline substance that releases the niacin. But when it was first used in the US it wasn’t treated, and niacin deficiency resulted. ■■ Pantothenic acid: Ample in the diet, found in meat, milk and many vegetables including mushrooms. Deficiency has not been observed. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 51 LESSON READINGS ■■ Biotin: Found in whole grains, eggs, nuts and legumes and enriched cereal. Deficiencies are rare except for a genetic disease that slows down biotin breakdown in the intestines. ■■ Vitamin B-6: Stored in the muscles of animals therefore meat, fish and poultry are a good source. The leading sources in the US are fortified cereals, poultry, beef, potatoes and bananas. It can be lost when the foods are exposed to heat and other processing. Deficiency is rare in North America. When it does occur it causes dermatitis and anemia. DEFINITIONS OF TERMS Antioxidant — A substance that inhibits oxidation. Dermatitis — A condition of the skin in which it becomes red, swollen and sore. Results from direct irritation of the skin by an external agent or an allergic reaction. Nerve degeneration — A deterioration of the function or structure of the nerves. ■■ Folate: Needed for synthesis and maintenance of new cells. Found in fortified flour, liver, legumes, nuts and leafy green vegetables. Folate deficiency used to be common in the US and still occurs. People at risk are those with very poor diets, chronic alcoholics and those taking certain drugs. Deficiency affects cells that are actively synthesizing DNA like bone marrow cells. They can’t synthesize enough DNA to divide properly, so they become gigantic – called megaloblastic anemia. ■■ Vitamin B-12: Unique because it’s the only vitamin that is only found in foods of animal origin. Animals either get it from the bacteria they take in while grazing or, if they are ruminants like sheep or cows, they can make it. Poor vitamin B-12 status is fairly common, affecting about 20% of older Americans, usually because of impaired absorption. It results in a severe anemia, nerve degeneration and dementia. Vitamin C: Functions and food sources Everyone has heard of the water-soluble vitamin C. Vitamin C acts as an antioxidant preventing the build up of toxic products from cellular reactions. Most fruits and vegetables contain some vitamin C, but the largest sources are citrus fruits, peppers and green vegetables. An intake of 5 servings of fruit and vegetables a day will provide ample vitamin C. Vitamin C is destroyed by heat, so it must be replaced in pasteurized orange juice. As discussed above, deficiency causes scurvy and alcoholics and those with a poor diet are most at risk for deficiency. Fat-soluble vitamins For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 1.5-6 Figure 16: The beta-carotene in carrots can be converted to vitamin A in your body. Fat-soluble vitamins are absorbed along with dietary fat and are transported in the blood with HDL and LDL cholesterol. Excess fat-soluble vitamins can be stored in fat cells and are not readily excreted, so toxicity is theoretically possible. In practical terms however, toxicity is not common. Fat-soluble vitamins include: vitamins A, D, E and K. Vitamin A: Functions and food sources Vitamin A plays important roles in vision, immune function and making new cells. It is found in beef liver, fish, fish oil, fortified milk and eggs. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 52 LESSON READINGS Vitamin A can also be made in our body from precursors found in certain vegetables’ orange color (like in carrots or squash). Vitamin A has been known for more than 3,500 years as a factor to prevent night blindness – a serious problem in the developing world. People with alcoholism or liver disease are at risk for vitamin A deficiency. Vitamin D: Functions and food sources Vitamin D is critical for bone health, because it is imperative for the absorption of calcium from the diet. Vitamin D also decreases the risk of certain infections and autoimmune diseases like multiple sclerosis. We can synthesize vitamin D from cholesterol if our skin is exposed to the sun. People living in northern latitudes cannot synthesize vitamin D through the winter months because the angle of the sun is too low. The best food sources of vitamin D are fatty fish (sardines, mackerel, herring and salmon) and cod liver oil, as well as fortified milk. Deficiency results in a bone deformity called rickets. People with darker skin pigmentation are at risk for vitamin D deficiency, as well as people that are never or rarely exposed to the sun, including people who always wear sunscreen. Figure 17: These children are all suffering from Rickets caused by a deficiency in vitamin D. Vitamin E: Functions and food sources Similar to vitamin C, vitamin E is an antioxidant that protects against toxic products caused by cell metabolism. Vitamin C will protect against oxidation in the inside of cells where water is present, and vitamin E will give protection in lipid filled parts of cells, like the cell membrane. Vitamin E is found in plant oils, wheat germ, avocado, almonds, peanuts and sunflower seeds. It is very susceptible to heat and will be destroyed if oils are used for deep-frying. Vitamin E deficiency in adults is rare, but people who cannot absorb fat from their intestines are at risk. Vitamin K: Functions and food sources Wo r k b o o k Lesson 1.5-6 Figure 18: Broccoli is a good source of vitamin K. Vitamin K has two important functions: the synthesis and function of blood-clotting factors, and maintaining bone health. The best food sources of vitamin K are leafy green vegetables, broccoli, peas, legumes, fish oils and meat. About 10% of the vitamin K that we absorb comes from bacteria in our microbiome, which produce it. Vitamin K deficiency can occur in newborns because they do not yet have bacteria that synthesize it. This increases risk of hemorrhage; so newborn infants in North America are typically given a vitamin K injection within 6 hours of delivery. 9. Vitamin D is: aa. A hormone. bb. A vitamin. cc. Synthesized from cholesterol. dd. Both A & C. ee. All of the above. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 53 LESSON READINGS Minerals Many minerals are vital to health but like vitamins do not provide energy directly. They do not have complex molecular structures, but are instead simple elements. They are critical to many bodily functions including cell metabolism, transmission of neural messages, growth and development. Typical diets in developed countries contain sufficient amounts of most minerals that either Figure 19: Iodine is often occur naturally or that are added through enrichment and fortificaadded to salt and is a critical tion. Although severe deficiencies are rare in healthy populations, mineral for thyroid function. many people have lower than optimal intakes of some minerals such as calcium, potassium, iron and iodine, and higher than recommended levels of others, such as sodium. Deficiencies of certain minerals remain a major public health concern in less developed countries. Three minerals that you have probably heard of are: ■■ Calcium: Required for healthy bone density, it is also needed for muscle contraction and nerve function because of its role in electrical activity of nerve and muscle cells. Low calcium levels can lead to muscle spasm and twitching, irregular heartbeat, and disorientation. ■■ Potassium: Required for muscle contraction and nerve function because it too is important for the electrical activity of nerve and muscle cells. It is particularly important for the regulation of the heartbeat. Low levels of potassium can lead to muscle weakness or cramping, irregular heartbeat and disorientation. High levels of potassium can be lethal. ■■ Sodium: Required to regulate blood pressure and for nerve function because it too regulates electrical activity. Low levels can lead to a drop in blood pressure, while high levels can lead to elevated blood pressure in some people. Phytonutrients Phytonutrients are an emerging class of micronutrient, but because they are a relatively new discovery not as much is known about them. Two types phytonutrients that you may recognize include: Wo r k b o o k Lesson 1.5-6 ■■ Carotenoids — These phytonutrients give foods their color. For example beta-carotene makes fruits and vegetables orange, lycopene is the red color in tomatoes and watermelon, and lutein is the yellow/green color in leafy greens like kale and spinach. ■■ Polyphenols — A large class of phytonutrients. Resveratrol in grape skin, and EGCG in tea are examples of polyphenols that may act as antioxidants. 10.What is the difference between vitamins and minerals? aa. Our bodies can make vitamins but not mineral. bb. Vitamins are large molecules, minerals are small elements. cc. Vitamins provide energy, minerals do not. dd. You can be deficient in a vitamin, but not a mineral. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 54 LESSON READINGS Phytonutrients have many functions, including acting as antioxidants, enhancing immune function, repairing DNA and detoxifying carcinogens. It is difficult to quantify how many phytonutrients we eat because there is no database listing the amount of each phytonutrient in each food. Additionally, because phytonutrients are nonessential, there is not a recommended intake of these compounds. Figure 13: Flamingos get their pink color from the carotenoids they eat. The more of the carotenoid they eat, the brighter they get! Similarly, eating a lot of orange colored carotenoids can give our skin an orange hue. Wo r k b o o k Lesson 1.5-6 ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 55 STUDENT RESPONSES Most functions of macro- and micronutrients have been discovered when that nutrient was removed from the diet. What kind of information can this type of study give us about that nutrient? What are the limitations to this method of studying the nutrients? _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ ____________________________________________________________________________________________________ Remember to identify your sources _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ Wo r k b o o k Lesson 1.5-6 _____________________________________________________________________________________________________ ___________________________________________________________________________________________ 56 TERMS TERM For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 1.5-6 DEFINITION Alkaline Opposite of acidic. Alkaline describes a substance with a pH greater than 7, demonstrating that it is basic in nature. Alpha bond A chemical bond linking monosaccharides to form disaccharides or a complex carbohydrate that is easily digested. Amino Acid A monomer used to build proteins. Contains a nitrogen-containing amino end, and an acid end. Amino Group A chemical group that contains nitrogen and hydrogen. This group is basic, or alkaline. Amylopectin A type of starch consisting of branched sugar chains Amylose A type of starch consisting of long unbranched sugar chains. Anemia A condition marked by deficiency of red blood cells or hemoglobin in the blood, resulting in fatigue, pale skin and weakness. Antioxidant A substance that inhibits oxidation. Beta bond A chemical bond linking monosaccharides to form disaccharides or a complex carbohydrate that is not easily digested. Carboxyl Group A chemical group that contains carbon, oxygen and hydrogen. This group is acidic. Cellulose An insoluble complex carbohydrate that is the main constituent of plant cell walls. Consists of long chains of glucose monomers. Cholesterol A molecule that contains loops or rings of carbons. Used in cell membranes and to make hormones. Cis A shape of chemical bond where two types of structures lie on the same side of the bond. Will make the bond have the shape of a C, creating a bend in the molecule. Connective Tissue A tissue that connects, supports, binds or separates other tissues or organs. 57 TERMS TERM For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 1.5-6 DEFINITION Dementia A chronic mental disorder marked by poor memory, personality changes and impaired reasoning. Dermatitis A condition of the skin in which it becomes red, swollen and sore. Results from direct irritation of the skin by an external agent or an allergic reaction. Disaccharide Any of the sugars that contain two monosaccharides linked together. Sucrose, lactose and maltose are common disaccharides. Essential Amino Acids An amino acid that is required for life but cannot by synthesized in high enough quantities by the body so it must be consumed in the diet. Essential Fatty Acids Fatty acids that humans cannot make on their own, so must be eaten in the diet. Fat-Soluble Describes a substance that dissolves in fats, not water. Fatty Acids A molecule that is naturally in fats and oils with a long chain of carbons. Fiber An indigestible dietary substance consisting of a large number of sugar monomers joined together by beta bonds. Cellulose and pectin are examples. Glycerol A water-soluble component of triglycerides that connects the three fatty acids together. Glycogen A substance in the liver and some muscles that is a store of carbohydrates. Consists of highly branched sugar chains. HDL High-density lipoprotein. A type of lipoprotein that transports lipids in the blood from tissues and arteries to the liver for processing. Hydrophilic Hydro means ‘water’, Philic means ‘loving’. Having a tendency to mix with or dissolve in water. Hydrophobic Hydro means ‘water’, Phobic means ‘fearing’. Tending to repel or fail to mix with water. Insoluble Fiber Dietary fiber that is not water-soluble. This fiber adds bulk to the diet, preventing constipation. LDL Low-density lipoprotein. A type of lipoprotein that transports lipids in the blood from the liver to tissues and arteries. 58 TERMS TERM For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 1.5-6 DEFINITION Legumes A family of plants with seeds that grow in long cases. Beans, peas and peanuts are legumes. Lipoprotein A group of water-soluble proteins that combine with and transport lipids in the blood. Monomer Mono Means ‘one’, Mer means ‘part’. A molecule that can be bonded to identical molecules to form a polymer. Monosaccharide Any of the sugars that cannot be hydrolyzed to give a simpler sugar. Glucose, fructose and galactose are the monosaccharides. Nerve Degeneration A deterioration of the function or structure of the nerves. Non-Essential Amino Acids Amino acids that can by synthesized by humans. Omega-3 Fatty Acid An unsaturated fatty acid that occurs mainly in fish oils. Contains three unsaturated bonds. Omega-6 Fatty Acid An unsaturated fatty acid that occurs mainly in vegetable oils. Contains two unsaturated bonds. Pectin A soluble gelatinous complex carbohydrate that is present in ripe fruits and is extracted for use in jams and jellies. Peptide A compound consisting of two or more amino acids linked in a chain. These chains of amino acids are shorter than polypeptides. Phytonutrients A substance that is found in certain plants which is believed to be beneficial to human health and prevent various diseases. Unlike vitamins and minerals, phytonutrients are not known to be essential to life. Polymer Poly means ‘many’, Mer means ‘part’. A substance consisting chiefly or entirely of a large number of similar units bonded together. Polypeptide A polymer of a large number of amino acids bonded together in a chain. Forms a protein. Primary Structure The characteristic sequence of amino acids forming a protein or polypeptide chain. Quaternary Structure The structure formed by the interaction of two or more proteins or polypeptide chains. 59 TERMS TERM For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 1.5-6 DEFINITION R Chain A generic name for a side chain on a molecule. In amino acid the R chain can be short or long. Saturated Bond A type of chemical bond that has the maximum number of hydrogens. Secondary Structure The local three-dimensional structure of different portions of a protein or polypeptide chain. Soluble Fiber Dietary fiber that is water-soluble. This fiber type can absorb water and bile in the intestine to form a gel, making you feel full. Starch A carbohydrate consisting of a large number of glucose monomers joined together by alpha bonds. Produced in most green plants as energy storage. Sugar A class of water soluble, crystalline, typically sweet-tasting carbohydrates. Glucose, fructose and sucrose are all sugars. Tertiary Structure The overall three-dimensional structure of a protein or polypeptide chain. Trans A shape of chemical bond where two types of structures lie on opposite sides of the bond. Will make the bond have the shape of a Z, creating a straight molecule. Triglyceride A molecule formed from glycerol and three fatty acids. Triglycerides are the main type of fat found in natural fats and oils, and is the form that fat is stored as in the body. Unsaturated Bond A type of chemical bond in which one or more hydrogens is missing. Water-Soluble Describes a substance that dissolves in water, not fats. 60 Unit 2: Where are we heading? Unit 1: What’s in your food? Unit 2: How does your body use food? Unit 2: Introduction Unit 3: What is metabolic disease? Unit 4: How do I identify ‘good’ and ‘bad’ food? Unit 5: How does this knowledge apply to me? ______________________________________ In Unit 2 we will explore the processes by which the nutrients in food are absorbed and utilized in the body. We will begin with digestion and absorption, and then use biochemistry to understand how the body shuttles energy and nutrients into and out of storage. We will see that the body is in a constant quest to maintain available and adequate levels of blood glucose to nourish the vital functions of the body. 61 LESSON 2.1 WORKBOOK Digestion: From the mouth to the blood stream DEFINITIONS OF TERMS Lumen — The central cavity of a hollow structure in the body. During digestion, food passes through the lumen of each organ in the digestive tract. For a complete list of defined terms, see the Glossary. In Unit 2 we will explore the processes by which the nutrients in food are absorbed and utilized by the body. We will begin with digestion and absorption, and then use biochemistry to understand how the body shuttles energy and nutrients into and out of storage. We will see that the body is in a constant quest to maintain available and adequate levels of blood glucose to nourish the vital functions of our bodies. In this lesson we will review and expand upon your knowledge of digestion and absorption of nutrients. We will describe the process of digestion in each of the main organs, and compare and contrast digestion and absorption of macronutrient rich foods. Digestion breaks polymers into monomers Wo r k b o o k Lesson 2.1 In Lesson 1.5 we learned about the structures of the three macronutrients: carbohydrates, lipids and proteins. We also saw that in most foods macronutrients exist in a larger polymer made of attached smaller monomer units. The polymer forms of macronutrients are too large to be absorbed from the lumens of our intestines. When we eat macronutrients as polymers, a series of steps will break down the polymers to monomers so the macronutrients can be absorbed into our blood, where they become useful to our cells. This process of breaking apart the polymers to monomers is digestion. It is critical that all of the steps of digestion are working properly, otherwise the food that we eat won’t do us any good! 1. Why do we need to digest macronutrients? aa. So they can be easily swallowed. bb. So they are in a small enough form to be absorbed. cc. Monomers are larger than polymers and are not absorbable. dd. Both B & C. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 62 LESSON READINGS Why do we have to digest our food? Our digestive system prepares all of the nutrients in the food that we eat (macronutrients and micronutrients) so they can be absorbed by our bodies and used by our cells. It does this by performing mechanical and chemical processes that digest food, absorbing the nutrients from food and eliminating food waste. To absorb food the body has to do something remarkable: it needs to let nutrients into the body while keeping microbes out. This function is performed by the intestines, which keep microbes out of the body, but let nutrients into the body. One way to do this is to discriminate what gets in based on size, so the intestine only absorbs molecules under a certain size. Hence, you need to break down macronutrients into monomers in order for your body to extract the important nutrients and energy from food. Following food through the gastrointestinal tract Our digestive tract is outside of our body! Figure 1: Organs of the digestive tract. The digestive system is made up of the mouth, esophagus, stomach, and the small and large intestines. While it may seem counter intuitive, nutrients are still considered outside of our body until they are absorbed. This means, even after you swallow your food, it is still outside of your body as it passes through your esophagus, stomach, small and large intestines! Other organs that aid the digestive process, but do not directly interact with the food and nutrients are called accessory organs. These include the liver, gallbladder, pancreas and kidneys. Digestion begins before we even eat our food Wo r k b o o k Lesson 2.1 Food preparation, such as cooking, marinating, pounding and dicing starts the process of digestion by reducing the physical size of the food. Starch granules in food swell as they take up water during cooking, making them easier to digest. You may have seen this when grains like oatmeal or rice get bigger after you boil them in water. Cooking also softens tough connective tissues in meats and fibrous plants. As a result, the food is easier to chew, swallow, and break down. 2. Which of the following is not true about digestion? aa. Monomers must be made into polymers to be absorbed. bb. It makes nutrients more absorbable. cc. It occurs outside of our body. dd. It begins with cooking. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 63 LESSON READINGS Digestion in the mouth DEFINITIONS OF TERMS Amylase — An enzyme that digests starch and glycogen. Bolus — Chemical digestion — Breaking up polymers of food into their respective monomers using chemicals and enzymes. Lysozyme — An anti-bacterial enzyme that destroys the cell walls of certain bacteria. Mechanical digestion — Breaking up food into smaller chunks by force, such as chewing. Peristalsis — Involuntary contractions of the muscles of the esophagus and intestine that create wavelike movements that push the contents of the organ forward. Sphincter — A ring of muscle that creates a one-way valve to guard or close an opening of an organ, such as in the esophagus, stomach and anus. For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 2.1 Throughout digestion there are two types of processing that break down our food: mechanical digestion and chemical digestion. Mechanical digestion happens when we physically grind our food so it becomes smaller. Chemical digestion is when enzymes or chemicals react with the food to break it apart. Both mechanical and chemical digestion occur in the mouth. The teeth tear and grind solid foods into smaller pieces and mix food with saliva. By chewing food, the large pieces that we eat will be broken apart, creating more surface area. This gives important enzymes access to the food to digest it quicker. Saliva contains several substances to aid in digestion, including mucus to lubricate the food, an enzyme called lysozyme to kill bacteria, and enzymes to begin the chemical digestion of food. For example, salivary amylase is the primary enzyme in saliva, which breaks starch amylose into smaller monosaccharides and disaccharides. When food is mixed with saliva, it is called a bolus. The bolus is then swallowed and enters the esophagus. Try this at home: You can test out your own salivary amylase by putting a food containing amylose, like a piece of bread or a cracker, in your mouth without chewing. Your saliva will cover the food and amylase will convert the starch into sugars. You will be able to tell that the amylase is working when the food tastes sweeter. The esophagus brings the bolus to the stomach The esophagus is the muscular tube that extends from the mouth to the stomach. The bolus is moved through the esophagus by gravity and muscular motion called peristalsis. Much like how the muscles in a snake moves food through its body, peristalsis pushes food down the esophagus into the stomach. You can watch a video demonstrating peristalsis through the digestive system online — see this unit on the student website or click below: ■■ Video: What is Peristalsis? Peristal)c Wave Bolus Esophagus Stomach Figure 2: Peristalsis is the muscular movement in the esophagus that moves the bolus from the mouth to the stomach. Before the bolus enters the stomach, it must first pass through a muscular “door” called a sphincter. The opening and closing of sphincters is tightly controlled, and keeps segments of the gastrointestinal tract separated. You can think of sphincters as one way valves. The sphincter dividing the esophagus from the stomach is aptly called the esophageal sphincter. The esophageal sphincter usually prevents the ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 64 LESSON READINGS acidic contents of the stomach from traveling back into the esophagus. If the esophageal sphincter does not function properly, the acidic juices from the stomach can burn the esophagus, causing the symptoms of heartburn. Under some circumstances of chronic heartburn, the acidic stomach contents can even cause lesions in the esophagus, or esophageal ulcers. This condition is called gastroesophageal reflux disease, or GERD, which might be treated with antacids. DEFINITIONS OF TERMS Chyme — The acidic mix of food and gastric juices that passes from the stomach to the small intestine. Denaturation — A process in which the structure of a protein is altered due to exposure to heat or specific chemicals or enzymes. Microvilli — Pepsin — The primary digestive enzyme in the stomach; breaks down proteins into smaller peptide chains. Peptidase — A type of enzyme that breaks peptide chains down into amino acids. Phyloric — Used to describe something that is in the region of the stomach that connects the lower stomach to the small intestine. The stomach grinds and mixes The stomach is essentially a holding and mixing tank because little absorption occurs here – only water and alcohol are absorbed from the stomach. Contractions of the muscular layers of the stomach thoroughly mix food with gastric secretions, transforming the solid bolus into a soupy, acidic mixture called chyme (pronounced 'kime'). Each day, the stomach secretes about 8 cups of gastric juices that aid in digestion. These gastric juices include hydrochloric acid and enzymes that break down proteins. Hydrochloric acid produced in the stomach is very important because it: ■■ Can inactivate hormones and enzymes in foods by denaturing them. This prevents those hormones and enzymes from affecting our bodies’ functions. ■■ Destroys most harmful bacteria and viruses in foods ■■ Breaks dietary minerals free from the foods so that they can be absorbed ■■ Activates an enzyme called pepsin, a peptidase that digests proteins into amino acids. In the name you might notice the ‘—ase’ which refers to an enzyme, and ‘peptid—’, which refers to a peptide. So this is an enzyme that breaks down peptides / proteins. The stomach also secretes a mucus layer that protects the stomach from being digested by its own hydrochloric acid secretions. Heavy use of aspirin and other painkillers can damage the stomach wall because they inhibit the production of mucus. The reduced mucous barrier in the stomach means stomach acid may damage the stomach wall. Villi — A small, elongated projection that increases surface area of the small intestine. For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 2.1 Figure 3: The stomach breaks the bolus into chyme. Absorption of nutrients occurs in the small intestine with help from the accessory organs Figure 4: The villi and microvilli are small, fingerlike projections that line the small intestine. The acidic chyme leaves the stomach and enters the small intestine by passing through the pyloric sphincter. Most digestion and absorption of nutrients occurs in the small intestine. The inside of the small intestine has fingerlike projections called villi and microvilli (as shown in Figure 4). 3. What type of enzyme breaks down proteins? aa. Amylase. bb. Lipase. cc. Peptidase. dd. Sucrase. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 65 LESSON READINGS These projections increase the surface area of the intestinal epithelium so that the nutrients can be thoroughly digested and absorbed. Most digestion occurs in the first half of the small intestine, and requires many secretions from the small intestine itself, as well as the accessory organs, which are the pancreas, liver and gallbladder: ■■ The small intestine secretes enzymes that will break down disaccharides into monosaccharides. DEFINITIONS OF TERMS Bile — A fluid that is created in the liver, and stored in the gall bladder until needed. Bile aids in digestion by making hydrophobic lipids absorbable in water. Electrolytes — Salts and minerals that can conduct electrical impulses in the body. Sodium and potassium are important electrolytes that must be consumed in the diet. Lipase — An enzyme that breaks down triglycerides to fatty acids and glycerol. ■■ The pancreas secretes lipase, the enzyme that will break down lipids, pancreatic amylase to digest amylose, and peptidases to digest proteins. The pancreas also secretes an alkaline mixture to neutralize the acidic chyme so it does not harm the small intestine. ■■ The liver produces bile that is stored in the gallbladder until it is secreted into the small intestine. This acts like dish detergent helping to package lipids into hydrophilic droplets. The small intestine absorbs about 95% of our food energy as protein, carbohydrates, fat and alcohol. The small intestine is also the site of most micronutrient absorption. This absorption occurs by transferring nutrients from the lumen of the small intestine into the intestinal cells, then repackaging the nutrients and releasing them into the blood stream. As we will see later, the liver is the first stop for many nutrients. Final stages of digestion in the large intestine After digestion and absorption occurs, normally only water, some minerals, and undigested food fibers and starches remain to be emptied from the small intestine into the large intestine. It takes about 12-24 hours for a meal to travel through the large intestine. The large intestines have three primary functions: housing bacteria in our microbiome, absorbing water and electrolytes such as sodium and potassium, and forming and expelling feces. Pancreatic amlyase — An enzyme that digests starch and glycogen that is made in the pancreas, and secreted into the small intestine. For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 2.1 Figure 5: Most nutrients are absorbed in the small intestines. Figure 6: Large intestines absorb water and some minerals then expel waste as feces. Recall from Unit 1 that there are two types of dietary fiber: soluble and insoluble. In the large intestine, soluble fiber will absorb extra bile and expel it in our feces. Because bile is made of cholesterol, soluble fiber can actually lower cholesterol levels in our blood by decreasing reabsorption of ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 66 LESSON READINGS bile cholesterol. Both types of fiber become a food source for the bacteria living in our microbiome. These beneficial bacteria in our large intestine synthesize vitamin K, which may then be absorbed from the large intestine into our blood stream. Let's review by looking at digestion and absorption of macronutrient rich foods! DEFINITIONS OF TERMS Lactase — An enzyme that breaks down the disaccharide lactose into one glucose and one galactose monomer. Maltase — An enzyme that breaks down the disaccharide maltose into two glucose monomers. Sucrase — An enzyme that breaks down the disaccharide sucrose into one fructose and one glucose monomer. For a complete list of defined terms, see the Glossary. Now that we have a general idea of the flow of food through the digestive system, let's go into more depth about how each of the three macronutrients are digested and absorbed. Remember, almost all absorption occurs in the small intestine. Carbohydrates are broken down to monosaccharides before absorption The goal of carbohydrate digestion is to break down starch and sugars into monosaccharides. Some carbohydrates begin enzymatic digestion in the mouth by salivary amylase. When food reaches the small intestine, polysaccharides are digested further by pancreatic amylase. Disaccharides are then broken down into monosaccharides by enzymes produced by the small intestines. The type of enzyme that breaks the disaccharide depends on the two types of monosaccharide in the disaccharide. For example: ■■ Maltase acts on maltose to produce two glucose monomers. ■■ Sucrase acts on sucrose (table sugar) to produce glucose and fructose. ■■ Lactase acts on lactose (sugar in dairy) to produce glucose and galactose. Wo r k b o o k Lesson 2.1 Carb-‐rich food Amylase in saliva Polysaccharides Amylase released from pancreas to small intes3nes Disaccharides Enzymes from panacreas to small intes3nes Monosaccharides (Glucose) Absorbed into the body Figure 7: Steps of digestion and absorption of carbohydrates. Once freed, the monosaccharides are absorbed from the intestinal lumen into the blood, where they are transported to the liver. In the liver fructose and galactose are converted into glucose, and glucose is then released into the blood where it is available to the cells of the body. The homeostasis of glucose levels in the blood is highly regulated, a system that we will lean about in great detail over the next lessons of this unit. 4. Carbohydrates are absorbed as: aa. Fiber. bb. Monosaccharides. cc. Disaccharides. dd. Glucose. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 67 LESSON READINGS Lipids are emulsified by micelles and transported in the lymphatic system Dietary Fat DEFINITIONS OF TERMS Chylomicron — A lipoprotein that carries dietary fat through the lymphatic system to the blood. Gastric lipase — An enzyme that breaks down triglycerides that is produced in the stomach. Lingual lipase — An enzyme that breaks down triglycerides that is produced in the mouth. This enzyme is active in infants, but loses activity in adults. Lymphatic system — A network of vessels through which fluid containing white blood cells is transported throughout the body. Micelle — A vesicle used to transport lipids that has a hydrophilic exterior and a hydrophobic interior. Pancreatic lipase — An enzyme that breaks down triglycerides that is produced in the pancreas and secreted into the small intestine. For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 2.1 Similar to carbohydrates, digestion of lipids begins in the mouth by the activity of lingual lipase. This enzyme only plays a minor role in fat digestion in adults, but is active in infancy when it is used to break down the fats in breast milk. Some lipid digestion also occurs in the stomach by the enzyme gastric lipase, but the majority of lipid digestion occurs in the small intestine. The presence of fat in the small intestine stimulates the release of bile from the gallbladder and pancreatic lipase from the pancreas. Bile emulsifies fats, meaning that it breaks fat into many tiny droplets called micelles, and forms a shell around the micelles that keep the fat droplets suspended in water-based intestinal contents. This process increases the surface area of lipids and allows pancreatic lipase to efficiently break down triglycerides into free fatty acids (see Figure 8). Figure 8: Bile emulsifies fats into micelles, increasing the surface area of lipids and allowing pancreatic lipase to break triglycerides into free fatty acids. The lipid portion of the micelles is absorbed by the intestinal cells of the small intestine, this is where about 95% of dietary fat is absorbed. Because lipids are large structures, they cannot be absorbed directly into the blood stream like amino acids or monosaccharides. Instead, lipids are absorbed into the lymphatic system in a lipoprotein called chylomicrons. Chylomicrons are similar to other lipoproteins like HDL and LDL cholesterol, and have a hydrophilic exterior and a hydrophobic interior so that they can transport lipids in the water-based blood and lymphatic system. The chylomicrons will eventually enter the blood stream, where they will be transported to the liver for repackaging. The fat-soluble vitamins are also absorbed from the small intestine with the lipids in these chylomicrons. Proteins are digested into amino acids Enzymatic digestion of protein begins in the stomach with the secretion of hydrochloric acid. This acid will denature, or unravel, proteins. As we already learned, pepsin is an enzyme secreted in the stomach and breaks down long polypeptide chains into shorter chains of amino acids. The partially digested proteins then move from the stomach into the small intestine, where the pancreas secretes other peptidases to further breakdown the peptide chains into amino acid monomers. The amino acids are absorbed into the cells of the small intestine, and then travel via the blood to the liver for use in protein synthesis, energy needs, conversion to carbohydrate or fat, or release into the blood for transport to other cells. 5. Micelles are: aa. Made of bile. bb. Hydrophilic. cc. Hydrophobic. dd. All of the above. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 68 STUDENT RESPONSES Each step of digestion presents a potential complication. For example, someone that has had a stoke may have difficulty swallowing their food so they have to cut their foods into small pieces. What would be the consequences of having too little, or too much stomach acid? What sort of symptoms would this person have? How would the digestion and absorption of the macronutrients and micronutrients change? _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ Remember to identify your sources _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ ____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ Wo r k b o o k Lesson 2.1 _____________________________________________________________________________________________________ ___________________________________________________________________________________________ 69 TERMS TERM For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 2.1 DEFINITION Amylase An enzyme that digests starch and glycogen. Bile A fluid that is created in the liver, and stored in the gall bladder until needed. Bile aids in digestion by making hydrophobic lipids absorbable in water. Chemical Digestion Breaking up polymers of food into their respective monomers using chemicals and enzymes. Chylomicron A lipoprotein that carries dietary fat through the lymphatic system to the blood Chyme The acidic mix of food and gastric juices that passes from the stomach to the small intestine. Denaturation A process in which the structure of a protein is altered due to exposure to heat or specific chemicals or enzymes. Electrolytes Salts and minerals that can conduct electrical impulses in the body. Sodium and potassium are important electrolytes that must be consumed in the diet. Gastric Lipase An enzyme that breaks down triglycerides that is produced in the stomach. Lactase An enzyme that breaks down the disaccharide lactose into one glucose and one galactose monomer. Lingual Lipase An enzyme that breaks down triglycerides that is produced in the mouth. This enzyme is active in infants, but loses activity in adults. Lipase An enzyme that breaks down triglycerides to fatty acids and glycerol. Lumen The central cavity of a hollow structure in the body. During digestion, food passes through the lumen of each organ in the digestive tract. Lymphatic System A network of vessels through which fluid containing white blood cells is transported throughout the body. Lysozyme An anti-bacterial enzyme that destroys the cell walls of certain bacteria. Maltase An enzyme that breaks down the disaccharide maltose into two glucose monomers. Mechanical Digestion Breaking up food into smaller chunks by force, such as chewing. 70 TERMS TERM For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 2.1 DEFINITION Micelle A vesicle used to transport lipids that has a hydrophilic exterior and a hydrophobic interior. Microvilli Even small than the villi, microvilli are projections that cover the villi Pancreatic Amylase An enzyme that digests starch and glycogen that is made in the pancreas, and secreted into the small intestine. Pancreatic Lipase An enzyme that breaks down triglycerides that is produced in the pancreas and secreted into the small intestine. Pepsin The primary digestive enzyme in the stomach; breaks down proteins into smaller peptide chains. Peptidase A type of enzyme that breaks peptide chains down into amino acids. Peristalsis Involuntary contractions of the muscles of the esophagus and intestine that create wavelike movements that push the contents of the organ forward. Pyloric Used to describe something that is in the region of the stomach that connects the lower stomach to the small intestine. For example, the pyloric sphincter is the sphincter between the stomach and the small intestine. Sphincter A ring of muscle that creates a one-way valve to guard or close an opening of an organ, such as in the esophagus, stomach and anus. Sucrase An enzyme that breaks down the disaccharide sucrose into one fructose and one glucose monomer. Villi A small, elongated projection that increases surface area of the small intestine. 71 LESSON 2.2 WORKBOOK Metabolism: Glucose is the middleman for ATP DEFINITIONS OF TERMS Homeostasis — The tendency toward a relatively stable equilibrium that is maintained by physiological processes. In Lesson 2.1 we discussed the digestion and absorption of nutrients. After the nutrients are absorbed, what are they used for? In this lesson we will discuss the process by which energy is made from the macronutrients. We will identify the steps in glucose metabolism that are important in the production of ATP, and explore why it is so important to maintain blood glucose homeostasis. Glucose For a complete list of defined terms, see the Glossary. Metabolism makes the macronutrients useful In Lesson 2.1 we learned that the monomer forms of the macronutrients are the forms that can be absorbed in the small intestine. Once the macronutrients reach the liver, metabolism takes those monomers and breaks them down into even simpler forms that have two main functions: they can become building blocks for cellular structures or they can be used to make the ATP that cells use for energy. Macronutrients are metabolized in the liver Wo r k b o o k Lesson 2.2 After being absorbed in the small intestines, carbohydrates, lipids and proteins travel in the blood to the liver. Over the next series of lessons you will see that the liver is the master regulator of metabolism. The liver is often referred to as the biochemist of the body because it can perform chemical reactions that other tissues cannot. For example, the liver stores glucose as glycogen, repackages fatty acids for storage and makes new amino acids. The liver is also the primary organ for making new glucose, which is a very important job. In fact, the liver is the only organ that can make macronutrients from other macronutrients. Because of this, the liver plays a central role in maintaining a constant concentration of glucose in the blood stream. This is important because the brain and the red blood cells can only use glucose for energy! ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 72 LESSON READINGS The energy in macronutrients is shuffled through many forms to generate ATP The release of energy from macronutrients involves breaking chemical bonds because that is where the energy is stored. Different types of bonds contain different amounts of energy, remember it is the combustible energy in the macronutrients that is used to derive calories. As bonds in the macronutrients are broken the energy is released and recaptured into a new chemical bond that is the universal fuel source of all cells, ATP. So, the end goal of metabolism is to put the energy from the bonds of the macronutrients into the energy in the bonds of ATP. DEFINITIONS OF TERMS ATP — The molecular unit of energy used by all cells in the body. For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 2.2 ATP is the energy source for our cells For the energy in macronutrients to be used in cellular activities the combustible energy in the carboncarbon bonds is transferred to a compound called adenosine triphosphate (ATP). ATP and its related compounds ADP (adenosine diphosphate) and AMP (adenosine monophosphate) are the key energyproducing molecules used by cells. As shown in Figure 1, one molecule of ATP consists of High Energy the nucleoside adenosine and three phosphate Phosphate Bonds! groups. The phosphate groups are negatively charged and don’t like being close to one another, therefore the bond connecting the phosphates has a lot of energy. You can think of this like Phosphate Groups! magnets: if you have two strong magnets and Adenosine! hold them close to each other they’ll either snap together or repel one another. Now imagine the strength it takes to force the magnets together while they are repelling each other – this is what the bonds holding the phosphate groups together is doing. These bonds are extremely high energy, and when they break energy is released. Cells use the high energy in the phosphate bonds to Figure 1: The molecular structure of ATP: catalyze vast numbers of enzymatic reactions the energy of ATP is stored in the bonds required for life. For example, energy from ATP is connecting the phosphate groups. When required to make new amino acids in the liver. those bonds are broken, energy is released. 1. The type of energy stored in chemical bonds is: aa. Thermal energy. bb. Electrical energy. cc. Potential energy. dd. Combustible energy. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 73 LESSON READINGS From glucose to ATP DEFINITIONS OF TERMS Acetyl CoA — A molecule that shuttles carbons to the citric acid cycle. Citric acid cycle — A cycle of reactions used to generate energy that takes place in the mitochondria. Any cell that has mitochondria can do this. Electron transport chain — A chain of proteins that transfers protons from hydrogen across a membrane, keeping them separate from electrons. The energy released at the end of the chain is used to generate ATP. Glycolysis — The breakdown of glucose to produce energy. NADH — A molecule that shuttles hydrogens into the electron transport chain. Pyruvate — A molecule created from glucose and some amino acids. For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 2.2 How does the energy from ATP relate to the calories in a food? When the macronutrients we eat are digested down to sugars, amino acids and fatty acids they can then be used to produce ATP, which is maintained in all cells until needed. The homeostasis of blood glucose is important because ATP can’t travel in the blood, so glucose is the middleman passed between cells and used to synthesize ATP. Every cell in the body conducts glycolysis, a process used to convert glucose to acetyl CoA, and almost every cell can then use the acetyl CoA in the citric acid cycle and the electron transport chain to make more ATP. Additionally, only particular organs can use fatty acids or amino acids to produce ATP, while all cell types use glucose. Don't be alarmed by all the new terms here, we will be seeing them again! Mitochondria are the energy factories of the cell You may remember that mitochondria are organelles located within cells. What is important about the mitochondrion is that it has two membranes: an inner membrane and an outer membrane. Because of this, the mitochondria can keep steps in metabolism separated. We will see Inner Membrane! Inner Membrane! how separating molecules is important more when we discuss the electron transport chain. The mitochondrion is the location for the citric acid cycle, the electron transport chain and breakdown Outer Membrane! Outer Membrane! of fatty acids for energy, meaning that every cell that has mitochondria can participate in those reactions. Red Figure 2: By having both an outer and an inner membrane, the mitochondria can keep certain blood cells do not contain mitochondria, molecules and reactions separate. and therefore can only use glycolysis for energy. Glycolysis: Converting glucose to acetyl CoA The first steps of glucose metabolism occur in the cytosol of cells, and are called glycolysis (glycolysis means ‘breaking down glucose’). As you can see on the next page in Figure 3, the six carbons (shown in blue) of glucose are converted into two pyruvate molecules, each containing three carbons. Because energy is stored in the carbon bonds, breaking the glucose into two pieces releases energy, resulting in the production of two molecules of ATP. Glycolysis also produces a molecule called NADH, an energy intermediate used to make ATP in the electron transport chain. 2. ATP is: aa. Generated in the mitochondria. bb. Used by all cells except the brain and red blood cells. cc. Absorbed from the foods that we eat. dd. Easily transported in the blood. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 74 LESSON READINGS The two pyruvates are shuttled into the mitochondria where one more carbon is removed, resulting in acetyl CoA and another NADH. As we will see in this unit, acetyl CoA is an important molecule that is at the crossroads of glucose metabolism, fatty acid metabolism and amino acid metabolism. Glucose! Glycolysis! Pyruvate! Acetyl CoA! What does breathing have to do with metabolism? Carbon! Citric Acid Cycle! As carbons are removed in metabolism, they Energy Released! exit the cell as carbon dioxide (CO2), and we eventually breathe it out. If we were to hold Figure 3: In glycolysis glucose is converted into acetyl CoA, which is transported into the our breath for too long, the CO2 would build mitochondria where it goes into the citric acid up in our blood and become toxic. Additioncycle. ally, breathing brings in fresh oxygen that is needed for metabolism to occur. The citric acid cycle and the electron transport chain are both aerobic processes, meaning that they require oxygen. In times when we are not breathing quickly enough, like in exercise, the citric acid cycle cannot occur. Our brain is the organ that is the most sensitive to oxygen deprivation, and even a short time without breathing in oxygen can have detrimental effects to our nervous system. Acetyl CoA is shuttled into the citric acid cycle in the mitochondria Wo r k b o o k Lesson 2.2 Figure 4: NADH and FADH2 work like delivery trucks, shuttling hydrogen from water to the electron transport chain. The major way energy released by glucose metabolism intersects with the electron transport chain is via the citric acid cycle, which takes place in the mitochondria. When acetyl CoA enters the mitochondria and participates in the citric acid cycle, it first joins with four other carbons (see Figure 3 above). Subsequently, the carbon bonds are broken down releasing energy. That energy is used to transfer a hydrogen ion from water to NAD+, forming NADH, as shown in Figure 5. Similarly, two hydrogen ions can be added to FAD to make FADH2. NADH and FADH2 work like delivery trucks, taking hydrogen from water and delivering to the next step in metabolism: The electron transport chain. 3. Acetyl CoA is: aa. Made out of carbons and a B-vitamin. bb. The molecule that connects glucose, amino acid, and fatty acid metabolism. cc. The form in which energy is stored in cells. dd. Both A and B. ee. All of the above. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 75 LESSON READINGS At the end of one turn of the citric acid cycle, 3 NADH, 1 FADH2 and only 1 ATP are produced. The NADH and FADH2 are then used in the electron transport chain to produce 9 additional ATP. The electron transport chain is critically important because it provides 90% of the ATP obtained from the metabolism of glucose. 1) Carbons bonded together" 2) A bond is broken, releasing energy" 3) That energy is used to remove a hydrogen from water and place it on NAD NAD+" Figure 5: Energy is transferred from the bonds holding carbons together to the bond attaching hydrogen to NAD+. Final steps: The electron transport chain Outer Membrane! H + H + H + H + Inner Membrane! -‐ -‐ -‐ -‐ ADP ! ATP! Figure 6: The positive protons of hydrogen (H+) and the negative electrons (-) are kept separate in the electron transport chain until the end, where the protons go down their energy gradient to make ATP, using the enzyme ATP synthase. Wo r k b o o k Lesson 2.2 Each hydrogen that is added to NAD+ and FAD contains one proton and one electron. The positively charged proton, and the negatively charge electron are highly attracted to one another, and prefer to be kept close. In the electron transport chain the protons and electrons from the hydrogen are split apart and kept separate by the membranes of the mitochondria, as shown in the figure to the left. Once separated the attraction of the proton and electron create a 'pressure'. We can again use the idea of magnets to think of the energy in the electron transport chain. The negative electrons and positive protons are like strong magnets that are attracted to one another. A great amount of effort is required to separate the two, and when you bring them near one another they snap back together. The inner mitochondrial membrane is what is used to keep the protons and electrons separated until the last step of the electron transport chain, where the protons are allowed to travel through a channel in an enzyme called ATP synthase. 4. Which of the following is NOT true about the citric acid cycle? aa. It takes place in the mitochondria. bb. It requires oxygen. cc. It creates NADH and FADH2. dd. All cells can do it. 5. Which of the following would prevent the electron transport chain from functioning? aa. If ATP levels were too low. bb. If no glucose was available to the liver. cc. If the protons were not kept seperate from the electrons. dd. If too much NADH is produced. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 76 LESSON READINGS DEFINITIONS OF TERMS Brown adipose tissue — A type of adipose tissue that is abundant in newborns and hibernating mammals. It generates body heat in animals that do not shiver. For a complete list of defined terms, see the Glossary. ATP synthase is an enzyme that can harness the energy released as the protons and electrons are allowed to rejoin, and uses that energy to add a phosphate group onto ADP, creating new ATP. You can think of ATP synthase as a water turbine: the protons trapped in the inter-membrane space are Figure 7: Protons move though ATP synthase and drive like water trapped in a dammed the production of ATP like a turbine collects energy from off lake. Once the dam is opened, water flowing through a hydroelectric power plant. the water flows out of the lake and moves a water turbine. This movement of the water turbine generates electricity for us to use. Similarly, as the protons are allowed to flow through the ATP synthase channel the energy actually rotates a part of ATP synthase, generating energy to make new ATP. Brown fat tissue uses the electron transport chain to keep us warm! If the energy that is released as the protons flow back to their electrons is enough to maintain the energy needs of our cells, what would happen if the energy was not redirected into ATP? There is a type of fat tissue called brown adipose tissue that is highly concentrated with mitochondria. In these mitochondria a separate channel exists other than ATP synthase that lets protons rejoin the electrons. Instead of producing ATP, this channel lets the energy be released as heat, raising body temperature. Babies have higher concentrations of brown adipose tissue than adults, and are used to keep the infants warm. Additionally, people living in colder climates may have more brown adipose tissue than people in warm climates. Figure 8: People living in cold climates have extra brown fat to keep the body warm. How the liver keeps blood glucose levels constant Wo r k b o o k Lesson 2.2 ATP cannot be transported in the blood, so each cell in your body must produce its own ATP. To do this, a constant supply of glucose must be available in the blood, especially for the brain and the red blood cells that can only use glucose for energy! The liver can supply new glucose to the blood, and the muscles and adipose tissue can provide amino acids and fatty acids. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 77 LESSON READINGS 6. Glucose is the only type of nutrient used to release energy: aa. True. bb. False. Acetyl CoA shuttles carbons between cycles If glucose levels were low and no glucose became available in the blood your brain would shut down! The body must call upon other nutrients – fats and proteins, to supply the glucose or glucose-like compounds it needs. Conversely, in times of plenty the body stores away excess nutrients as fat and as protein to call upon later. At the crossroads of this whole process is acetyl CoA. Glucose, fatty acids and amino acids all interact with acetyl CoA, the consequences of which will depend on the energy requirements of the cell at that time. Acetyl CoA can either direct metabolites into energy producing, or energy storing, pathways. Releasing energy from fat Wo r k b o o k Lesson 2.2 Figure 9: Acetyl CoA is the crossroads between glucose, fatty acids and amino acids. Just as cells release energy from carbohydrates and trap it as ATP, they also release and trap energy from triglycerides. Recall that triglycerides are molecules formed by the combination of fatty acids and glycerol. During periods of low calorie intake or fasting the triglycerides are broken down into fatty acids and glycerol. Carbons are cut off of fatty acids, two at a time, and can be made into acetyl CoA. Acetyl CoA then enters the citric acid cycle to produce NADH and FADH2 to be used in the electron transport chain as discussed above. Because fatty acids have a lot more carbons Fatty Acid (Palmitate)! than a molecule of glucose, they can be used to make more ATP than glucose can. Additionally, the process of breaking off the x 8! Acetyl CoA! 2-carbon fragments from fatty acids releases one NADH and one FADH2 molecule, so for every 2-carbon fragment that is shuttled Carbon! Citric Acid Cycle! through the citric acid cycle, the Amino Group! total yield is 14 ATP. Palmitate Energy Released! is a common fatty acid found in palm oil, and contains 16 carbons (Figure 10). Therefore, metaboAmino Acid! lism of palmitate would yield 108 molecules of ATP! Figure 10: Fatty acids provide acetyl CoA for the citric acid cycle, but completing the cycle also required amino acids. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 78 LESSON READINGS Releasing energy from amino acids Protein is the other energy-containing macronutrient, however it is rarely used to produce energy. Amino acids are usually used to produce the proteins the body needs. In starvation when glycogen stores are depleted, some amino acids can be used to make energy by breaking apart their carbon bonds to make pyruvate, acetyl CoA, or other intermediates in the citric acid cycle, depending on the shape of the amino acid. Figure 11 shows some amino acids being used in the citric acid cycle. Carbon! Amino Group! Energy Released! Citric Acid Cycle! Amino Acid! Figure 11: Amino acids can enter the citric acid cycle once their amino groups are removed. How are the micronutrients involved? Vitamins and minerals have numerous functions in the human body, ranging from bone structure to immune function. They also play an important role in metabolism. Vitamins and minerals are required for many metabolic pathways. For example, the B-vitamins (thiamin, riboflavin, niacin, pantothenic acid, biotin, vitamin B6, folate, and vitamin B-12) as well as iron and copper are required for acetyl CoA to function. Some of the key players in metabolism that we discussed today are made from the B-vitamins: the CoA part of acetyl CoA is synthesized from pantothenic acid, NADH is made from fiacin, and FADH2 is made from riboflavin. People that have a deficiency in one or more of these vitamins cannot readily make ATP, and can become fatigued and have neurological disorders. Wo r k b o o k Lesson 2.2 ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 79 STUDENT RESPONSES Dinitrophenol (DNP) is a chemical that was sold as a diet pill in the first half of the 1900’s. DNP prevents the mitochondria from being able to separate protons and electrons. Why would this cause someone to lose weight? Can you guess why this drug is no longer allowed? _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ Remember to identify your sources ____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ Wo r k b o o k Lesson 2.2 _____________________________________________________________________________________________________ ___________________________________________________________________________________________ 80 TERMS TERM For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 2.2 DEFINITION Acetyl CoA A molecule that shuttles carbons to the citric acid cycle. Brown Adipose Tissue A type of adipose tissue that is abundant in newborns and hibernating mammals. It generates body heat in animals that do not shiver. Citric Acid Cycle A cycle of reactions used to generate energy that takes place in the mitochondria. Any cell that has mito chondria can do this. Electron Transport Chain A chain of proteins that transfers protons from hydrogen across a membrane, keeping them separate from electrons. The energy released at the end of the chain is used to generate ATP. Glycolysis The breakdown of glucose to produce energy. Homeostasis The tendency toward a relatively stable equilibrium that is maintained by physiological processes. NADH A molecule that shuttles hydrogens into the electron transport chain. Pyruvate A molecule created from glucose and some amino acids. 81 LESSON 2.3 WORKBOOK Part one: Glucose homeostasis in the blood – storing energy Glucose metabolism takes place in all cells to make ATP. The liver plays an important role in regulating the levels of glucose in the blood so that the brain has enough glucose to metabolize. In the next two lessons we will focus on the question: How does the liver regulate levels of glucose in the blood? In this lesson we focus on the metabolic pathways the liver uses to shuttle the energy from nutrients into storage as glycogen, fat, and protein. Extra glucose in the blood In the previous lesson we learned about the importance of glucose for cells in the body, and that a constant supply of glucose is needed in order for cells to make ATP for survival. Glucose can be transported in the blood, but ATP can’t, so each cell in your body is relying on a steady supply of glucose in order to build ATP. If blood glucose levels get either too high or too low, the cells cannot function properly. Because of this, our organs have developed a system for maintaining steady blood glucose levels, called glucose homeostasis. Why is glucose homeostasis important? Wo r k b o o k Lesson 2.3 What would happen if blood glucose levels were not maintained? The goal of glucose homeostasis is to deliver glucose to the cells so they can function. The brain uses 60% of the glucose that we take in through our diets. The majority of the remainder is used to maintain body temperature, move blood, contract muscles and maintain cells and tissues. Given that most cells and tissues utilize more nutrients than they can store between meals, there needs to be a source of nutrient delivery to the cells. The blood stream is the buffet table that maintains a constant supply of nutrients for cells. Without this steady supply of nutrients cells cannot function, and if left without nutrients for too long the cells will die. 1. The purpose of glucose homeostasis is: aa. To ensure glucose concentrations do not get dangerously high. bb. To ensure glucose concentrations do not get dangerously low. cc. To give tissues a constant supply of glucose. dd. All of the above. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 82 LESSON READINGS In some cases, like in diabetes, blood glucose concentrations will get too low or too high for a long period of time. A sudden, sharp drop in blood glucose concentrations can even result in loss of consciousness or coma because the brain is deprived of the energy it needs from glucose. To the contrary, high blood glucose can cause damage to nerves and impairs the body’s ability to heal wounds, which can lead to ulcers or in some cases amputation. What causes blood glucose to rise and fall? Glycemic index (GI) — A system of ranking foods based on their effect on blood glucose concentrations. For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 2.3 BLOOD GLUCOSE LEVELS DEFINITIONS OF TERMS If all of our organs are functioning properly, the amount of glucose that is entering the blood GI High stream depends entirely on what and when your last meal was. As we saw in Lesson 2.1, simple sugars are easily digested and absorbed in our intestines because they GI Low are already in the monomer form; simple sugars get into our blood stream quicker than complex carbohydrates like starches that 1 2 need rise to a spike in blood glucose levels. TIME / HOURS If you eat a food that contains both simple sugars along with complex carbohydrates, proteins or lipids, the simple sugars will get Figure 1: Foods with a lot of simple sugars tangled up with the harder-to-digest parts of have a high glycemic index (GI) because they the food, and the amount of glucose in your cause spikes in blood glucose. Foods with fiber, protein and lipids have a low GI. blood won’t spike quite as much. Foods that cause a rapid spike in blood glucose, followed by a sharp drop in blood glucose are said to have a high glycemic index (GI). Contrarily, foods that cause a slow, steady rise in blood glucose after they are eaten have a low glycemic index. You can see both patterns of blood glucose levels in the figure to the right. Sharp spikes in blood glucose will be sensed by the pancreas, which will respond by sending signals to quickly clear the blood of the extra glucose. Quick spikes and drops in your blood glucose will make you feel hungrier than a steady rise and decline in blood glucose. This is why you will still feel hungry after you drink a can of soda, but you would feel full Figure 2: if you ate the same amount of calories from a piece of fruit that contains fiber. Soda has a high glycemic index (GI). 2. Which of the following would cause a rapid spike in blood glucose after eating it? aa. An apple. bb. A turkey sandwich. cc. A diet soda. dd. A glass of orange juice. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 83 LESSON READINGS 3. Which of the following is NOT normally a way that extra glucose in the blood is used? aa. It is excreted in the urine. bb. It is stored as triglycerides. cc. It is stored as glycogen. dd. It is turned into amino acids. Diabetes is characterized by high blood glucose concentrations DEFINITIONS OF TERMS Adipose — A type of cell or tissue that is used by the body for the storage of fat. For a complete list of defined terms, see the Glossary. Normally, when blood glucose levels are high the body reacts by storing the glucose to use later. If blood glucose levels are left high for too long it can actually cause damage to cells and tissues because the glucose will stick to proteins, changing their function. In diabetes, the normal signals that tell the body to store glucose for later use malfunction, resulting in high blood glucose levels. One of the tests that doctors will conduct to determine if a person has diabetes is testing the amount of glucose in the urine. Normally, glucose is used or stored up by the body and does not get into the urine, but in a diabetic person the extra blood glucose is secreted in the urine. We will learn more about the causes and consequences of diabetes in Unit 3. Figure 3: High levels of glucose in the urine may indicate diabetes. Storing extra glucose After you eat, nutrients are absorbed and are transported by the blood. Cells will pull the amount of glucose they need out of the blood, and the extra glucose will be stored for later use. This prevents blood glucose levels from remaining high for too long, which in turn prevents the impairment of cellular functions. For the remainder of this lesson we will explore the steps of energy storage in the each of the key organs. In general, the body stores most of its energy in a calorie dense form – fat! 4. How do tissues know that it is time to store glucose, instead of use glucose? aa. Each tissue can sense blood glucose concentrations. bb. The brain sends messages to the tissues. cc. Insulin released from the pancreas sends messages to the tisues. dd. The liver sends messages to tissues. The pancreas and liver work together to keep blood glucose concentrations constant Wo r k b o o k Lesson 2.3 The pancreas and the liver are two important organs in glucose homeostasis. If we go back to our idea of the blood being a buffet table of nutrients, the pancreas is the wait staff constantly checking the table to make sure that there is the right amount of food on the table at all times, and the liver is the head chef that is busy making the food and sending it out. If there is High%Blood%Glucose% Insulin%Signals%the%Liver% more glucose in the blood than Promotes%Insulin%Release% %to%Store%Glucose%% what is needed by the cells, the pancreas will sense this and send a message in the form of insulin, Insulin% telling the liver to package the glucose for storage. These messages also go to the storage Pancreas( Liver( facilities: adipose (fat) cells store Figure 4: High levels of glucose stimulate the pancreas to triglycerides and muscle tissue make insulin that signals the liver to store glucose. stores glycogen. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 84 LESSON READINGS Quick limited storage: Glycogen DEFINITIONS OF TERMS Lipogenesis — The metabolic formation of fat. For a complete list of defined terms, see the Glossary. The first storage tanks that get filled up are the glycogen stores. As you recall from Unit 1, glycoGlycogen Glucose gen is a long, heavily branched chain of glucose monomers. Glycogen is only stored in the Glycogen muscles and the liver, and the amount of storage is limited, so every time you eat you probably fill up your glycogen stores. We typically only have room to store up to 18 hours' worth of glucose as Figure 5: The liver and muscles can store glycogen, and these stores are depleted quicker extra glucose as glycogen, which provides a if you exercise. Because glycogen has so many quick source of glucose when needed. branches, it can be broken down easily, resulting in the quick release of glucose. The glycogen stored in the muscles is the quick source of energy when you are exercising, and the glycogen stored in the liver ensures that glucose can be released into the blood when needed for the brain (the liver is the only organ that can release glucose, so glycogen in the muscle can only provide glucose to that muscle). When blood glucose levels are high, insulin is released from the pancreas which sends a message to the liver and the muscle to store glucose as glycogen. Long term unlimited storage: Fat Wo r k b o o k Lesson 2.3 Acetyl CoA is the important intermediate in the conversion of extra glucose to fat. Remember that during glycolysis glucose is broken down into two molecules of acetyl CoA. When the body has enough ATP, it no longer needs to feed the acetyl CoA into the citric acid cycle. Instead, the acetyl CoA is used to build the fatty acid tails of triglycerides, which are then stored in adipose tissue until needed. The process of making lipids is called lipogenesis. Lipogenesis occurs in the liver, and the triglycerides are then packaged up into the cholesterol lipoprotein called LDL to be sent to other tissues for use or storage. Remember that fatty acids Glucose Acetyl CoA Citric acid cycle Fat (Triglyceride) Adipose stores fat Lipogenesis Figure 6: If you have too much glucose you may store the energy as fat in a process called lipogenesis. Only the liver can make fat from glucose, and it is stored in adipose tissue. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 85 LESSON READINGS Fa#y Acids Cytoplasm Nucleus Figure 7: Adipose cells can store a practically unlimited amount of fatty acids. are simply long, straight chains of carbons, so they are easily packed together tightly. Also, because of the large number of carbon bonds, fatty acids are a densely packed source of combustible energy. The triglycerides are bundled up and stored in adipose tissue, or fat tissue. Men tend to store this fat in their bellies, whereas women are more likely to store fat in their hips and thighs, although every person is unique. Our fat stores can expand to make room for new triglycerides, meaning that we have essentially an unlimited capacity to store fat, whether we like it or not! The soda to fat expressway Fructose is the simple sugar that is in fruits, honey and high fructose corn syrup. Naturally occurring fructose in fruits is usually bound up with the fiber of the fruit, making the absorption slow. In food products with corn syrup and high fructose corn syrup, the fructose is free to be easily absorbed. In fact, fructose is more easily absorbed than glucose and once absorbed, fructose is normally converted into glucose in the liver. However, when eaten in high amounts the fructose may be more readily converted into triglycerides than glucose. This is because the use and packaging of fructose is not as highly regulated as glucose, so it is more likely that you have an overload of fructose in the liver than glucose. We tend to eat more fructose in our diets now than ever before, and some scientists think that this increase in fructose consumption is a contributing factor in the rise of obesity rates. Figure 8: High fructose corn syrup is rapidly absorbed by the body. Making amino acids Wo r k b o o k Lesson 2.3 Although glucose isn’t converted into amino acids as a way to store it as energy, several amino acids can be made from glucose. Recall from Unit 1 that there are two types of amino acids in our body: essential and non-essential. Essential amino acids are those that we must eat in our diet because the cells in our body cannot make enough of them. In contrast, non-essential amino acids require proper nutritional intake of the starting components for amino acid synthesis. In fact, eating enough essential amino acids is necessary for the synthesis of some of the non-essential amino acids. 5. All amino acids are made from glucose in the liver. aa. True. bb. False. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 86 LESSON READINGS Cells in the liver make non-essential amino acids from intermediates of glycolysis and the citric acid cycle. When glucose is converted to acetyl CoA in glycolysis it goes through several steps of intermediate molecules. Similarly, in the citric acid cycle there are many intermediate molecules that transfer the carbons from one another. In times when a lot of glucose is available, such as after a meal, liver cells can use the intermediates of glycolysis and the citric acid cycle to make amino acids instead of ATP. This is important because proteins have many key functions in the body: ■■ Produce vital body structures: Proteins are the structural support of cells and tissues. ■■ Acid/base balance: Amino acids can be acidic or basic and act as a buffer to keep the body pH within a narrow range. Glucose Acetyl CoA Non-‐essen0al Amino acids Citric acid cycle Figure 9: The liver can make the non-essential amino acids from intermediates in glycolysis and the citric acid cycle. These amino acids are then delivered to other cells through the blood. ■■ Forming hormones, enzymes and neurotransmitters: Amino acids are required to synthesize most of the hormones in the body. ■■ Immune function: Antibody proteins are a key component of immune function. Without sufficient dietary protein, the immune system cannot build its antibody defense. ■■ Transporting nutrients: Many proteins carry nutrients through the bloodstream to cells and across cell membranes to sites of action (like the proteins working with fats in HDL and LDL). A quick review of today’s material Wo r k b o o k Lesson 2.3 The figure to the right orients us to where all of the processes we’ve discussed today are occurring. After eating a meal, nutrients are digested and absorbed from the gastrointestinal tract into the blood. The pancreas senses an increase in blood glucose concentrations and secretes insulin. The insulin sends signals to other tissues in the body: in the liver, insulin promotes the repackaging of nutrients for storage; in the muscles insulin stimulates the absorption and storage of glucose as glycogen; in the adipose tissue insulin facilitates the storage of fatty acids as triglycerides. As always, the brain will use the new glucose entering the blood for energy and the kidneys will filter waste from the blood to be excreted as urine. Figure 10: Each of the organ’s roles during feasting in maintaining glucose homeostasis. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 87 STUDENT RESPONSES In diabetes, the messages from the pancreas do not get sent out correctly because insulin does not function. What happens in the liver, adipose and muscle of someone that is diabetic after they eat a meal? _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ ____________________________________________________________________________________________________ Remember to identify your sources _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ Wo r k b o o k Lesson 2.3 _____________________________________________________________________________________________________ ___________________________________________________________________________________________ 88 TERMS TERM DEFINITION Adipose A type of cell or tissue that is used by the body for the storage of fat. Glycemic Index A system of ranking foods based on their effect on blood glucose concentrations. Lipogenesis The metabolic formation of fat. For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 2.3 89 LESSON 2.4 WORKBOOK Part two: Glucose homeostasis in the blood – Un-Storing energy DEFINITIONS OF TERMS Fasting — A state of abstinence from all food or drinks that provide calories. For a complete list of defined terms, see the Glossary. In the previous lesson we learned about the metabolic pathways the liver uses to shuttle energy from glucose into storage as glycogen, fat, and amino acids. In this lesson, we will focus on the reverse: metabolism of glycogen, fats and amino acids to generate glucose. We will also discuss the different stages your body undergoes during fasting. Low blood sugar: Causes and consequences Why is low blood glucose a problem? Wo r k b o o k Lesson 2.4 Even with all of the built in mechanisms we have to maintain glucose homeostasis there is still a normal range in which glucose rises and falls in the blood. After we eat, the extra energy from food is stored as glycogen in the muscles and the liver, and as triglycerides in the adipose tissue. Between meals, these stores of energy are broken down, providing energy until you eat again. It is normal for blood glucose concentrations to Figure 1: The symptoms of slowly decline a bit between meals, but severe drops in glucose low blood sugar. are rare in healthy individuals. Some symptoms of low blood sugar are hunger, feeling jittery, nauseous, confused or light headed. More symptoms are shown in Figure 1. Some health conditions can lead to dangerously low levels of glucose, including diabetes and excessive alcohol intake. Because the brain relies on glucose for energy, not having adequate blood glucose levels will stress the brain. Having excessively low glucose concentrations in the blood for long periods of time can lead to seizures, fainting, coma or even death. 1. What happens to the blood glucose concentrations of a healthy individual between meals? aa. It rises slightly. bb. It drops to a dangerously low level. cc. It slowly drops, but is not dangerous. dd. It remains constant. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 90 LESSON READINGS The pancreas senses low blood glucose DEFINITIONS OF TERMS Glucagon — A hormone formed in the pancreas that promotes the breakdown of glycogen to glucose. Gluconeogenesis — A metabolic pathway that results in the generation of glucose from other carbon substrates, such as glycerol and amino acids. For a complete list of defined terms, see the Glossary. Specific hormones are released from your Low$Blood$Glucose$ Glucagon$Signals$the$Liver$ digestive system when Promotes$Glucagon$Release$ $to$Un;Store$Glucose$$ energy stores are full or are dropping. Recall from Lesson 2.3 that when Insulin$ glucose levels increase the pancreas releases insulin. Similarly, the pancreas Pancreas( Liver( will sense when the blood glucose levels are low Figure 2: Low levels of glucose stimulate the pancreas to make glucagon that signals the liver to un-store glucose. and send the message to storage organs that more glucose is needed in the blood. The pancreas sends this signal in the form of glucagon, a hormone made out of amino acids. Glucagon opposes the actions of insulin, and stimulates the production and release of glucose. Therefore, the result of glucagon being released from the pancreas is an increase in glucose concentrations in the blood. In addition to insulin and glucagon, hormones are released from other parts of your digestive system that send signals to the brain regarding the state of energy storage. This is an intricate process involving several organs and signaling systems. We will learn a lot more about these hormones, and how your body tells your brain that it is time to start and stop eating in Unit 3. The liver is the master regulator of blood glucose We learned in Lesson 2.3 that the liver is the master regulator in determining how glucose will be stored. The liver is also the organ that delivers glucose to the blood when blood glucose concentrations get too low. The liver will break down its glycogen stores and release them into the blood. Remember that the muscle cannot export its glucose, so even if the muscle has leftover glycogen to break down into the glucose, that glucose can only be used in the muscle. Wo r k b o o k Lesson 2.4 2. What is the pancreas' response when more glucose is needed in the blood? aa. It releases glucagon. bb. It releases insulin. cc. It releases glucose. dd. It releases fatty acids. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 91 LESSON READINGS The conundrum: How does the energy from fat and amino acids reach the brain? Glucose (Blood) If every organ in our body could use fat or amino acids for energy then we would not need to maintain a steady concentration of blood glucose. We know that this isn’t the case, because both the brain and the red blood cells rely on glucose as their energy source. To get around this problem, the liver can make new glucose to release into the blood from the carbon in amino acids and triglycerides, a process called gluconeogenesis (‘gluco’ = glucose, ‘neo’ = new, ‘genesis’ = generation). Gluconeogenesis Amino Acids Triglycerides Figure 3: Only the liver can make glucose from fat and protein through gluconeogenesis. Converting stored energy into glucose Because the brain normally relies on glucose for energy, there must be a constant supply of glucose into the blood stream even when other tissues are using fatty acids or amino acids as their energy source. When glycogen stores are not enough, the liver will make new glucose to export into the blood through gluconeogenesis. Figure 4: Un-storing energy: triglycerides from adipose cells and amino acids from muscle cells are the batteries. Wo r k b o o k Lesson 2.4 Counting carbons: from Acetyl CoA to glucose Gluconeogenesis makes glucose by starting with an intermediate in the citric acid cycle and undergoing several reactions to yield glucose. Another way to think of gluconeogenesis is as the reverse of glycolysis. The two carbons in acetyl CoA can be added to other intermediates in the citric acid cycle that contain four carbons, resulting in a six-carbon molecule of glucose. 3. Which of the following substrates can be used for gluconeogenesis? aa. Amino acids. bb. Glycerol. cc. Acetyl CoA. dd. All of the above. 4. How are triglycerides used as energy in the body? aa. Fatty acids are used in the citric acid cycle in every cell of the body. bb. Fatty acids are used for energy in most cells, glycerol is used for gluconeogenesis in the liver. cc. The fatty acids must first be converted to glucose. dd. Only the adipose tissue uses triglycerides for energy. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 92 LESSON READINGS Glucose is created from amino acids DEFINITIONS OF TERMS Lipolysis — The metabolic breakdown of lipids to release energy. Urea — A nitrogen-containing compound mostly made from degraded proteins. For a complete list of defined terms, see the Glossary. The intermediates in the citric acid cycle that are added to acetyl CoA to make glucose are made from amino acids. Remember that amino acids are made from the carbon chain and an amino group; the nitrogen-containing amino group of the amino acid is broken off, leaving the carbon skeleton. This results in free nitrogen, which can be harmful to our cells if left floating in the blood. The liver will package this nitrogen up as urea, which is excreted in urine. Physicians can determine if a patient is breaking down excesses amino acids because they will have high urea concentrations in their urine. Muscle Glucose Acetyl CoA Amino acids Urea Citric acid cycle Figure 5: The liver can make glucose from acetyl CoA and the carbon skeletons of amino acids, in a process called gluconeogenesis. This creates extra urea, which is excreted in the urine. The carbons of amino acids are required for the synthesis of new glucose, and amino acids used to build muscles are the first to be broken down when dietary amino acids run out. Because of this, whenever your body is in a state of needing to undergo gluconeogenesis, your muscles are most likely being broken down to provide amino acids. Energy is released from Fat Glucose Acetyl CoA Citric acid cycle Triglyceride Adipose Lipolysis Amino acids Wo r k b o o k Lesson 2.4 Figure 6: Triglycerides stored in the adipose tissue are broken down to acetyl CoA by lipolysis. Amino acids are used as intermediates in the citric acid cycle. As triglycerides are metabolized in a process called lipolysis (‘lipo’ = lipid, ‘lysis’ = to break) they produce one molecule of glycerol that can be used to make glucose, and three fatty acids that are used to generate ATP. The process of producing ATP from fatty acids was discussed in Lesson 2.2. The carbons of the fatty acids chains are broken off, two at a time, and converted into acetyl CoA. This acetyl CoA is used in the citric acid cycle to generate NADH and FADH2 for the electron transport chain. The three carbons of glycerol are then used directly in the synthesis of new glucose. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 93 LESSON READINGS The type of energy store you use depends on how long you have been fasting The body’s response to fasting is largely a function of how long one has gone without eating. For this reason we will discuss fasting in three stages: The first hours of fasting, 1-7 days of fasting, and more than a week of fasting. We can use these stages as a guideline, however each person’s metabolism and body is unique, therefore the times listed here may vary for each individual. 0-12 hours after eating 1-7 days after eating One week after eating Wo r k b o o k Lesson 2.4 Components to be broken down: Liver and muscle glycogen stores. Triglyceride stores in adipose Broken down into: Glucose Body protein Amino acids Used for: Energy for the brain, red blood cells and other cells Fatty acids and Fatty acids: energy for cells other than glycerol the brain and red blood cells; Glycerol: gluconeogenesis Body protein Amino acids Intermediates in citric acid cycle; carbons of some amino acids used for gluconeogenesis Triglyceride stores in Fatty acids and Fatty acids: energy for cells other than adipose glycerol; ketone the brain and red blood cells; Glycerol: bodies gluconeogenesis (as long as amino acids are available) Ketone bodies: energy for the brain Gluconeogenesis until there is no spare protein to break down Triglyceride stores in Fatty acids and Fatty acids and glycerol: energy for cells adipose glycerol; ketone other than the brain and red blood cells; bodies Ketone bodies: energy for the brain Figure 7: This table outlines the different source of energy throughout the stages of fasting and starvation. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 94 LESSON READINGS 0-12 Hours after eating Figure 8: In short term fasting the glycogen and proteins go first. In the first few hours after eating the body will use its shortterm energy stores, which include glucose from glycogen and stores of triglycerides. As the fast progresses, the liver will exhaust its stores of glycogen and rely on gluconeogenesis. The body will begin to breakdown lean muscle mass to free up amino acids that can be used to make new glucose for the brain and the red blood cells. At the same time gluconeogenesis is occurring, triglycerides will be released from adipose stores to provide energy to tissues other than the brain and the red blood cells. 1-7 Days after eating If a person is mostly sedentary, their glycogen stores will last about 2 days. The amount of glycogen you can store is related to how muscular you are. A more muscular person can store more glycogen, but the higher lean muscle mass also means that more glucose will be used to maintain those muscles. Therefore even a body builder can’t last a week on their glycogen! After the glycogen stores have been exhausted new glucose still needs to enter the blood stream for Figure 9: In long-term the brain and the red blood cells. The liver will begin to rely more on fasting proteins and fats are used. amino acids for gluconeogenesis. Glycerol from triglycerides can be used to make new glucose, but this can only occur as long as there is enough spare amino acids that can be used alongside the glycerol for gluconeogenesis. Unfortunately, only a limited amount of amino acids can be broken down for energy purposes because amino acids are used to build important structural elements in our cells. If we were to use all of our amino acids up for energy, we would be digesting our own tissues – which is not beneficial! Wo r k b o o k Lesson 2.4 After the expendable amino acids are used up, the body turns to our fat stores as the primary energy source. If triglycerides become the only energy source available, the brain will start to use a metabolite of lipolysis called ketone bodies. Ketone bodies will pass into the brain to be used in the citric acid cycle. One of the waste products of ketone bodies will be excreted in the urine and the breath, and smells sweet. Because of this, if someone’s body is breaking down fatty acids into ketone bodies for energy, their breath will smell sweet, a phenomenon called 'ketone breath'. The brain will start using ketone bodies for energy after only about 3 days of fasting, and the amount of ketone bodies that the brain relies on increases as the fast continues. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 95 LESSON READINGS By the end of the first week of fasting metabolism begins to slow down, and a person will start to feel extremely fatigued. By slowing down the metabolism, cells will use less energy and the lifespan is prolonged. After one week without eating At this point in fasting, the only energy source available is the triglycerides stored in adipose tissue. The amount of time a person can live without eating depends on the amount of their adipose tissue stores. Typically, the body can survive about three weeks before breaking down vital proteins in the muscles and organs to use as energy. Once this process begins, fatality is near. A quick review of today’s material Figure 10: Each of the organ’s roles during fasting. Wo r k b o o k Lesson 2.4 Using the figure to the left (Figure 10) we can locate the organ or tissue in which each metabolic process we’ve discussed today is occurring. The pancreas senses low blood glucose and secretes glucagon, which sends a message to the liver, telling it to export more glucose into the blood. The liver will export glucose from its own glycogen stores into the blood. The muscles break down glycogen into glucose to use for their own energy needs, and secrete amino acids into the blood from broken down proteins. The adipose tissue releases fatty acids and glycerol. The liver will then take up amino acids and triglycerides and secretes new glucose into the blood from gluconeogenesis. As always, the brain uses glucose, while the kidneys are busy excreting the extra urea that is being produced from the breakdown of amino acids. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 96 STUDENT RESPONSES We have now discussed the body’s response to fasting. What might the body’s reaction be if you were to stop eating carbohydrates completely, and no glucose was coming into the blood from the diet? How might this response differ from fasting? _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ Remember to identify your sources ____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ Wo r k b o o k Lesson 2.4 _____________________________________________________________________________________________________ ___________________________________________________________________________________________ 97 TERMS TERM For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 2.4 DEFINITION Fasting A state of abstinence from all food or drinks that provide calories. Glucagon A hormone formed in the pancreas that promotes the breakdown of glycogen to glucose. Gluconeogenesis A metabolic pathway that results in the generation of glucose from other carbon substrates, such as glycerol and amino acids. Lipolysis The metabolic breakdown of lipids to release energy. Urea A nitrogen-containing compound mostly made from degraded proteins. 98 LESSON 2.5 WORKBOOK Blood glucose in sleep, a 5 mile run…and after that Big Mac Using the things we have explored throughout Unit 2, in this lesson we will expand upon our knowledge of how the metabolic pathways affect specific body systems. We will focus on which organs are primarily involved in each metabolic pathway, and relate this to how the body maintains blood glucose homeostasis under three conditions: fasting, feasting and exercise. We will link the steps in metabolism that we have learned to real life experiences, and apply this knowledge to understand potential lifestyle changes. Now that we have an idea of how the body maintains glucose homeostasis, lets apply that knowledge to some real-life situations. We will use two characters, Edna and Mimi, as example of how metabolism changes depending on the food that we eat and our physical activity levels. The metabolism of Mimi We will begin by following our first character, Mimi, through a normal day. Mimi is a high school student that spends her time socializing with friends or studying. The food that she eats and the exercise she does are listed below. Wo r k b o o k Lesson 2.5 Time Activity Metablic Response Organs Involved 7:00 am After a full night’s sleep Mimi wakes up and eats a bowl of frosted wheat cereal with fat free milk for breakfast. Mimi’s glycogen stores were being used up while she slept, so the sugars from the cereal will replenish those stores. Any extra glucose will be converted to fat and stored. • The pancreas senses the glucose and releases insulin. • The liver and muscle store glucose as glycogen. • The liver converts extra glucose to triglycerides, which are stored in the adipose. • Amino acids from the milk will be used to make new proteins. 1. What is the main source of energy used while you sleep? aa. Amino acids. bb. Fatty stores. cc. Glycogen stores. dd. No energy is used while you sleep. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 99 LESSON READINGS Time Wo r k b o o k Lesson 2.5 Activity Metablic Response Organs Involved 10:00 am Mimi gets hungry so she eats a serving of flavored yogurt. Because of her high sugar breakfast, Mimi’s blood glucose levels have already peaked and are lowering, making her hungry. The fat, protein and sugar of the yogurt will mostly go into storage. • The pancreas senses the glucose and releases insulin. • Some glucose will be stored as glycogen, but most of it will get converted to triglycerides and stored in the adipose. • The fat will get stored as triglycerides. • Amino acids will be used to make new proteins. 1:00 pm Mimi eats a cheeseburger and drinks a soda for lunch. This meal is made up of carbohydrates, protein and fat, and because her glycogen stores haven’t been used up, energy from this meal is largely stored as fat. • The pancreas senses the glucose and releases insulin. • Almost all of the glucose will get converted to triglycerides and stored in the adipose. • The fat will get stored as triglycerides. • Amino acids will be used to make new proteins. 3:00 pm Mimi rides her bike around her neighborhood for 30 minutes. Glucose that is already in the blood will get used up first to release energy for exercise. Some glycogen stores may be broken down if blood glucose is not enough. • Exercise acts like insulin and brings glucose into the muscle cells to be used. • Glycogen from the liver and muscle will be broken down. 7:00 pm Dinnertime! A bean, rice, cheese and vegetable burrito is for dinner tonight. The fiber from the beans and vegetables will help slow the digestion and absorption of the carbohydrates, protein and fat in this meal. The glycogen that was broken down during Mimi’s bike ride is replenished. Extra energy goes into Mimi’s fat stores. • The pancreas senses the glucose and releases insulin. • Some glucose will be stored as glycogen, and some will get converted to triglycerides and stored in the adipose. • The fat will get stored as triglycerides. • Amino acids will be used to make new proteins. 9:00 pm Mimi eats a bowl of ice cream for dessert. Mimi hasn’t done anything to burn off her dinner, so nearly all of the energy from the ice cream is stored as fat. • The glucose is converted to triglycerides in the liver and stored in the adipose. • The fat will get stored as triglycerides in the adipose. 2. Where do muscles get glucose during exercise? aa. From their own glycogen stores. bb. From the liver's glycogen stores. cc. From gluconeogenesis. dd. All of the above. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 100 LESSON READINGS The case of exercising Edna Edna is also a high school student, and is very active! Edna is on the cross-country team and loves to run. Because Edna exercises regularly she has more muscle mass than Mimi. This means that Edna will burn more energy to maintain her weight than Mimi, and will use up her glycogen stores quicker. Muscles need glucose to make ATP to be able to contract. Once the available glucose in the blood is used up, other sources of glucose are used. Muscles will also rely on fatty acids for energy once the glucose is gone, but producing ATP from fatty acids takes much longer than from glucose, so fatty acids will only be used after the quick sources of energy (glucose and glycogen) are exhausted. Using the table below we can follow Edna through her day. To learn more about the effects of exercise on metabolism read the notes below the table that are marked with either a * or **. Wo r k b o o k Lesson 2.5 Time Activity Metablic Response Organs Involved 6:00 am Edna wakes up early and runs a mile before going to class. Glycogen stores were already being used up as Edna slept, so energy for her run comes from gluconeogenesis and breaking down amino acids and triglycerides. • The pancreas senses low glucose and releases glucagon. • Exercise causes glucose to enter muscle cells** • The liver and muscle break down glycogen into glucose. • The liver converts amino acids, lactic acid* and triglycerides to new glucose. • Triglycerides are broken down into glycerol and fatty acids and released from the adipose. 7:00 am For breakfast Edna eats a protein shake and a banana. This is a low carbohydrate meal, but Edna’s glycogen stores are getting low! Fructose from the banana will be converted to glucose in the liver and stored. Amino acids and triglycerides are used in gluconeogenesis. • The pancreas senses the glucose and releases insulin. • Glycogen stores in the liver and muscle will be filled up. • Amino acids will be used to make new proteins. 1:00 pm At lunch Edna eats the same things as Mimi: a cheeseburger and a can of soda. Because Edna burns glucose faster than Mimi, her glycogen stores are already being used by lunch. The glucose replenishes glycogen stores, and the fat will be used both for energy now and stored for later. • The pancreas senses the glucose and releases insulin. • The glucose will replenish glycogen stores and be used for energy now. • The fat will be used for energy and get stored as triglycerides. • Amino acids will be used to make new proteins. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 101 LESSON READINGS Time Activity Metablic Response Organs Involved 3:00 pm Edna skips an afternoon snack to go to her one-hour crosscountry practice. Glycogen will be broken down to glucose during practice. By the end of practice Edna’s glycogen stores are used up and her liver is creating new glucose for her muscles. Glucose is made from amino acids as well as from the lactic acid being produced in her muscles*. • Exercise acts like insulin and brings glucose into the muscle cells to be used. • Glycogen from the liver and muscle will be broken down. The fiber from the vegetables will help slow the digestion and absorption of the carbohydrates, protein and fat in this meal. The glucose from the starch in the baked potato replenishes the glycogen that was broken down during exercise. Extra energy goes into Edna’s fat stores. • The pancreas senses the glucose and releases insulin. • Most glucose will be stored as glycogen. • The fat will get stored as triglycerides. • Amino acids will be used to rebuild the proteins that were broken down during exercise. DEFINITIONS OF TERMS 7:00 pm Lactic acid — An acid containing three carbons that is formed in the muscles during strenuous exercise. For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 2.5 For dinner Edna eats a baked potato, green beans and roasted chicken breast. *Lactic acid can be used to make glucose During exercise the rate of the citric acid cycle can’t always keep up with the amount of glucose that is being supplied to the muscles. This is because the citric acid cycle requires oxygen to be delivered from the lungs via the blood. During anaerobic exercise like running or dancing you breathe heavily because not enough oxygen is being supplied to your brain and muscles. The citric acid cycle slows down and molecules from glycolysis build up, namely pyruvate. (Pyruvate is the molecule in the last step of glycolysis before acetyl CoA is made.) Pyruvate is converted into lactic acid, which causes the burning sensation you may feel in your muscles during exercise. Lactic acid can be converted back to glucose in the liver, where it is re-released into the blood. • Proteins in the muscle will break down to release amino acids. • The liver will make new glucose from amino acids, lactic acid and fat. Figure 1: During exercise glucose can be converted into lactic acid, or lactate in the muscle because of limited oxygen. This is transported to the liver where it is converted to glucose through gluconeogenesis. 3. Why do we breathe more heavily during strenuous exercise? aa. To increase oxygen for glycolysis. bb. To increase oxygen for the citric acid cycle. cc. To breathe out lactic acid. dd. All of the above. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 102 LESSON READINGS **Exercise can act like insulin The act of using your muscles can trigger a response that is similar to the effects of insulin. We previously learned that insulin tells the liver to store extra energy. Insulin also has an important role in the muscles: to bring glucose into the cells so that it can be used. During exercise, glucose from the blood can be brought into the muscle cells without the aid of insulin. This is important for people who are living with diabetes and do not have normal absorption of glucose. In this way, incorporating exercise into their daily routine can help regulate the blood glucose concentrations of someone with diabetes. Wo r k b o o k Lesson 2.5 4. Which of the two characters likely burns more calories in a day? aa. Mimi. bb. Edna. cc. They are likely the same. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 103 STUDENT RESPONSES What would the difference in glucose homeostasis be if someone were to go for a long run in the morning before they ate anything, compared to running an hour after eating lunch? _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ ____________________________________________________________________________________________________ Remember to identify your sources _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ Wo r k b o o k Lesson 2.5 _____________________________________________________________________________________________________ ___________________________________________________________________________________________ 104 TERMS TERM Lactic Acid DEFINITION An acid containing three carbons that is formed in the muscles during strenuous exercise. For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 2.5 105 Unit 3: Where are we heading? Unit 1: What’s in your food? Unit 2: How does your body use food? Unit 3: Introduction Unit 3: What is metabolic disease? Unit 4: How do I identify ‘good’ and ‘bad’ food? Unit 5: How does this knowledge apply to me? ______________________________________ In this unit we will focus on the question: What is metabolic disease? We will first define and investigate the metabolic and physiologic causes of obesity. Once we understand what obesity is, we can relate it to diseases like diabetes and atherosclerosis, which are both linked to obesity. 106 LESSON 3.1 WORKBOOK What is obesity and how does BMI relate? DEFINITIONS OF TERMS Obesity — The condition of being severely overweight due to excess fat. For a complete list of defined terms, see the Glossary. In this unit we will focus on the question: What is metabolic disease? We will first define and investigate the metabolic and physiological causes of obesity. Once we understand what obesity is, we can relate it to diseases like diabetes and atherosclerosis, which are both linked to obesity. This lesson focuses on obesity. We will discuss the obesity trends in the United States over the past thirty years and explore how obesity is measured. We will also touch upon what causes obesity from societal and cellular levels. Increasing obesity is a recent trend The rates of obesity around the world have been steadily rising and there seems to be no end to their growth. In the United States, obesity rates began to rise in the 1970s and have been steadily increasing since, although some researchers speculate that we may have reached the highest rates of obesity that we will see in the U.S. Obesity is associated with economic growth Wo r k b o o k Lesson 3.1 If we were to compare a graph of obesity in any given country to a graph of the same country’s economic growth, chances are the two graphs would look similar. Although this does not mean that economic growth causes obesity, we can speculate as to why these two measurements are linked. As citizens of a country become more prosperous, they likely have more food choices and can afford more calorically dense foods ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 107 LESSON READINGS 1. The wealthier a person is in the U.S., the more likely they are to be obese: aa. True. bb. False. like meat and dairy. Additionally, large food chains offering cheap and convenient food become more available to consumers, making calories easier to consume. Other lifestyle changes may also occur with economic growth that makes obesity more prevalent, such as occupation; as the typical jobs shift from actively working with one’s hands to sitting at a computer, a decrease in physical activity becomes normal. What other Figure 7. Overweight and obese, by age: United States, 1971–1974 through technologies 2005–2006can you think of that make eating easier, but exercising more challenging? 50 Figure 1: Fast food is a quick and inexpensive source of highcalorie food. Overweight (not including obese) 40 65 years and over Percent years It is important45–64 to note that even though obesity tends to be more 30–44 years prevalent in 30 first-world countries than third-world countries, obesity rates are growing nearly everywhere around the globe. Additionally, within many developed countries obesity is more likely to affect impover20 18–29 years ished populations than the wealthy members of society. 10 0 1971– 1974 1976– 1980 1988– 1994 50 How did all of this start? 2005– 2006 In the United States the rapid rise in obesity rates began 40 in the 1970s. Many theories 30 65 years and over have surfaced regarding what 65+ 30 45-‐64 45–64 years 20 caused the initial increases in 20 30–44 years obesity. As we learned in Unit 10 30-‐44 18–29 years 1, post World War II was a 10 18-‐29 0 time of technological innova1976– 1999– 2001– 2005– 1988– 0 1971– 1974 1980 2000 2002 2006 1994 Year tion in the food industry. The industrialized food supply that we have now is rooted in the 1940s and 1950s, when food Figure 2: Percentage of the adult population that is obese has increased from 1971 to 2006. was becoming more plentiful and processed. Some data suggests that our modern methods of food production increased caloric intake per person, leading to weight gain. Others believe that changes in activity are more to blame, although the increased incidence of obesity it likely caused by a combination of both. Obese Obesity by Age Group 50 Chartbook Health, United States, 2008 SOURCE: CDC/NCHS, National Health and Nutrition Examination Survey. 2006 2001 1996 NOTES: Overweight (not including obese) is defined as a body mass index (BMI) greater than or equal to 25 but less than 30 and obese as a BMI greater than or equal to 30. See data table for Figure 7 for estimates for children, data points graphed, standard errors, and additional notes. 1991 1986 1981 1976 1971 Percent % Obese 40 Wo r k b o o k Lesson 3.1 1999– 2001– 2000 2002 33 2. Which of the following is NOT a cause of global increases in obesity? aa. Technologies that reduce physical activity. bb. Availability of calorie-dense food. cc. Genetic mutations. dd. The industrialized food system. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 108 LESSON READINGS Why is obesity a problem? There is not an organ system in the human body that is not adversely affected by obesity. See the table (Figure 3) below for some of the diseases that are associated with obesity. Organ System Involved Digestive System Cardiovascular System Neurological System DEFINITIONS OF TERMS Skeletal System Reproductive System BMI — Body Mass Index. A measurement of relative body shape based on an individual’s weight and height. For a complete list of defined terms, see the Glossary. Disease(s) Colon cancer; Gallstones; Hepatic (liver) cancer Coronary heart disease; Stroke; Hypertension Mental health conditions like depression; Alzheimer's Disease; Dementia Osteoarthritis Infertility; Endometrial cancer; Prostrate Cancer Figure 3: Organ systems affected by obesity and the related diseases. Measuring obesity You probably have an idea of what obesity looks like, but how can we determine who is a healthy weight, overweight or obese? There are very specific criteria used to categorize people as a healthy weight, overweight and obese. Knowing this is important because when people talk about health problems linked with obesity we can know who and what are they referring to. What is a BMI? BMI Chart! BMI stands for Body Mass Index, and is based on weightper-height. To calculate your BMI use this equation: BMI = Body weight (in kg) Height2 (in m) Less,than, 18.5, • Underweight, 18.5824.99, • Healthy,Weight, 25.0829.99, • Overweight, 30.0,or,more, Wo r k b o o k Lesson 3.1 • Obese, The concept of BMI is convenient to use because the values apply to both men and women. A BMI from Figure 4: BMI can be used to classify 18 – 24.0 is considered normal, 25 – 29.9 is considered weight. overweight, and greater than 30 is obese. BMI is the measurement that is most commonly used by physicians and researchers to classify someone as healthy, overweight or obese, because at the population level weight-per-height is closely related to body fat content. There are however some limitations to using only BMI as a measurement of health for an individual. 3. A person with a BMI of 31 is classified as 'obese'. aa. True. bb. False. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 109 LESSON READINGS Problems with BMI: Population vs. the individual Figure 5: Someone with excess muscle mass may have the same BMI as someone with excess fat. BMI tables have been compiled from studies of large population groups, so when these tables are applied to a population they provide good estimates of the weight range associated with health and longevity. If you look at the BMIs of thousands of people, individuals with higher BMIs are almost always heavier due to excess fat, not muscle. However, they do not necessarily indicate the healthiest body weight for each individual. For example, athletes often have extra lean body mass and little body fat so they will weight more than average. Just using BMI to evaluate health, an athlete may be obese even though little of their body weight is from fat. Ideally, establishing a healthy weight for an individual would take into account that person’s body composition, family history of weightrelated diseases, and ethnicity. Other measurements of obesity Measuring the percentage of someone’s total weight from fat is a good way to determine if an individual is healthy. Body fat can range from 2 to 70% of ones total body weight, with the desirable levels being between 21 to 35% for women and 8 to 24% for men. In this regard, individuals with a body fat percentage above these levels are considered overweight or obese. There are multiple ways to measure body fat composition. Some commonly used methods include: ■■ Skinfold thickness — Uses calipers to measure the fat layer directly under the skin at multiple sites. (See Figure 6.) ■■ Bioelectrical impedance — Measures body fat content using a low-energy electrical current. The more fat a person has, the greater the resistance to electrical flow through the body. Wo r k b o o k Lesson 3.1 ■■ Dual energy X-ray absorptiometry (DEXA) — Measures both body fat and bone mass density using low-energy X-rays. Figure 6: A skinfold caliper can estimate fat mass. 4. BMI is: aa. A useful tool for measuring the health of a population. bb. The definitive measurement of an individual's health. cc. Calculated using height, weight, gender and age. dd. A score that can easily fluctuate from day-to-day. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 110 LESSON READINGS Where fat is located matters! DEFINITIONS OF TERMS Nature — The contribution of genetics to an individual’s health. Nurture — The contribution of lifestyle and environmental factors to an individual’s health. For a complete list of defined terms, see the Glossary. Not only how much fat, but also where the fat is stored can predict health risks. Some people store fat in the upper body areas, resulting in an apple-shaped body. Others store fat lower in the body, resulting in a pearshaped body. Excess fat in either place generally spells trouble, but upper-body obesity brings higher risks for obesity health associated diseases. For example, people that are apple-shaped are at higher risk for cardiovascular disease, hypertension and type 2 diabetes. Figure 7: People that carry weight in their mid-section are 'apple shaped', and are at higher risk for cardiovascular disease and diabetes. What causes obesity? Energy in and energy out You may have heard the law 'energy is neither created nor destroyed'. Therefore, you can think of energy balance as an equation: Energy Input = Energy Output, which can be translated as the amount of energy you consume through food must equal the amount of energy used for metabolism, digestion, physical activity and all cellular functions requiring ATP. If your energy intake from food exceeds your output, you will gain weight over time as you store excess energy as fat. To maintain your weight, you must match energy input to energy output. This may seem simple, but managing ones weight can be challenging for reasons that we will explore in the following lessons. Nature versus nurture Wo r k b o o k Lesson 3.1 Figure 8: Genetic differences in metabolism may not play as big of a role in obesity as we once thought. Both genetic and environmental factors can increase a person's risk of obesity. Experts in the field of obesity research are at odds over the relative importance of nature and nurture. Studies in pairs of identical twins give us some insight into how genetics contribute to obesity. Even when identical twins have been raised apart from one another, they tend to show similar weight gain patterns both in overall weight and in weight distribution. These studies suggest that nature (genetics) has more to do with obesity than nurture (life style habits: nutrition and exercise). 5. Which of the following is an example of how 'nurture' may contribute to obesity? aa. Being born with a 'fast' metabolism. bb. Mindless eating. cc. Leptin deficiency. dd. All of the above. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 111 LESSON READINGS Before&Lep)n& DEFINITIONS OF TERMS Mindless eating — The act of eating food without mentally thinking about it. Polymorphisms — A mutation in a gene that results in abnormal function of the protein the gene encodes. A,er&Lep)n&&&&&&& Figure 9: A patient with leptin deficiency before and after administration of leptin. There are few rare examples of single gene mutations or polymorphisms that lead to an increased risk of obesity. One example is a leptin deficiency that is associated with severe early-onset obesity. Leptin is a hormone released from the adipose tissue and that signals the brain when we are full. The brain in turn tells us to stop eating. In cases of leptin deficiency the patient will overeat because they never feel full. Simply administering leptin to these patients helps them lose weight. However, leptin deficiency only affects very few people and is not the cause of weight gain for most individuals. Conversely, leptin levels typically increase in obese people. Some researchers argue that body weight similarities between family members stem more from sharing learned behaviors than from genetic similarities. Even couples with no genetic link often behave similarly toward food and eventually assume similar degrees of leanness or fatness. These proponents of nurture propose that environmental factors such as high-fat diets and inactivity literally shape us. Perhaps the best argument to this point is that our gene pool has not changed much in the past 50 years, but the number of obese people has grown in epidemic proportion. Hence, the obesity epidemic is most likely related to nurture (life style changes), or an interaction between nurture and nature. How does our environment contribute to obesity? For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 3.1 Our everyday surroundings have a lot to do with the lifestyle choices we make. You have probably noticed that you are more likely to eat food if it is sitting next to you. Have you ever sat down to watch a movie with some popcorn, and before you realize it you’ve eaten the whole bag? This mindless eating is a documented response to not being actively engaged with the act of eating. To tackle this it’s a good idea to keep sweets and snacks outside of arms reach if you are working at a desk or watching television. There are several Figure 10: We can mindlessly eat an entire other aspects of our environment that make eating well and getting bowl of popcorn withenough physical activity challenging. In fact, some researchers out realizing it! have coined the term 'obesogenic environment' to describe this problem. If you live in a neighborhood where walking is difficult because of safety concerns or lack of sidewalks, then you may live in an obesogenic environment. Similarly, our easy access to cheap, calorie dense food instead of nutritive, healthy foods promotes the obesogenic environment. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 112 STUDENT RESPONSES If someone wanted to lose weight how could they do it? List three environmental changes they could make. Discuss changes in energy balance that would be needed for weight loss (both in energy input and energy output). _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ ____________________________________________________________________________________________________ Remember to identify your sources _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ Wo r k b o o k Lesson 3.1 _____________________________________________________________________________________________________ ___________________________________________________________________________________________ 113 TERMS TERM For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 3.1 DEFINITION BMI Body Mass Index — a measurement of relative body shape based on an individual’s weight and height. Mindless Eating The act of eating food without mentally thinking about it. Usually happens when you’re distracted by work or entertainment. Nature The contribution of genetics to an individual’s health. Nurture The contribution of lifestyle and environmental factors to an individual’s health. Obesity The condition of being severely overweight due to excess fat. Polymorphism A mutation in a gene that results in abnormal function of the protein the gene encodes. 114 LESSON 3.2 WORKBOOK What is fast and slow metabolism? In the last lesson we saw data showing that the extent of obesity in the United States has risen dramatically, and we evaluated how obesity is measured. In this lesson we will explore how exercise and body composition relate to metabolic rates. The concepts we will cover include the idea that ‘fast’ and ‘slow’ metabolism is largely a consequence of lean muscle mass. We will also explore other factors that may contribute to metabolic rate, such as efficiency of food absorption. Our metabolism determines our caloric needs In Unit 2 we learned a lot about metabolism. Metabolism is the process of breaking down macronutrients to release energy, which in turn is used by every cell in the body. How does this process of metabolism relate to how much we should eat and the idea of fast and slow metabolism? Are you stuck with the metabolism you were born with? Can you alter your metabolism? If you want to gain or lose weight, slowing or speeding up your metabolism seems like a good way to do it. Although there are some factors that you may be able to change about your metabolism, like muscle mass and your diet, others like your age, you are stuck with! Wo r k b o o k Lesson 3.2 ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 115 LESSON READINGS 1. Which of the following is NOT associated with a fast metabolism? aa. Muscle mass. bb. Younger age. cc. Hyperthyroidism. dd. Iodine deficiency. Muscle mass can influence your metabolic rate DEFINITIONS OF TERMS Thyroid — A large gland in the neck that secretes thyroid hormone. For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 3.2 A person that can eat a lot of food and never gain weight may be enviously labeled as having a 'fast metabolism', but are there biological reasons that explain this phenomenon? It is true that some people burn through calories quicker than others, but this effect is not so much based on luck, but rather based on the body composition of each individual. We have previously introduced the concept that muscle tissue is more metabolically active than fat tissue. Therefore, a person with more muscle mass will need more calories to maintain that tissue than a person that weighs the same but is made up mostly of fat tissue. In fact, just maintaining 5 pounds of lean muscle is estimated to costs about 100-250 calories per day! Figure 1: Muscles use more calories to maintain than fat. The thyroid controls metabolic rate The thyroid is a gland located in your neck that produces thyroid hormone from amino acids and iodine. One of the main roles of the thyroid is to regulate metabolism by making thyroid hormone and sending it throughout the body. Thyroid hormone passes into cells where they change the expression of genes that are involved in metabolism of carbohydrates, lipids and proteins. By changing the amount of thyroid hormone in a cell, the rate that carbohydrates, lipids and proteins are metabolized is also changed. Thyroid disorders can speed up or slow down metabolism, depending on whether the thyroid is making too much or too little thyroid hormone. People with hyperthyroidism have too much thyroid hormone, and may feel sensitive to heat, be hyperactive and generally have a faster metabolism. People with hypothyroidism do not make enough thyroid hormone and are often cold, have little appetite, are sluggish Figure 2: The thyroid is a butterfly shaped gland and have a slower metabolism. Having located in your neck. Thyroid hormone is an imporeither an under or overactive thyroid can tant regulator of metabolic rate. alter body composition because of these changes in metabolism. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 116 LESSON READINGS 2. Which of the following can reduce metabolic rate? aa. Increasing muscle mass. bb. Hyperthroidism. cc. Eating too few calories. dd. Eating too many calories. Thyroid disorders are relatively common in the U.S. (about 5-8% of the population is affected), and are more likely to affect older adults and women. If someone is diagnosed with a thyroid disorder they can receive medication to correct thyroid hormone concentrations. Because iodine is necessary for the production of thyroid hormone, iodine deficiency results in hypothyroidism. To reduce cases of hypothyroidism due to iodine deficiency, most salt in the United States is fortified with iodine. Low calorie and low carbohydrate diets slow down metabolism Figure 3: Iodine is added to salt to prevent thyroid problems. It is true that if you consume fewer calories in a day than you burn, you will eventually lose weight. Unfortunately, the simple equation of energy input equaling energy output isn’t always true. When a very low calorie diet is consumed, and not enough calories are supplied to fuel cellular processes and physical activity, metabolism actually slows down. A drop in caloric intake below 1000 calories a day can lead to a reduction in metabolic rate by 50%! The body will adapt by increasing metabolic efficiency, so each cell will use less calories to perform its normal functions. Non-essential cellular functions will cease, and a feeling of extreme fatigue will set in. Additionally, eating a calorie restricted diet may hinder the muscle’s ability to grow, so if you are eating few calories but still exercising your muscles will not be able to repair themselves and grow, leading to a further reduction in muscle mass. As we know, your muscle mass affects your metabolic rate, so a decrease in muscle mass will also reduce the 'speed' of metabolism. Wo r k b o o k Lesson 3.2 Figure 4: Cutting carbohydrates completely from the diet may reduce your muscle’s ability to grow. Similarly, a diet that is restrictive in carbohydrate intake will rely on digesting proteins from muscles for glucose. Recall that the liver performs gluconeogenesis using amino acids to make new glucose to export to the blood for the brain and red blood cells. Without carbohydrate consumption gluconeogenesis is the only source of glucose, and amino acids from the muscle and the diet will be processed into glucose. If a person is consuming a carbohydrate-free diet and still exercising regularly, amino acids may be shuttled away from the muscles and to the liver instead, reducing the person’s ability to build new muscle tissue. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 117 LESSON READINGS Some things you just can’t change DEFINITIONS OF TERMS Basal metabolic rate — The rate that the body uses energy while at rest to keep vital functions going, such as breathing and keeping warm. Energy expenditure — The total amount of energy used by a body; can by calculated by adding up basal metabolic rate, energy used for physical activity and the thermic effect of food. For a complete list of defined terms, see the Glossary. Figure 5: Resistance training, like weight lifting, can help maintain muscle mass as we age. As we age our metabolic rate tends to decrease. Children will burn through calories much faster than older adults. This is in part because organs (like the heart, liver, brain and kidneys) make up a larger proportion of a child’s body weight than an adult, and organ tissue accounts for large portion of the calories burned. Moreover, children’s bodies are growing rapidly, and calories must be used to grow their tissues and organs. Metabolism drops substantially after puberty is completed, and then slowly declines throughout the rest of life largely because of a loss of lean muscle mass. While we cannot stop ourselves from aging, we can reduce its impact by participating in resistance training, which builds muscle, and eating more protein rich foods, which helps us maintain muscle mass. There is some evidence that you may have inherited your metabolic from your parents. Studies in twins have demonstrated that people with identical genetics have similar metabolic rates, however the contribution of genetics to metabolism hasn’t been completely sorted out. It seems that your genetics may play a role in determining your metabolism, but your metabolic rate is not set in stone, and can be altered by exercise and diet. How is energy from metabolism used? We have now learned that once energy is released from food it is used for physical activity and biological processes. We will now break down energy expenditure into three categories: basal metabolic rate, thermic effect of food, and physical activity. Basal metabolic rate uses the most calories Wo r k b o o k Lesson 3.2 Basal metabolic rate represent the minimal amount of energy used in a fasting state to keep a resting, awake body alive in a warm, quiet environment. For a sedentary person, basal metabolism accounts for about 60-70% Figure 6: Energy expenditure can be divided into three categories: basal metabolic rate (60-70% of energy expenditure, physical activity (25-40%) and the thermic effect of food (5-10%). 3. Physical activity can increase energy expenditure by: aa. Burning more calories. bb. Increasing muscle mass. cc. Reducing muscle loss. dd. All of the above. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 118 LESSON READINGS of energy expenditure. Some of the processes involved include the beating of the heart, respiration of the lungs, and activity of the liver, brain and kidneys. The building up and breaking down of your muscles also uses energy that contributes to the basal metabolic rate. We can’t change the size or metabolic rate of most organs in our body, but we can increase the size (and therefore the metabolic rate) of the muscle tissue. Amount of calories used for physical activity depends on you! DEFINITIONS OF TERMS Physical activity — Movement that we consider exercise, including resistance training, sports and dancing. Physical activity increases energy expenditure above and beyond basal energy needs by as much as 25-40%. By choosing to be active or inactive we can change how much energy we expend in a day. Unfortunately, energy expenditure from physical activity varies widely among people, so it’s not possible to give a formula for how much activity is needed to increase energy expenditure by a certain number of calories. Physical activity may have the most effect on energy expenditure by changing our body composition (increasing muscle mass), in turn changing the basal metabolic rate. Thermic effect of food — Energy used to digest, absorb and metabolize the food that we eat. For a complete list of defined terms, see the Glossary. Figure 7: People that fidget burn calories through NEAT: non-exercise activity thermogenesis. Another type of energy expenditure due to exercise is called NEAT, which stands for non-exercise activity thermogenesis. NEAT is the energy that is used for everything that is not sleeping, eating or what we consider exercise. This means that walking to school or the grocery store, cooking a meal, gardening, fidgeting, and basically any movement you do that is not intended to be exercise is considered NEAT. Because NEAT encompasses most of our movement a person that does a lot of exercise but has a low NEAT level may still be at risk for becoming overweight of obese. On the flip side, people that tend to fidget more, or get their exercise by walking to work or taking stairs instead of elevators may be able to stave of weight gain over time. Energy is used to digest food Wo r k b o o k Lesson 3.2 In addition to BMR and physical activity, the body uses energy to digest, absorb and metabolize the food that we eat. This is called the thermic effect of food, and is like a sales tax. We’re charged 5-10% of the total energy that we eat to cover the cost of processing the food. For every 100 calories consumed, 5-10 of those calories are used to simply process the food. In addition, food composition influences how many calories are lost to the thermic effect. For example, a protein rich meal has a higher thermal effect than a carbohydrate or fat rich meal, because it takes more energy to metabolize amino acids than glucose or fatty acids. In addition, large meals result in a higher thermal effect of food than the same amount of food eaten over many hours. 4. Going to soccer practice would be considered _____, while using energy to sit up straight all day is considered _____. aa. Physical activity; basal metabolic rate. bb. Exercise; physical activity. cc. NEAT; basal metabolic rate. dd. Physical activity; NEAT. 5. Energy used to break nutrients free from a fibrous food is considered: aa. NEAT. bb. The thermic effect of food. cc. Basal metabolic rate. dd. All of the above. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 119 STUDENT RESPONSES Mary is a 68-year-old woman who feels her metabolism has 'slowed'. What would you tell Mary about the possible causes of this change? How can she speed up her metabolism? _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ ____________________________________________________________________________________________________ Remember to identify your sources _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ Wo r k b o o k Lesson 3.2 _____________________________________________________________________________________________________ ___________________________________________________________________________________________ 120 TERMS TERM For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 3.2 DEFINITION Basal Metabolic Rate The rate that the body uses energy while at rest to keep vital functions going, such as breathing and keeping warm. Energy Expenditure The total amount of energy used by a body; can by calculated by adding up basal metabolic rate, energy used for physical activity and the thermic effect of food. Physical Activity Movement that we consider exercise, including resistance training, sports and dancing. Thermic Effect of Food Energy used to digest, absorb and metabolize the food that we eat. Thyroid A large gland in the neck that secretes thyroid hormone. 121 LESSON 3.3 WORKBOOK How do we decide when and how much to eat? DEFINITIONS OF TERMS Appetite — The psychological desire to eat, driven by feelings of pleasure from the brain. Hunger — The biological or physiological need to eat, caused by a release of hormones from the digestive tract. For a complete list of defined terms, see the Glossary. In the last lesson we discussed what causes fast and slow metabolism, and arrived at the idea that a person’s metabolic rate does not lead to obesity, rather, restricting caloric intake to the metabolic needs of the individual is the key to avoiding obesity. Why then is it so hard to regulate weight? In this lesson we will explore the signals that regulate sensations of hunger and satiation, and will spend the next two lessons relating these signals to appetite and obesity. Hormones regulate our hunger We know that glucose homeostasis is a highly regulated process, and if you’re healthy blood glucose concentrations do not vary beyond a normal range. Yet, even when blood glucose concentrations are normal we may have the urge to eat. So if low glucose isn’t the factor telling us to eat, how does the body and mind sense hunger or satiety? There are two general driving forces that influence our desire to eat: ■■ Hunger – The primary physiological drive or need to find and eat food. ■■ Appetite – The primary psychological drive or desire to find and eat food that often occurs when there is no obvious hunger. Signals of hunger Wo r k b o o k Lesson 3.3 We have previously learned that the pancreas is tasked with the responsibility of sensing glucose concentrations in the blood and secreting hormones in response to too high, or too low glucose. Insulin is secreted when glucose levels are high, and glucagon is secreted when glucose levels are low. 1. Wanting to eat food because nutrient levels in the blood are low is an example of: aa. Hunger. bb. Appetite. cc. Addiction. dd. Satiety. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 122 LESSON READINGS As you know, these hormones can travel to other cells and organs in the body, telling them to either release stored energy or to store incoming nutrients for later use. Likewise, other organs will release hormones that will travel to the brain, signaling that we either need to stop or start eating. The important organs (other than the brain) and the hormones in the process are: DEFINITIONS OF TERMS Circadian rhythm — A 24-hour biological cycle of activity that drives hormonal releases. For a complete list of defined terms, see the Glossary. ■■ The stomach releases ghrelin in response to low nutrients in the blood – this stimulates hunger. ■■ The pancreas releases insulin in response to blood glucose levels increasing – this makes you feel full. Pancreas – Insulin! Small Intestine – CCK! Stomach – Ghrelin! Large Intestine – PYY! Adipose – Leptin! Figure 1: Hormones are released from the digestive tract that send hunger or satiety signals to the brain. ■■ The adipose tissue releases leptin when energy stores are growing – this makes you feel full. ■■ The small intestine releases cholecystokinin (CCK) when fatty acids and some amino acids enter small intestine– this makes you feel full. ■■ The large intestine releases peptide YY (PYY) in response to feeding– this makes you feel full. Hormones regulating hunger can follow your sleep cycle Wo r k b o o k Lesson 3.3 Throughout the day and night several hormones in our body are released in a cycle called the circadian rhythm. Hormones that follow the circadian rhythm are responsible for making you sleepy at night time, and alert during the day time. Things like changing time zones and being exposed to too much blue light at nighttime can disrupt our circadian rhythm. Blue light is the wavelength of light we are exposed to throughout the day. Before electricity, the only way we obtained blue light exposure Midnight Noon Midnight was by the sun’s rays. Now we are exposed to blue light coming Figure 2: Hormones affected by the circadian rhythm are from televisions, computer released in a cyclical pattern throughout the day. 2. The circadian rhythm is: aa. The natural 24-hour cycle of the body. bb. Disrupted by blue light. cc. What makes you tired after sunset. dd. All of the above. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 123 LESSON READINGS screens, cell phone screens and fluorescent light bulbs, which can all mimic daytime light in our brain. This in turn can have an effect on the release of some hormones. The release of ghrelin, insulin and leptin are all cyclical and may be influenced by the circadian rhythm. For example, people that constantly lack sleep, such as people that work the nightshift at their job, tend to have increased circulating ghrelin and decreased circulating leptin levels in their blood. This in turn leads to increased feelings of hunger, and may eventually lead to obesity. The next time you stay up all night see if you notice your hunger levels changing the following day! DEFINITIONS OF TERMS Hypothalamus — A region in the brain that coordinates homeostatic activity, controlling body temperature, thirst and hunger. Satiety — The feeling of being full, or sated. For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 3.3 Our brain interprets signals sent from the body The organs of the body are important sensors and signalers of eating because they are the “feet on the ground” that know when nutrient and energy levels are getting too high or too low. But how does the brain interpret these signals into behaviors like eating or not eating? The hypothalamus is the control center of hunger The homeostatic regulation of food intake is under the control of the hypothalamus: a tiny structure in the base of the brain that is the master regulator of most of the body’s homeostatic mechanisms. The hypothalamus receives, coordinates and responds to metabolic cues and signals from the digestive system. By integrating these signals, the hypothalamus tells us when we need to eat to maintain our body weight. It is clear however, that higher brain centers above the hypothalamus have a huge influence on what and how much food we eat. The reward pathway, for example, controls our desire to eat, and may be to blame for food cravings. As we will see, our inability to forego these rewarding aspects of food can override the long-term homeostatic control of food intake, and can contribute to obesity. Hypothalamus Figure 3: The hypothalamus in the brain is the homeostatic regulator of food intake. We have known for many years that the hypothalamus plays a central role in driving our need to eat. In animal studies, placing a tiny lesion in the hypothalamus can cause the animal to become obese or lean, depending on where the lesion is put. These experiments have allowed us to determine which areas of the hypothalamus are 'hunger' centers (telling us to eat), or 'satiety' centers (telling us to stop eating). As we will see below, the hunger and satiety centers of the brain are like a toggle, switching back and forth as the combination of signals received from the body fluctuate. 3. How does the hypothalamus regulate energy homeostasis? aa. It makes us feel hungry or sated. bb. It regulates metabolic rate. cc. It leads to glucose uptake in the muscle. dd. It causes stored energy to be broken down. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 124 LESSON READINGS The part of the hypothalamus that plays a key role in interpreting hunger and satiety signals is called the arcuate nucleus (ARC), as shown in the figure below. The ARC has two sets of neurons that control hunger in opposing ways: ■■ One set of neurons produces two molecules: neuropeptide Y (NPY) and agouti-related peptide (AgRP) that stimulate feeding and promote weight gain. DEFINITIONS OF TERMS Agouti-related Peptide (AgRP) — A peptide that is synthesized in the arcuate nucleus. Its release leads to feelings of hunger. Alpha-melanocyte-stimulating hormone (α-MSH) — A peptide that sends messages between neurons in the hypothalamus. Its release leads to feelings of fullness. Arcuate Nucleus (ARC) — A group of specialized neurons (nerve cells) in the hypothalamus. Neuropeptide Y (NPY) — A peptide that sends messages between neurons in the hypothalamus. Its release leads to feelings of hunger. For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 3.3 ■■ The other set of neurons produces a hormone called alpha-melanocyte-stimulating hormone (α-MSH) that reduces appetite and promotes weight loss. What makes us eat? When nutrients in the blood get low, ghrelin is released from the stomach, which travels to the ARC in the hypothalamus and activates the release of AgRP and NPY. These molecules then go to the hunger center in the hypothalamus and tell us that we need to eat. We then get the feeling of hunger and eat! What makes us stop eating? Figure 4: Regulation of hunger and satiety in the hypothalamus involves hormones from the body communicating with the arcuate nucleus, which leads us to eat or to stop eating. A number of factors can be sensed and trigger us to stop eating. Food entering our digestive tract, glucose concentrations rising in our blood and triglycerides being sent off to storage in the adipose tissue are all cues that it is time to stop eating. When these things happen, leptin, insulin, CCK and PYY are all released from their respective tissues, and all travel to the ARC in the hypothalamus. This is where things start to get tricky! The presence of leptin, insulin, CCK and PYY in the ARC stimulates the production of α-MSH, which signals the satiety center and tells us to stop eating. Additionally, leptin, insulin, CCK and PYY in the ARC will inhibit the functions of ghrelin, thereby making us feel full in two ways: one, by stimulating the satiety center, and two, by inhibiting the hunger center. Some foods may make us feel fuller than others. Because CCK is only released in response to fat and some amino acids entering the small intestine, a high carbohydrate meal may not sufficiently trigger CCK secretion, and may not give us feelings of satiation. Also, recall that foods with a high glycemic index - like highly processed, sweet foods - cause blood glucose to peak and fall quickly. This produces a fast storage of energy followed by a drop in blood glucose that will lead to a fall in insulin and leptin, which allows ghrelin to stimulate hunger. 4. Eating a meal would stimulate the release of all of the following except: aa. Leptin. bb. Insulin. cc. Ghrelin. dd. CCK. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 125 LESSON READINGS Stimulants of appetite When do you feel the urge to eat? Is it only when your body truly needs nutrients and energy? Probably not! We all get the urge to eat for a multitude of reasons, like boredom, or passing by our favorite ice cream shop. So if ghrelin isn’t stimulating this need to eat, what is? How are our senses linked to appetite? Figure 5: Simply thinking of food may make us feel hungry! We can be driven to eat simply by seeing or smelling food. This is because food activates the brain's reward center, which we will learn about in greater detail in the next lesson. By activating the reward center, we feel good after eating. Simply seeing or smelling a favorite food can activate the reward center and make us want to eat. There are some foods that give us more pleasure than others, and some people are more sensitive to getting pleasure from food than others. In general, people who experience more pleasure from eating certain foods tend to eat more, leading some researchers to believe that the brain’s reward center may play a central role in the development of obesity. On the other side of the equation, being hungry can actually increase our sense of smell. The release of ghrelin from the stomach can travel to cells that are responsible for smell and make them more sensitive. This is why the smell of food cooking is especially mouthwatering when you are hungry! Marketing food to our senses We live in a food-rich environment, and are constantly exposed to advertisements for food products. Food marketers can use our senses to sell us food even when we are not hungry. Some studies have shown that seeing a picture of a tantalizing food (like the pizza to the right) can activate the brain's reward pathways and make us want to eat. Using this knowledge, we can be driven to purchase a food simply by seeing a picture of it. Wo r k b o o k Lesson 3.3 Figure 6: Seeing images of our favorite foods can make us feel hungry even when we don't need nutrients. 5. Wanting to eat food because you smell it (not because your body needs it) is an example of: aa. Hunger. bb. Appetite. cc. Addiction. dd. Satiety. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 126 STUDENT RESPONSES How can we use the knowledge of hypothalamus and hunger and satiety signals to formulate a drug for weight loss? What process or processes would you activate or inhibit and what would you predict the outcome and side effects to be? _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ ____________________________________________________________________________________________________ Remember to identify your sources _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ Wo r k b o o k Lesson 3.3 _____________________________________________________________________________________________________ ___________________________________________________________________________________________ 127 TERMS TERM For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 3.3 DEFINITION Agouti-related Peptide (AgRP) A peptide that is synthesized in the arcuate nucleus. Its release leads to feelings of hunger. Alpha-melanocyte-stimu lating hormone (α-MSH) A peptide that sends messages between neurons in the hypothalamus. Its release leads to feelings of fullness. Appetite The psychological desire to eat, driven by feelings of pleasure from the brain. Arcuate Nucleus (ARC) A group of specialized neurons (nerve cells) in the hypothalamus. Circadian Rhythm A 24-hour biological cycle of activity that drives hormonal releases. Hunger The biological or physiological need to eat, caused by a release of hormones from the digestive tract. Hypothalamus A region in the brain that coordinates homeostatic activity, controlling body temperature, thirst and hunger. Neuropeptide Y (NPY) A peptide that sends messages between neurons in the hypothalamus. Its release leads to feelings of hunger. Satiety The feeling of being full, or sated. 128 LESSON 3.4 WORKBOOK Can you become addicted to food? DEFINITIONS OF TERMS Dopamine — A compound that sends signals from one neuron to another, and is made from the amino acid tyrosine. Dopamine reward pathway — A circuit in the brain that when activated leads to feelings of pleasure. Rewarding experiences such as food and sex stimulate the dopamine reward pathway. Nucleus accumbens (NAc) — A region of the brain that is involved in reward, pleasure, addiction, fear and laughter. Prefrontal cortex (PFC) — The anterior part of the brain (located below the forehead) that plays a role in personality, decision-making and social behavior. Ventral tegmental area (VTA) — A group of neurons that is the start of the dopamine reward pathway. Dopamine is released from the VTA to the NAc and PFC. For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 3.4 In this lesson we will examine yet another complicating factor that can thwart our intentions to maintain a healthy weight – the similarities between how our brain behaves when confronted with food and how it behaves when confronted with drugs of abuse. The realization that there are many commonalities between the addicted brain and the obese brain is a recent one, and it has significant implications for future treatments of obesity. The dopamine reward pathway The various feeding and satiety messages we learned about in the previous lesson do not single-handedly determine what and when we eat. Almost everyone has inhaled a mouth-watering dessert even on a full stomach; we often eat because food is in front of us. It smells good, tastes good, and looks good! We might eat because it is the right time of day, we are celebrating, or we are trying to overcome sadness. After a meal, pleasant memories reinforce our appetite, giving us the desire to eat. The dopamine reward pathway is responsible for our feelings of pleasure Our desire to eat is controlled by the dopamine reward pathway, which originates in an area of the brain called the ventral tegmental area (VTA). The dopamine neurons in the VTA send connections to the nucleus accumbens (NAc) and the prefrontal cortex (PFC). Don’t worry if you don’t get these terms right away, we’ll be discussing the reward pathway for the rest of this lesson. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 129 LESSON READINGS Dopamine Reward Pathway Pleasurable s1muli PFC NAc VTA The connections between the VTA, NAc and PFC are collectively called the reward pathway because they are activated during pleasurable experiences, such as eating, during sex, consuming drugs of abuse or when given praise. Because the same reward center in the brain is responsible for positive feelings after using drugs and after eating, overeating may in fact impact the brain like abusing a drug. Eating is associated with dopamine release in the reward pathway, and the amount of dopamine Figure 1: The dopamine reward pathway released during a meal can be used to predict is made up of the prefrontal cortex (PFC), how pleasurable the experience of eating was. As nucleus accumbens (NAc) and the ventral tegmental area (VTA). expected, different foods produce different levels of dopamine release, leading to different levels of pleasure from a meal. Typically, food that is high in sugars and fats are deemed more pleasurable, though this varies between people. Also as expected, the amount of dopamine released in the nucleus accumbens is reduced as a meal continues, meaning that the first bite of a food will be the most pleasurable, and all following bites will get more and more boring! Food cravings are related to the dopamine reward pathway Dopamine regulates food consumption not only because it acts on the reward pathway while eating, but also because we can be conditioned to stimuli that then drive our motivation to consume food. For example, whenever you sit down to watch a movie you may feel the urge to eat popcorn. One of the first descriptions of a conditioned response was by a scientist named Ivan Pavlov, who showed that after dogs were exposed to repeated pairings of a tone with a piece of meat, the tone itself would cause the dogs to salivate even when no food was present. It has since been discovered that this conditioning increased dopamine release in the reward pathway upon associations with food. Wo r k b o o k Lesson 3.4 Figure 2: Pavlov conditioned dogs to expect food every time a bell was rang. This increase in dopamine in the reward pathway is the cause of the intense food cravings we all experience. Like Pavlov's dogs, humans can be conditioned to associate eating with stimuli that have previously been tied to food. For some people, it is the “need” to drink coffee every morning, for others it is the “need” to finish the day with a sweet dessert. Sometimes we can pinpoint the root cause of the craving, but other times we don’t know what sets these cravings off. 1. Which best describes the dopamine reward cycle? aa. A circuit between organs of the body and regions of the brain. bb. A series of chemical reactions that release energy. cc. Regions of the brain that are connected by neurons. dd. Neurons in the hypothalamus that release signaling proteins. 2. Pleasurable stimuli: aa. Activate the dopamine reward pathway. bb. Can become addictive. cc. Lead to dopamine release. dd. All of the above. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 130 LESSON READINGS Stress triggers overeating DEFINITIONS OF TERMS Adrenal glands — Glands that sit on top of the kidneys that produce hormones that help control heart rate, blood pressure, and stress reactions. Cortisol — A steroid hormone that is released in response to stress, and increases blood glucose, suppresses the immune system and speeds up metabolism. For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 3.4 Stress can play a particularly critical role in overeating. Moderate stress will stimulate appetite and lead to overeating in a variety of mammals, from rodents to humans. This suggests that there is some stressevoked biochemical signal that modifies the reward pathway to trigger overeating. In the short-term, stress hormones released from the brain actually suppress the appetite. If stress persists, glands sitting on top of the kidneys, called adrenal glands, will release a stress hormone called cortisol. Cortisol is the stress hormone that is responsible for increasing appetite, though the reason why is not yet completely understood. Figure 3: Eating high calorie, sweet and fatty foods is a common response to chronic stress. Stress can also affect food preferences, making you want to eat food that is high in fat and sugar. These foods in turn will activate the dopamine reward pathway, giving us a sense of pleasure, and perhaps combatting our stress for a short period of time. Some research has suggested that men and women deal with stress differently. For example, women are more likely to turn to food when they are stressed, and men are more likely to consume alcohol or smoke. Can you inherit an addiction? People suffering from addiction or from obesity are often stigmatized as having little will power. Yet addiction and obesity are complicated diseases that result in structural changes in the brain that are difficult to remedy. A portion of the vulnerability to addiction may be attributed to genetic differences. For example, addictive behaviors tend to run in families, yet the contribution Figure 4: Nature vs. nurture: are of genetics and environmental factors is complex and some people more likely to be addicted to drugs or food. an area of active research. Just as the genetic and environmental influences in addiction vary between cultures and people, so does the interaction between genetics and environmental conditions leading to obesity. Understanding the relationship between innate (nature) drive for food and learned (nurture) associations that lead to obesity is an area of intense research. But one thing is clear, being addicted to substances or foods leads to dramatic changes in the structures of the brain that perpetuate the cycle of addiction. 3. Long term stress results in: aa. Suppression of the appetite. bb. Release of dopamine. cc. Feelings of pleasure. dd. Release of cortisol. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 131 LESSON READINGS This is your brain on obesity Why does the brain 'promote' obesity? Our reward pathways are particularly sensitive to high-calorie foods containing sugar and fat. This makes sense evolutionarily, because as hunters and gatherers we often failed to find food, and sometimes had to wait several days between meals. So craving calorie rich foods offered a survival advantage; it was in our best interest to seek high calorie foods, so our bodies adapted a mechanism that would find high calorie foods rewarding, motivating us to eat them. DEFINITIONS OF TERMS Inverse — Opposite in direction or effect. For a complete list of defined terms, see the Glossary. For a greater part of human evolution, sweet taste was associated with only fruits. Now that we live in a time when sugars and fats are abundant, the dopamine reward pathway can backfire. Instead of being there to protect us from starvation, our preference for high calorie foods can harm us by leading to weight gain and obesity. Figure 5: In addition to protecting us from starvation our food drive can promote obesity when an abundance of calories are available. Changes in the dopamine reward pathway Eating, smelling and seeing images of foods can lead to increased dopamine release in the reward pathway in the brain. Some research suggests that the magnitude of the dopamine response is associated with an individual’s body mass index (BMI). In general, lean individuals have an increased dopamine response when stimulated with food relative to overweight or obese individuals. This indicates that obese people may develop a tolerance to the activation of the reward pathway in response to consuming food. Wo r k b o o k Lesson 3.4 Figure 6: Dopamine is a simple molecule, that when released gives us feelings of pleasure. This blunting of the reward pathway in obese individuals may be due to a reduction in dopamine receptors present on the neurons that make up the reward pathway. In one study, the number of dopamine receptors in the reward pathway was inversely related to BMI in an obese population. The idea being that over time overconsumption of food causes a decrease in sensitivity of the reward pathway, which sets up a vicious cycle of needing excess food to feel satisfied. 4. We have evolved to prefer lowcalorie, micronutrient-light foods. aa. True. bb. False. 5. A reduction in dopamine receptors in the dopamine reward pathway would: aa. Numb the feelings of pleasure from food. bb. Heighten the sense of pleasure from food. cc. Increase sensitivity of the reward pathway. dd. Lead to severe weight loss. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 132 STUDENT RESPONSES Some scientists have attempted to make an anti-obesity prescription drug by targeting the reward pathway. What sort of side effects would you expect the drugs to produce if they are successful in inhibiting the reward pathway? Would these drugs work for reducing obesity? Why or why not? _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ Remember to identify your sources ____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ Wo r k b o o k Lesson 3.4 _____________________________________________________________________________________________________ ___________________________________________________________________________________________ 133 TERMS TERM For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 3.4 DEFINITION Adrenal Glands Glands that sit on top of the kidneys that produce hormones that help control heart rate, blood pressure, and stress reactions. Cortisol A steroid hormone that is released in response to stress, and increases blood glucose, suppresses the immune system and speeds up metabolism. Dopamine A compound that sends signals from one neuron to another, and is made from the amino acid tyrosine. Dopamine Reward Pathway A circuit in the brain that when activated leads to feelings of pleasure. Rewarding experiences such as food and sex stimulate the dopamine reward pathway. Inverse Opposite in direction or effect. Nucleus Accumbens (NAc) A region of the brain that is involved in reward, pleasure, addiction, fear and laughter. Prefrontal Cortex (PFC) The anterior part of the brain (located below the forehead) that plays a role in personality, decision-making and social behavior. Ventral Tegmental Area (VTA) A group of neurons that is the start of the dopamine reward pathway. Dopamine is released from the VTA to the NAc and PFC. 134 LESSON 3.5 WORKBOOK Homeostasis gone awry: How does the satiety pathway relate to obesity? In the last lesson we explored how the body regulates the sensations of hunger and satisfaction. In this lesson we will work our way through a primary research paper that shows how changing diet and lifestyle impacts homeostatic signals. This data has important implications for people attempting to lose weight. Our goal will be to use research and data to evaluate health claims and advertisements, allowing us to make more informed choices. Weight loss relapse: why is losing weight so difficult? With great effort and constant attention, someone can successfully lose weight and maintain weight loss. Unfortunately, people who lose weight often eventually regain that weight. It is very hard to lose weight and keep that weight off, but why? Mixed communications from adipose to the brain Wo r k b o o k Lesson 3.5 When a person gains weight, extra energy is being stored as fat in the adipose tissue. As the size of the adipose cells grow, the amount of leptin that is produced increases in tandem. Remember that leptin is the hormone that is produced in the adipose and sent to the brain to signal feelings of satiety. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 135 LESSON READINGS Normally, increased leptin signals to the brain that energy stores are full and no more food is needed, thereby maintaining homeostasis and preventing excessive weight gain. However, there seems to be a point in weight gain when these signals fail, and the brain is no longer able to 'see' the messages from leptin. This is called leptin resistance, and is very common in obese individuals. Leptin resistance is also correlated with another type of resistance that we will learn about in the following lesson: insulin resistance. With leptin resistance there is increased leptin in the blood, but the normal response in the brain (release of α-MSH and stimulation of the satiety center) malfunctions. The result is a loss of feeling full, and increased hunger despite consuming excess nutrients. Decreased Food Intake Lep7n Increased Body Weight Figure 1: Increased adipose stores increase circulating leptin, which should result in decreased hunger. This can be disrupted in obese individuals. Resetting homeostasis In general, our bodies are reluctant to change and want to maintain homeostasis. For example, if you eat a huge meal at lunchtime, you probably won’t have much appetite for dinner. Over the long term however, weight gained slowly over months and years will eventually reset homeostasis so that the body’s new 'normal' is a higher weight. It is this resetting that makes losing weight, and maintaining weight loss difficult. From an evolutionary standpoint, it was desirable to keep extra energy in our adipose stores because we were likely to live through a time of food shortage. Therefore, our bodies are programmed to hold extra calories, and are reluctant to shed fat. Wo r k b o o k Lesson 3.5 Figure 2: Our body wants to maintain the balancing act of homeostasis, and is reluctant to change. The increased circulating leptin associated with obesity is reduced back to normal levels after weight loss. While at first glance this seems like it is beneficial, the drop in leptin triggers metabolic changes in the thyroid gland that may prevent further weight loss. Recall that the thyroid is responsible for determining your metabolic rate. So, when restricting calories, the thyroid responds to the drop in leptin levels by balancing the person's current state of starvation! The thyroid then goes into starvation mode, and lowers the basal metabolic rate in an effort to save energy in the body and promote weight re-gain. 1. What is the result of leptin resistance? aa. Decreased hunger. bb. Increased satiety. cc. Increased hunger. dd. All of the above. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 136 LESSON READINGS As discussed in the last lesson, the other central hormone that regulates food intake is ghrelin, which makes us feel hungry. If you were to compare the levels of ghrelin circulating in a lean person to those in someone that has lose substantial weight, what would you expect to find? Similar to the case of the thyroid gland reducing basal metabolic rate, ghrelin concentrations increase after weight loss because the body 'thinks' it is starving, and tries to hold on to energy and re-gain energy stores. The body sends signals to the brain that energy storage reserves are emptying and need to be refilled, causing increased hunger and food consumption. How long would you expect it to take before the body reaches a new homeostatic set point: days, weeks, months or even years? DEFINITIONS OF TERMS Ghrelin — A hormone produced in the stomach that stimulates hunger. For a complete list of defined terms, see the Glossary. Understanding research data A quick glance through a newspaper or health magazine will reveal many headlines about nutrition and exercise. Journalists use results from scientific studies to make claims about what diets and foods are good or bad. These articles often confuse readers by misinterpreting or overstating claims. For instance, one week running may be good for you; the next week running may be the cause of an early death! So was the research wrong, and how can you make informed choices when messages flipflop? The only way to effectively evaluate these claims is to know how the researchers did the experiments. Figure 3: Nutrition research often makes news headlines. Knowing how the research is conducted helps us sort through the misleading reports. Using the QMDC method Reading a scientific paper is at first daunting, but it is a skill that grows with practice and is critical for understanding health claims. All primary science papers have a similar structure that we can use to navigate through the complex web of ideas. We can simplify the structure of a scientific paper into four parts, its QMDC: Wo r k b o o k Lesson 3.5 Figure 4: Asking what the BIG question is before reading through a scientific paper will make the other parts easier to understand. Q uestion: What is the main question of the paper? M ethod: How do the authors investigate this question? D ata: The data is represented in figures, and each figure has its own QMDC. C onclusion: What conclusions can you make based on the data? 2. Losing weight results in: aa. A slowing of metabolism. bb. Reduced concentration of circulating leptin. cc. Increased ghrelin. dd. All of the above. 3. Leptin is associated with ____, and ghrelin is associated with ____. aa. Hunger; satiety. bb. Satiety; hunger. cc. Fullness; satiety. dd. Pleasure; hunger. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 137 LESSON READINGS Each paper has a primary, BIG Question that is usually reflected in the overall title of the paper. Then each figure in the paper asks a more fine-tuned Question that relates to an aspect of the big question. Each figure also uses a specific Method to address the big question. The Data from the figures allow us to draw Conclusions about whether the more limited questions have been addressed, which again relates to the BIG Question. Understanding methods is key We will learn more about the different types of scientific studies in Unit 4. For now it is important to know that the type of study the researchers conducted can greatly impact the conclusions we can make. When determining the methods used in a study, ask yourself three questions: (1) What were the methods used? (2) How many measurements were made, and was the length of the study appropriate? (3) What did the researchers measure? Essentially, the more alternative explanations you can come up with to explain the results, the farther you are from making a solid health claim! Consider a study that asks the question of whether weight loss affects the risk of cardiovascular disease. Does the method of weight loss matter? Did the participants cut their calories, exercise more, or did they undergo a weight-loss surgery? Each method may give us a different answer to our BIG question. We would also need to consider how often measurements were made. Can a weight loss study be completed in a month? Probably not, because cardiovascular disease takes years to develop! To really understand the impact weight loss has on risk for cardiovascular disease, measurements would need to be taken for a long period of time. Figure 5: Determining what methods scientists used in a study allows us to make proper conclusions. Finally, how was the weight loss measured? Did the researchers simply measure the number of pounds lost, or did they measure changes in body composition? For example, if the participants in the study were exercising they may even gain weight but reduce their body fat. As you read through a scientific paper try to focus on what results the methods can give you. You may find that researchers do not always use ideal methods, but rather those that are possible. Wo r k b o o k Lesson 3.5 4. Understanding the methods used in scientific research helps you interpret: aa. The BIG question. bb. How the study was conducted. cc. What conclusions are reasonable. dd. Both B & C. ee. All of the above. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 138 STUDENT RESPONSES We have discussed the evolutionary benefits of our bodies' drive to store extra energy, and how this makes it difficult to lose weight. Even so, relative to human history obesity is a recent health problem. Given this information, would you argue that obesity is caused by genetics, by our environment, or a mixture of the two? Explain your reasoning. _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ Remember to identify your sources ____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ Wo r k b o o k Lesson 3.5 _____________________________________________________________________________________________________ ___________________________________________________________________________________________ 139 TERMS TERM Ghrelin DEFINITION A hormone produced in the stomach that stimulates hunger. For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 3.5 140 LESSON 3.6 WORKBOOK Obesity and Metabolic diseases: Diabetes and Heart disease DEFINITIONS OF TERMS Diabetes mellitus — The most common form of diabetes. Caused by a deficiency in the action of insulin. Results in high blood glucose concentrations and urinary glucose excretion. Throughout Unit 3 we have explored how the brain regulates eating. We have also seen that hunger signals may not adapt after weight loss, perhaps contributing to the weight regain that often occurs when people have lost weight by dieting. Here we further explore the consequences of obesity by focusing on diabetes and heart disease. For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 3.6 Type 2 Diabetes Figure 1: People with type 1 diabetes inject insulin to replace what the pancreas fails to make. You may already know that there are two types of diabetes mellitus: type 1 and type 2. Type 1 diabetes is believed to be genetic, is not associated with obesity, and results from dysfunction of the pancreas, which fails to make insulin. While the exact cause is unknown, it is thought that the body’s immune system attacks the pancreas, damaging the insulin-producing cells. People that are diagnosed with type 1 diabetes must take insulin when they eat food since their body cannot create its own. Because insulin is a protein, it must be administered through an injection. Taking the protein orally would not work because it would simply be digested in the stomach by peptidases. The onset of type 1 diabetes is normally in children, hence type 1 diabetes is often called juvenile diabetes. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 141 LESSON READINGS Type 2 diabetes is different, in that it develops over time and is highly correlated with obesity. With the current rise in obesity in the United States, the number of people diagnosed with type 2 diabetes has also grown, and we will focus on its mechanisms and consequences here. The onset of type 2 diabetes has been historically in people between 30 and 50 years old, so it has been called adult onset diabetes. However, the increase in childhood obesity in recent years has led to a rise in type 2 diabetes in young people, so the terms juvenile and adult diabetes are easy to misunderstand. Insulin' Insulin' Receptor' Figure 2: Insulin binds to the insulin receptor, leading to uptake and storage of blood glucose. Cause of type 2 diabetes Type 2 diabetes is highly correlated with obesity, but how obesity relates to the onset of diabetes is poorly understood. In healthy individuals, insulin is released from the pancreas and binds to insulin receptors located on cells in the liver, muscles and other organs. When insulin binds to insulin receptors, a series of enzymatic reactions and processes take place, leading to the downstream actions of insulin, such as bringing glucose into the muscles or telling the liver to package glucose and fatty acids for storage. Initially, an individual with type 2 diabetes will release insulin from the pancreas in response to high glucose as usual, but the receptors in the liver, muscles and other tissues fail to respond normally. This results in a high blood glucose concentration, as well as high blood insulin. Insulin resistance is the term used to describe this lack of normal response to insulin. The pancreas will then continue to make more and more insulin to overcome the insulin resistance, until it eventually burns out and insulin production ceases. This is one reason that unmanaged type 2 diabetes often progresses from insulin resistance to both insulin resistance and poor insulin production, requiring insulin injections. Wo r k b o o k Lesson 3.6 Researchers are still actively trying to understand how weight gain connects to insulin resistance. Although there is some evidence that inflammation may damage the insulin receptors, there is a lot remaining to be discovered! Figure 3: Years of high blood glucose in diabetics can lead to un-healing ulcers. If left untreated, amputation may be needed. 1. Which of the following would you NOT expect to occur with insulin resistance? aa. Increased blood glucose. bb. Increased blood insulin. cc. Increased storage of glucose as glycogen. dd. Increased gluconeogenesis. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 142 LESSON READINGS Long-term consequences of living with diabetes DEFINITIONS OF TERMS Diabetes is a major risk factor for heart disease and stroke, and is the leading cause of kidney failure and blindness in adults. The reason for these impairments varies by tissue, but the common cause is that extra glucose left in the blood binds to proteins, disrupting their functions. If unregulated, high blood glucose can lead to malfunctions in wound healing, resulting to ulcers (especially in the foot). If these ulcers are not cared for properly, amputation may ensue. Because type 2 diabetes is so common now and can negatively impact the body in many ways, diabetes has become the seventh leading cause of death in the United States. Treatment involves lifestyle changes Atherosclerosis — A disease of the arteries characterized by deposits of fat. Cardiovascular — Describes something that involves the heart or the blood vessels (arteries and veins). Heart disease — A structural or functional abnormality of the heart or blood vessels. Vascular — Describes something that involves the arteries and veins. For a complete list of defined terms, see the Glossary. Weight loss is the most effective treatment of type 2 diabetes. In fact if diagnosed early, type 2 diabetes can usually be completely reversed through weight loss. People living with type 2 diabetes must also monitor their blood glucose levels to ensure that they don’t get too high. Although some medications can increase insulin sensitivity, these medications alone cannot completely cure type 2 diabetes. Although type 2 diabetes starts as insulin resistance, if not managed, it may progress to the point that the pancreas becomes dysfunctional. In this case, just like people living with type 1 diabetes, so called 'brittle' type 2 diabetics must track their blood glucose concentrations and administer their own insulin. Figure 4: Using a glucose monitor, diabetics can track their blood glucose concentrations. Eating a healthy diet and exercising are the best interventions for someone diagnosed with type 2 diabetes. Remember that exercise acts like insulin, and brings glucose into the muscles cells even when insulin is not present. Because of this exercise is an effective way to lower blood glucose concentrations even in individuals with insulin resistance. Eating a diet with a low glycemic index may also help to keep blood glucose concentrations within the healthy range. Heart disease and atherosclerosis Wo r k b o o k Lesson 3.6 Heart disease, also called cardiovascular disease, is a term that refers to several conditions that affect the heart and vascular system. We will focus on atherosclerosis because it is the most common type of heart disease. Other types of heart disease include congestive heart failure and heart attack. Together, heart disease is the leading cause of death for both men and women in the United States. 2. Which of the following is a recommended treatment for type 2 diabetes? aa. Increase carbohydrate consumption. bb. Increase physical activity. cc. Eat foods with a high glycemic index. dd. Take cholesterol-lowering drugs. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 143 LESSON READINGS Development of atherosclerosis Atherosclerosis is a disease of fatty plaques building up in the vascular system. This is like a clog in a pipe that prohibits the normal flow of water. These plaques are made up of fat, cholesterol, and immune cells. While heart disease primarily affects older adults, the formation of atherosclerotic plaques begins in childhood. An atherosclerotic plaque develops in 4 steps: 1. Fat traveling in the blood within LDL vesicles become altered by inflammatory proteins, causing the recruitment of immune cells. DEFINITIONS OF TERMS Blood clot — A mass of coagulated blood. Fatty streak — The first visibly obvious step in the development of atherosclerosis. Fatty streaks are made up of immune cells and lipoproteins (LDL). Plaque — A region of fatty deposit on an artery wall that has been encapsulated by cells lining the arteries. 2. The immune cells engulf the LDL, and stick to the side of an artery. This is called a fatty streak; nearly everyone has fatty streaks in their arteries by their twenties! If you are otherwise healthy, the atherosclerosis will not progress beyond this stage. 3. If a cap of cells grows around the fatty streak, it becomes a plaque. Plaques are relatively stable, but can cause problems because they reduce blood flow. Figure 5: The stages in atherosclerosis development. 4. If a plaque becomes too big, or if the cap of cells is too thin, the plaque can rupture. This causes a blood clot to form. The clot can stay locally, impeding blood flow, or can dislodge from the artery wall and block blood flow in another location. If the clot travels to an artery in the heart it can cause heart failure. If the clot travels to the brain it can cause a stroke. Like insulin resistance, inflammation plays a pivotal role in the development of atherosclerosis. If someone has high LDL cholesterol in their blood as well as an abundance of inflammatory proteins, the beginning stages of atherosclerosis are likely to occur. This is why people at risk for heart disease are often recommended to take a low daily dose of aspirin, which is an anti-inflammatory drug. For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 3.6 Forma4on of Fa#y Plaque Blood Clot Streak Rupture of Plaque Figure 6: Atherosclerosis can cause a heart attack if blood flow is blocked in an artery in the heart. Living with heart disease There is no treatment for heart disease. Instead, a person with heart disease should adhere to a healthy diet and exercise regularly in the hope of preventing plaque rupture. 3. Atherosclerosis can result in: aa. Fatty streaks. bb. Heart attack. cc. Stroke. dd. All of the above. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 144 LESSON READINGS If the plaque does rupture this may result in a heart attack (also called a myocardial infarction), which can be lethal. People that are more likely to have heart disease are those that are overweight, smoke, have high blood pressure or high LDL cholesterol levels, and those under chronic stress. There are some medications available to lower blood pressure and cholesterol levels, which may be able to lower heart attack risk. Heart disease is sometimes called the “silent killer” because there are often no symptoms associated with heart disease until a heart attack occurs. DEFINITIONS OF TERMS How does obesity contribute to these diseases? Obesity is a risk factor for several disorders and diseases, including the two we talked about in this lesson. Others include some types of cancer, sleep apnea, osteoarthritis, infertility and gallstones. Gallstones — Crystals of bile acids that form in the gallbladder that can cause sever pain and blockage of the bile duct. Macrophage — A large cell that is involved in the body’s immune response. Osteoarthritis — A loss of cartilage in the joints that results in pain and stiffness. Sleep apnea — A temporary stopping of breathing that occurs during sleep. For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 3.6 What is it about obesity that contributes to the malfunction of so many body systems? In recent years, researchers have discovered one key aspect of obesity is that it seems to cause chronic low-level inflammation. You’ve probably experienced inflammation as the red color, swelling and heat that occur around a scrape or cut. Inflammation is also what causes the fever, aches and pains during the flu. On the molecular level, inflammation is the release of key inflammatory proteins by immune cells. When we get injured, immune cells will travel to the site of injury and release these proteins, which will expedite the healing process and kill off pathogens. Obesity is associated with chronic low-levels of inflammatory proteins circulating in the blood, but why are they there and what are they doing? Does obesity cause inflammation? Not all adipose tissue is created equal and this may relate to how adipocytes store fat. For adipose tissue to accommodate the excess storage of triglycerides seen in obesity, it can either make more cells or increase the size of the existing cells. In the latter scenario, the cells can actually grow too large and essentially burst, causing immune cells to enter the adipose tissue and clean up the mess. An important immune cell that surrounds these broken adipose cells is the macrophage. Macrophages are found in the adipose tissue of both lean and obese individuals, however the type of macrophage is different. In lean individuals, the macrophages are generally Lean-Adipose- Obese-Adipose- An#$Inflammatory-MacrophageInflammatory-MacrophageFigure 7: Adipose tissue in lean individuals generally has anti-inflammatory macrophages, while obese individuals usually have inflammatory macrophages. 4. Which of the following is a symptom of heart disease? aa. There are no symptoms until heart attack or stroke. bb. Headaches. cc. Excessive thirst. dd. Fatigue. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 145 LESSON READINGS anti-inflammatory. During obesity, the type of macrophages tends to be inflammatory, thereby increasing inflammatory factors that travel thoughout the body. This inflammation may be to blame for destruction of insulin receptors which causes insulin resistance, and may also be the cause of leptin resistance, which we discussed in the previous lesson. Chronic low-level inflammation may also be the reason why some obese people are more likely to develop certain types of cancer, including colorectal cancer and breast cancer. Stay tuned because future research in this area is promising and may lead to better treatments and preventative measures for obesity-associated diseases. Can people who are obese be healthy? Figure 8: Some obese people are just as metabolically fit as lean people, possibly because they do not develop chronic inflammation. Wo r k b o o k Lesson 3.6 Fortunately some obese individuals will never develop diabetes, heart disease or cancer. The reason for this may be because these people do not have the typical low-grade chronic inflammation that other obese individuals exhibit. In fact, chronic low-levels of inflammation are associated with being metabolically unhealthy, regardless of weight. The reason why some people will have increased inflammation with weight gain, while others do not, is currently unknown. Unfortunately there is no easy test that determines whether an obese individual is among the few that will not have chronic inflammation, so the best health measure to take is to prevent weight gain. 5. Chronic inflammation in obese individuals may be caused by: aa. Fever. bb. Swelling. cc. Smaller adipose cells. dd. Macrophages. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 146 STUDENT RESPONSES Now that you know the mechanisms of type 2 diabetes and atherosclerosis, what types of foods and nutrients would you recommend to prevent these diseases? Hint: Think about ways to prevent obesity, as well as lower blood LDL. _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ ____________________________________________________________________________________________________ Remember to identify your sources _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ Wo r k b o o k Lesson 3.6 _____________________________________________________________________________________________________ ___________________________________________________________________________________________ 147 TERMS TERM For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 3.6 DEFINITION Atherosclerosis A disease of the arteries characterized by deposits of fat. Blot Clot A mass of coagulated blood. Cardiovascular Describes something that involves the heart or the blood vessels (arteries and veins). Diabetes Mellitus The most common form of diabetes. Caused by a deficiency in the action of insulin. Results in high blood glucose concentrations and urinary glucose excretion. Fatty Streak The first visibly obvious step in the development of atherosclerosis. Fatty streaks are made up of immune cells and lipoproteins (LDL). Gallstones Crystals of bile acids that form in the gallbladder that can cause sever pain and blockage of the bile duct. Heart Disease A structural or functional abnormality of the heart or blood vessels. Macrophage A large cell that is involved in the body’s immune response. Osteoarthritis A loss of cartilage in the joints that results in pain and stiffness. Plaque A region of fatty deposit on an artery wall that has been encapsulated by cells lining the arteries. Sleep Apnea A temporary stopping of breathing that occurs during sleep. Vascular Describes something that involves the arteries and veins. 148 Unit 4: Where are we heading? Unit 1: What’s in your food? Unit 2: How does your body use food? Unit 4: Introduction Unit 3: What is metabolic disease? Unit 4: How do I identify ‘good’ and ‘bad’ food? Unit 5: How does this knowledge apply to me? ______________________________________ In Unit 3 we learned that the concept of ‘fast’ or ‘slow’ metabolism is inaccurate, and that it is how our metabolic needs are balanced with our caloric intake rather than our metabolic rate that dictates whether or not we are at a healthy weight. We explored how the body regulates when and how much we eat, and learned that when the signals regulating hunger and the feelings of pleasure and reward become unbalanced, obesity can result. In this unit we focus on the messages we receive about ‘good’ and ‘bad’ foods. We will prepare to critically evaluate some examples of nutrition research in order to understand how the design limitations of nutritional research contribute to confusion behind some nutritional messages. 149 LESSON 4.1-2 WORKBOOK Why are there contradictory messages about 'good' and 'bad' foods? In these two lessons we begin to explore the processes and challenges of nutritional research. Sometimes foods or nutrients can be labeled as good one day, and bad the next. How can this be the case? In this lesson we will see that understanding how research studies are conducted impacts how we can interpret study results and may clarify apparent contradictions. All nutrition research has similar key components Wo r k b o o k Lesson 4.1-2 Even though nutrition research is quite diverse, all studies have the same core components: They ask a general BIG question, use scientific methods to answer that question, and result in data used to make conclusions that can advance our understanding of nutrition and disease. Here we will begin to walk through these main components. Later, in Lesson 4.3, we will learn about different methods used in nutrition research and we will explore how the methods limit the types of conclusions and claims we can make. Finally, in Lesson 4.5 we will work with published nutrition data to formulate our own claims based on the findings. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 150 LESSON READINGS Results Observa(on Scientific methods commonly used in nutritional science are iterative Although there is no single scientific method, most nutritional studies use common activities that are sometimes Background Experiment labeled the scientific method. But be careful, science Research is not a linear process and the scientific method is not intended to circumscribe an order for research, rather Hypothesis it entails components used in an iterative process. This means that the activities are modified and repeated as Figure 1: Components of the scientific we learn. When conducting research, scientists make method are used in an iterative process. observations that intrigue them or call what they know into question. They will often then turn to background research to see what others have found about the phenomenon. The observation and knowledge gathered by others can then be synthesized into a hypothesis. Based on this hypothesis, experiments can be planned and performed to test their theory. Finally, the data is used to make conclusions and update biological models. As we will see, how the experiments are constructed limits the scope of our conclusions, a factor often missed by reports of scientific findings in the news. Wo r k b o o k Lesson 4.1-2 We can use the discovery of the cause of scurvy as an example of methods used to understand disease. In the 15th and 16th centuries, European sailors often fell ill and died from scurvy. As mentioned in Unit 1, symptoms of scurvy include general discomfort and lethargy, spots on the skin, and bleeding spongy gums. Symptoms may also include paleness, depression and an inability to move. If the disease progresses open wounds develop and teeth fall out. A Scottish naval surgeon named James Lind observed how the sailors’ diet aboard a ship differed from their diets on land. Namely, far fewer fruits and vegetables were available onboard a ship. Hence, Lind found a correlation between high rates of scurvy and a diet with few fruits and vegetables, and hypothesized that scurvy was caused by a deficiency in some component of food. He then designed an experiment to investigate this possibility. The experimental conditions Lind established were to give sailors salt water, vinegar, cider, citrus juice or other liquids to drink. He found that the only the sailors who drank citrus juice were resistant to developing scurvy. From this he concluded that a component in the juice was able to replace the missing fruits and vegetables in the sailors' diets, hence preventing/ Figure 2: James Lind treating scurvy. We now know that the missing component replaced by conducted the first clinical trial to deterthe citrus juice is vitamin C. Today, investigators use similar processes mine what foods prevent to explore the relationship between food and health or disease. scurvy. 1. Which of the following is NOT true about the scientific method? aa. It is a set of steps that determine the order of scientific processes. bb. It is a steadfast rule that dictates how research is conducted. cc. It will produce results that will always be interpreted the same way. dd. It is an iterative process used to update biological models. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 151 LESSON READINGS The human factor DEFINITIONS OF TERMS Cell culture — A process in which cells are grown under controlled conditions in a laboratory. Research question — The primary question a scientific study is aimed to answer. For a complete list of defined terms, see the Glossary. In Unit 3 we briefly discussed how different methods used in research yield different conclusions. The same holds true for the overall type of study that was conducted. For example, did the study use human participants, or was the study carried out on animals, or on mice cells grown on a plate (cell cultures)? Each of these types of research has strengths and weaknesses. Using humans as research participants may seem like Figure 4: Using animal the most direct way to test the impacts of something in people. models has benefits like However, humans differ greatly from one another in both genetcontrolled environments and ics and lifestyle. So, depending on your research question genetics. However, a mouse is humans may or may not be the ideal participant! There are a mouse not a human! also several ethical issues that are raised when using humans as research participants. For example, it is unethical to purposefully cause a nutrient deficiency in people. Therefore, a study analyzing the effects of a nutrient deficiency would need to be conducted with laboratory animals, or in a human population that has a naturally occurring deficiency. It is also easy to determine the exact nutrient intake in mice, but very difficult to track the diet of free-living humans throughout the months or years of a study period. Given these limitations in human research, causal links between risk factors and a disease are often shown through experiments with animals and cell cultures. Unfortunately, conclusions that are made from animal or cell culture studies may not directly apply to humans simply because each of these organisms have Figure 5: Cell cultures grown on different biology. Hence, our limited ability to study human participants and a plate are useful in the significant biological differences between humans and other species biological research. has contributed to our evolving understanding of 'good' and 'bad' foods. The constant evolution of 'good' and 'bad' foods Are there really 'bad' nutrients? Wo r k b o o k Lesson 4.1-2 To further understand how the classification of 'good' and 'bad' foods is continually evolving we will take a look at the nutrients and foods that are commonly associated with disease (so-called 'bad' nutrients), and then explore how current research either supports or contradicts this classification. It is a common belief that diets high in fats, sodium, cholesterol and red meats increase the risk for developing heart disease. 2. Animal models are often used for nutrition studies because: aa. Using mice can avoid ethical limitations. bb. Diets of mice can be controlled. cc. Genetics of mice can be controlled. dd. All of the above. 3. Human-based studies are challenging because: aa. People have similar living habits. bb. People eat the same types of foods. cc. People misreport what they eat. dd. People have identical genetics. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 152 LESSON READINGS However there are many examples of nutritional studies that do not support these conclusions. To understand these discrepancies we will look to the experimental methods used in two studies to analyze the link between dietary fat and heart disease. Does dietary cholesterol lead to heart disease? Levels of low-density lipoprotein (LDL) in the blood correlate positively with increased rates of heart disease, and elevated blood LDL levels also correlate with diets rich in fats and cholesterol. From these data one may hypothesize that modifying diets to limit LDL levels will decrease the risk for heart disease. Figure 6: Dietary cholesterol is found in animal products, such as meat, dairy and eggs. Data published in 1972 in the American Journal of Clinical nutrition entitled Effect of dietary cholesterol on serum cholesterol in man supported this idea. In this study 70 male participants were fed diets that were identical in all aspects except for varying amounts of cholesterol. Men who consumed more dietary cholesterol had increased blood levels of LDL cholesterol, confirming a positive correlation between dietary cholesterol intake and blood LDL concentrations. But does this change in LDL correlate with a change in heart disease? The expectation was that lowering dietary cholesterol intake would thereby decrease blood levels of LDL (which the study confirmed), and as a consequence the risk of heart disease would also decrease. However, lowering dietary cholesterol can have the opposite effect, leading to increased incidence of heart diseases! As recent data suggests, LDL is not the only character in the heart disease story. It turns out that low levels of HDL positively correlate with risk of heart disease, suggesting that perhaps the ratio of HDL to LDL may be important. This may explain why low cholesterol diets can have negative effects on heart diseases; a low cholesterol diet may lower both LDL and HDL. Wo r k b o o k Lesson 4.1-2 Figure 7: The HDL to LDL ratio may be more effective at determining heart disease risk than HDL or LDL alone. What happens to the HDL/LDL ratio when people eat low fat and low cholesterol diets? In a study entitled Randomized Clinical Trials on the Effects of Dietary Fat and Carbohydrate on Plasma Lipoproteins and Cardiovascular Disease, reducing the levels of fat intake overall seems to lead to a reduction in both LDL and HDL cholesterol levels, and an increase in blood triglycerides. So a diet with less total fat can reduce heart disease risk by lowering LDL, but at the same time it increases heart disease risk by lowering HDL and increasing triglycerides. Based on these studies, would you classify dietary fat and cholesterol as 'bad' or 'good'? 4. High LDL cholesterol is correlated with heart diseases. Therefore, reducing dietary LDL: aa. May cause heart disease. bb. May prevent heart disease. cc. May have no effect. dd. All of the above. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 153 LESSON READINGS The parts don't equal the sum of the whole! DEFINITIONS OF TERMS Incidence — The occurrence, rate, or frequency of a disease. Osteoporosis — 'Porous bones'. A condition in which the bones become brittle and fragile from loss of tissue. Placebo — A substance with no therapeutic effect that is used as a control in a study. For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 4.1-2 In many cases it is difficult to determine what component of food is causing or preventing a disease or ailment. Even if the causal nutrient is identified, it often has different effects when eaten in the absence of the other components of the whole food. For example, imagine that you make the observation that women who drink at least three cups of milk a day have a lower incidence of osteoporosis than those who don’t drink milk Figure 8: Supplements may not have the at all. Milk is high in calcium, an important same biological activity as whole foods rich building block of bones, so you design a in the nutrient. study to test the hypothesis that calcium intake will prevent osteoporosis. In this study, women are randomized to take either a calcium supplement or a placebo, after which bone density is measured. Unfortunately you find no effect, so you conclude that calcium intake is not related to bone density. However, calcium in milk is in a complex mixture of lipids and other vitamins including vitamin D, which investigators later found are required for the calcium to be absorbed effectively. Hence, the results from the study of calcium alone may be reported in the news as 'increasing calcium intake does not prevent osteoporosis'. But years later, after the discovery that calcium intake is vitamin D-dependent, the study may be reported as 'increasing calcium intake does prevent osteoporosis'. Which statement is correct? Or are they both correct or both incorrect? 5. The conclusions of a nutrition study are definitive and cannot be changed. aa. True. bb. False. 6. The results of a study analyzing the effect of a nutrient can be different than analyzing the effect of a whole food. aa. True. bb. False. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 154 STUDENT RESPONSES What are the pros and cons of conducting nutritional studies in humans vs. mice? _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ ____________________________________________________________________________________________________ _____________________________________________________________________________________________________ Remember to identify your sources _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ Wo r k b o o k Lesson 4.1-2 ___________________________________________________________________________________________ 155 TERMS TERM For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 4.1-2 DEFINITION Cell Culture A process in which cells are grown under controlled conditions in a laboratory. Incidence The occurrence, rate, or frequency of a disease. Osteoporosis 'Porous bones'. A condition in which the bones become brittle and fragile from loss of tissue. Placebo A substance with no therapeutic effect that is used as a control in a study. Research Question The primary question a scientific study is aimed to answer. 156 LESSON 4.3 WORKBOOK How do we know what 'good' and 'bad' food really is? DEFINITIONS OF TERMS Interventional study — A study where a treatment or intervention is assigned to select participants. Observational study — A study where no treatment or intervention is assigned to participants, but rather entails scientists observing patterns and trends of humans and human diseases. Here we will further explore the idea that the way a research study is done plays a significant role in the types of conclusions we can draw from the data. We will first discuss types of studies and their limitations. Next, we will discuss the types of bias and confounding variables that are commonly associated with nutrition studies. Types of research studies For a complete list of defined terms, see the Glossary. Figure 1: In observational studies researchers simply watch and analyze a population’s behavior for correlations. Wo r k b o o k Lesson 4.3 In the previous lesson we began to discuss some pros and cons of human, animal and cell culture based research. We will now go into more detail about the different types of studies and their limitations. Overall, there are two types of studies: observational and interventional. Observational studies compare groups or measure something over time without interfering in the groups’ behavior. For example, epidemiological studies are observational and are excellent for finding correlations. In contrast, interventional studies compare a group that receives a treatment or intervention with a control group that does not receive the treatment or intervention and are used to question causation. 1. A study where researchers compare the diets of diabetic people to diets of a healthy population is: aa. An interventional study. bb. An observational study. cc. A case control study. dd. B & C. ee. All of the above. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 157 LESSON READINGS Epidemiological studies reveal useful human patterns DEFINITIONS OF TERMS Epidemiology — The study of patterns, causes and effect of health and disease in defined populations. For a complete list of defined terms, see the Glossary. There are a number of methods used to study diseases in humans, all of them seek to identify and then investigate the distribution and patterns of specific factors that are thought to relate to health and disease. One way to conduct human research is to follow a population and look for patterns in their behavior and health. When these epidemiological studies Figure 2: Epidemiologists reveal patterns, other studies can be done to understand what observe the health of large the pattern means and to propose targets for preventative populations. medicine. Not all methods of epidemiologic studies are created equal, as we shall see. Most of them are only able to provide purely correlative data, which is unable to show causative links that conclusively connect a factor to a disease. Some of the different types of epidemiological studies are: ■■ Case studies: The study of a single person or a small group of people. Small numbers of subjects means that this type of study is invariably descriptive. ■■ Migrant studies: Examine how peoples’ health changes as they move from one country to another. ■■ Cohort studies: Compares a population at risk for a disease with a group without those risk factors. Both populations are followed over time and correlations are made between those that get ill and those that stay healthy. ■■ Case control studies: Again, diseased populations are compared with healthy populations. In this case, genetic or lifestyle factors that correlate with disease are investigated. Wo r k b o o k Lesson 4.3 In all observational studies it is possible to generate alternative explanations for the patterns you find. This is because there could be factors impacting the pattern that you don't know about, so called confounding variables. Making a broad conclusion and health recommendation based on correlative data like these may in large part explain the constant re-categorizing of ‘good’ and ‘bad’ foods. Figure 3: Correlations don't reveal how factors interact. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 158 LESSON READINGS Moving from correlation to causation: Interventional studies So how do you go from correlations and observations to understanding how factors relate? For example, alcohol consumption is highly correlated with lung cancer incidence. What does this mean? Does drinking alcohol cause cancer or do people that drink alcohol have something else in common that leads to cancer? To sort out the relationship between factors, interventional studies must be done. Figure 4: Alcohol consumption is correlated with lung cancer. What does this mean? Interventional studies are used to sort out the relationship between factors like this. As we discussed in the previous lessons, human participants cannot be used for every type of nutrition study. Laboratory animals more readily adhere to difficult diets or treatments than humans. Additionally, many of the factors that cause variability in human research (like genetic variability or lifestyle factors) are not a problem in animal studies. There are still some types of nutrition studies that monitor human study participants for 24 hours a day, but this brings up obvious logistical and financing problems. Because more details about the physiology of a process can be attained from cell culture or animal studies, you may think that those study models may be the best place to begin research into a topic. Conversely, most research questions begin at the human level and work their way backwards. Epidemiological studies are used to identify correlations, and then animal or cellular models are used as intervention studies. If the animal models are promising, researchers may move to expensive timely interventional studies in humans. Wo r k b o o k Lesson 4.3 Figure 5: Mice are often used as a model in nutrition studies. For example, one group of scientists may find a correlation between increased obesity and increased incidence of type 2 diabetes. Other scientists will use these observations to formulate the research question Does obesity cause insulin resistance? To answer this question, they may design an intervention study in using an animal model where they induce obesity in mice and watch to see if they develop insulin resistance. This type of experiment would not be ethical in humans, so the following human intervention may be to randomly have obese insulin resistant patients placed into weight loss programs to see if weight loss leads to normalization of insulin resistance. 2. Correlative studies can be used to: aa. Find patterns linking a factor to disease. bb. Find causes of disease. cc. Understand how a factor impacts disease. dd. All of the above. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 159 LESSON READINGS Moving from correlation to causation: Randomized, controlled trials are the golden standard DEFINITIONS OF TERMS Double-blinded study — Takes a population of subjects and randomly assigns them to a treatment or control group. Neither the subjects nor the researchers are aware who is in the treatment group, and who is in the control group. Meta analysis — Results from multiple studies are combined and re-analyzed to determine whether a pattern exists among all study results. Randomized control study — Randomizes a population of study participants to either a control or an intervention group. For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 4.3 To identify whether one factor causes another, the randomized controlled study, or a doubleblinded study is the golden standard. There are three parts that make up a strong interventional study: It is randomized, it has an appropriate control group, and it is double blinded. First, participants are randomly put into an experimental or a control group. This is intended to avoid any bias that may come from selecting participants. Second, to ensure that neither the participant nor the researcher can knowingly bias the results of the study, both are blinded about their being in the experimental or control group. Figure 6: In human interventional studies, participants are randomly assigned to a treatment or control group. Randomized controlled studies are the preferred methodology for human research, however they are not always possible because they are very expensive, are conducted for a long period of time, and a proper control may not always be available. In addition, if you find that your treatment group is doing better or worse that the control group it is un-ethical to continue the study, because all people disserve the best possible care. Lumping many studies into one can summarize research data It is important for scientific findings to be confirmed by multiple groups. The type of analysis in which the results from multiple studies are compared is called a meta analysis. Meta analyses can be used to explore whether there is a consensus between findings from different studies. Meta analyses of randomized controlled studies that reveal strong consensus between studies, and should be the basis for health recommendations that are suitable Figure 7: Each type of study has pros and cons that limit usability for large populations. and the types of conclusions you can make. 3. A study where people are randomized to receive either a vitamin supplement or a placebo is: aa. An interventional study. bb. A randomized controlled trial. cc. A human study. dd. All of the above. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 160 LESSON READINGS What variables can alter study results? Variability in human research DEFINITIONS OF TERMS Epigenetics — The study of heritable changes to the DNA that alter gene expression. For a complete list of defined terms, see the Glossary. Figure 8: Our genetics, lifestyle, and other factors all contribute to variability in humans. People come in many shapes, sizes, genetic backgrounds and types of upbringings. Add to that the variety of diets and types of foods consumed worldwide and you may begin to understand one of the primary challenges in nutrition research. A study that is conducted in one set of humans, white post-menopausal women for example, may not apply to other populations. Some primary factors that make humans different from one another are: ■■ Genetics: While 99.9% of our DNA is identical, the differences in the other 0.1% are often big enough to make large, population studies difficult. Our genetics can change how we metabolize, transport and store macro and micronutrients. For example, some people naturally have very high HDL in their blood, and some have very low HDL, depending on their genetics. This in turn can alter the risk for heart disease. ■■ Lifestyle factors: More than just the type of diet each person consumes, other lifestyle factors can have a significant effect of the overall health of a person. These may include the amount of physical activity, the hours of sleep at night, the level of stress, and others. ■■ Region of residence: People living in different corners of the world have different access to healthful and harmful elements. Those that live in a city probably walk or bicycle more than someone living in a rural area, but may also be breathing in more pollution. Additionally, the synthesis of vitamin D in the body requires skin exposure to sunlight, which does not occur much in the winter in northern regions. Wo r k b o o k Lesson 4.3 ■■ Conditions during pregnancy: A relatively recent discovery has been that certain environmental exposures while a woman is pregnant can affect her child. This area of research, called epigenetics, asserts that the next generation can be 'programmed' before they even enter our world. Figure 9: Environmental factors during pregnancy, like diet, can program the fetus to metabolize nutrients differently. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 161 LESSON READINGS ■■ The microbiome: We have heard of the microbiome in previous units. Remember that the microbiome refers to the microorganisms that live all over our bodies, including in our gut and on our skin. This diverse array of bacteria in our intestine can metabolize nutrients differently, possibly causing variability in macro and micronutrient digestion, absorption and metabolism, and maybe even a persons weight. Confounding variables DEFINITIONS OF TERMS Confounding variable— A variable that correlates with both of the dependent and independent variables of a study. For a complete list of defined terms, see the Glossary. A confounding variable is an element in the research that is either impossible to eliminate, or was overlooked by the researcher. By remaining in the analysis, a confounding variable can damage the validity or credibility of an experiment, therefore it is important to Figure 10: A confounding variable can mislead our interdetermine as many confounding pretation of causation from correlative results. variables as possible before beginning a study. You can think of a confounding variable as a factor that is usually coupled with one of the variables of the study. For example, as discussed above alcohol consumption is linked to lung cancer, but what variable is missing? In fact, alcohol consumption is linked to smoking because people that smoke cigarettes are more likely to drink alcohol. So you could not effectively study the correlation between alcohol consumption and risk of cancer without also taking into account whether the study participants are smokers. Another example is if you were planning a study to research the benefits of a calcium supplement on preventing osteoporosis, it would be necessary to take the location of the research into account. Because vitamin D is required for calcium absorption from the small intestine, and exposure to sunshine is required for vitamin D synthesis, people living in a sunny location may respond better to a calcium supplement than people living a cloudy region. In this example, the location of the study is the confounding variable. A well-planned study will eliminate most of these confounding variables but it is impossible to know what you don't know! This is why correlations can be dangerously misleading. Wo r k b o o k Lesson 4.3 4. Human variability caused by access to healthy food is an example of: aa. Genetic variability. bb. Lifestyle factors. cc. Conditions during pregnancy. dd. The microbiome. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 162 LESSON READINGS Bias can alter the results of research In addition to confounding variables, there are other errors in study design that can alter the results of a study. Confounding variables are one type of bias, with the other two primary forms being: DEFINITIONS OF TERMS Information bias — A bias created in scientific data by having incorrect information, or from making a measurement error. Selection bias — An error in choosing study participants creates a bias in the data. For a complete list of defined terms, see the Glossary. ■■ Selection bias: This occurs when subjects in a study are selected as a result of a third, unmeasured (or immeasurable) variable. For example, studies often have limited participant diversity — race, gender, economic status, education, and numerous other variables may also be having an effect. ■■ Information bias: This occurs when there is a systematic error in how a variable is assessed. This is of particular importance in nutritional studies, because participant compliance with experimental conditions is often difficult to ensure. For example, imagFigure 11: Including only one gender, ine you were researching the link between race, age group or education level in a high fat diets and colon cancer. To investistudy is selection bias. gate this you use a double-blind study with a control group and a group that is asked to limit their fat intake, and you monitor the progress using a survey. After years of collecting data you fail to see a correlation between fat intake and colon cancer incidence. This lack of association may be caused by a true effect, or simply because your study participants did not limit their fat intake as much as they said. When you are reading through a scientific article try to identify the biases that were controlled for, and those that were overlooked. The better the study, the fewer you will find! Wo r k b o o k Lesson 4.3 5. Conducting a study where all of the participants are recruited from college campuses is an example of a(n): aa. Observational study. bb. Migrant study. cc. Selection bias. dd. Information bias. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 163 STUDENT RESPONSES Imagine you are designing a study to analyze whether there is an association between the average distance a person walks in a day and the risk of obesity. What types of challenges might you find in your study design? What types of human variability, confounding variables, and bias may you find? _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ Remember to identify your sources ____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ Wo r k b o o k Lesson 4.3 _____________________________________________________________________________________________________ ___________________________________________________________________________________________ 164 TERMS TERM For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 4.3 DEFINITION Case Control Study This type of study follows participants that already have the disease under consideration and compares them to healthy subjects of a similar demographic. Case Study A study or anecdote involving a single person or a very small group of people. Case studies are usually used as examples of a relationship, but do not provide sufficient scientific data and results to validate a finding. Cofounding Variable A variable that correlates with both of the dependent and independent variables of a study. Cohort Study A study that follows participants whom are at risk for the disease under investigation over time. Cohort stud ies give insight into disease progression, but there is no intervention. Double-Blinded Study Takes a population of subjects and randomly assigns them to a treatment or control group. Neither the subjects nor the researchers are aware who is in the treatment group, and who is in the control group. Epidemiology The study of patterns, causes and effect of health and disease in defined populations. Epigenetics The study of heritable changes to the DNA that alter gene expression Information Bias A bias created in scientific data by having incorrect information, or from making a measurement error. Interventional Study A study where a treatment or intervention is assigned to select participants. Meta Analysis Results from multiple studies are combined and re-analyzed to determine whether a pattern exists among all study results. Migrant Study Looks at changes in health as people move from one country to another. Migrant studies can provide useful information about how a lifestyle that is associated with a country or population can affect health outcomes. Observational Study A study where no treatment or intervention is assigned to participants, but rather entails scientists observing patterns and trends of humans and human diseases. Randomized Control Trial Randomizes a population of study participants to either a control or an intervention group. Selection Bias An error in choosing study participants creates a bias in the data. 165 LESSON 4.4 WORKBOOK Seeing through the static — How do we identify correlations in data? Number of Shark A4acks In this lesson we will learn more about some of the statistics that are used in scientific research. We will see how researchers sort through scientific data in search of potential factors that link diet to health outcomes. We will explore how primary data addresses questions like ‘what is a significant correlation?’ and ‘How might this data impact our ideas about factors that contribute to or protect against heart disease?’ Wo r k b o o k Lesson 4.4 Correlation does not mean causation! What is the difference between two variables that are correlated, and a cause and effect relationship? Ice Cream Sales Figure 1: Just because ice cream sales and shark attacks are correlated, it does not mean that ice cream sales cause shark attacks! Have you ever heard people declare that every time they wash their car, it rains? While this may seem to be true, it certainly is not likely that washing a car is what is causing rain to fall. There may be a correlation between timing of the car wash and the weather, but there is no causal relationship. This delineation may sound simplistic, but the confusion between correlation and causation can puzzle even the most well versed scientists. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 166 LESSON READINGS A correlation is simply an association between two factors. On the other hand, a causal relationship means that one factor depends on the other. As we saw in the last lesson, the type of study determines whether the results can show correlative or causative relationships; observational studies can only provide correlative data, whereas interventional studies can provide causative data. The type of study determines the type of results: The chicken definitely came first, I think? Observational studies can only provide correlative data, whereas interventional studies can provide causative data. Because many human studies in nutrition research are observational, they can only show correlations between a nutrient and a health outcome. Additionally, many causative relationships have only been demonstrated by an animal model or cell culture study. So how can we make educated decisions about what the results mean for humans trying to live a healthy life? In order to prove that one variable (the independent variable) causes another (the dependent variable), the timing has to be right. This means that the change in the dependent variable must follow the change in the independent variable. If your independent variable was a meal, for example, and the dependent variable was blood glucose concentrations, you would see that after someone consumes a meal their blood glucose concentrations will rise. Correlative data often gets misinterpreted as causative data Wo r k b o o k Lesson 4.4 Figure 2: Eating food coloring is correlated with hyperactivity but may not cause it. Some nutrients and foods get a reputation for being 'bad', while others are known as 'good'. Most of these assumptions are based on correlative data. There are many instances where consumption of a nutrient or food correlates with some health outcome. For instance, increased consumption of some artificial food colorings correlates with hyperactivity in children, but the mechanism that would explain how the food coloring is causing hyperactivity has not been established. Even so, the belief that the food colorings are the 'cause' for hyperactivity is strong enough to make parents avoid the chemicals, and has led the FDA to review the safety of food dyes. When reading a news article describing study results, ask yourself whether the results are truly demonstrating a cause and effect, or whether there might be alternative explanations for the results. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 167 LESSON READINGS Statistics are used to measure correlation, not causation Strong results come from good sample selection DEFINITIONS OF TERMS Mean — The mathematical average of all samples in a data set. Median — The numerical value that separates the higher half of data from the lower half. Population — An entire collection of people or animals of interest from which data is collected. Representative sample — A subset of the greater population of interest that accurately reflects the members of the entire population. Standard deviation (STD) — Indicates the variability or deviation for an experimental group. For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 4.4 If we wanted to learn what the common blood glucose concentration is after eating a specific food, we could not possibly measure every single person’s blood glucose. How then do we gather generalizable research findings? One way to do this is by selecting a Figure 3: You can't measure representative sample. This sample should include a everyone so you need to select a random selection of people that represent the greater sample group to study. population. We use samples as estimates of the whole population, but we will never be able to know the results of an entire population without making the measurement on everybody. It is common to find different results when using different representative samples simply because of the variability among human participants. If the representative sample chosen was truly characteristic of the greater population, it should provide a reliable estimate of what results we can expect in the population. Let's say you pick a perfect sample group, how do you know if your findings are real rather than random? If a person flips a coin 100 times and gets 85 heads, what are the odds that that would happen? An important concept is that statistics can be used to measure the probability that your findings are sheer dumb luck! Common statistical methods Learning about statistics may seem daunting at first, but it can be easily grasped after we learn a few simple concepts. Some key ways we can summarize data include: Mean Family Income ■■ Average/Mean: The value that represents the calculated central value of a data set. Calculated by adding up all of the values and dividing by how many numbers there are. Median Family Income ■■ Standard Deviation (STD): A measure of the variability of the data around the mean. If you have ten observations that are identical the STD is small. If you have ten observations that are all different the STD will be large. 60,000 ≠ 44,000 Figure 4: If data is not normally distributed, mean and median can be very different. ■■ Median: The middle number in a set of data if you sort the numbers from smallest to largest. This helps you find the most common observation rather than the average one. For example, in the US the average family income is 60,000 dollars but the median family income is 44,000 dollars. Why are they so different? Think Bill Gates! 1. What is the difference between a representative sample and a population? aa. The sample is smaller. bb. The population includes every person of interest. cc. The sample is used in scientific studies. dd. All of the above. 2. What is the likely cause of a sample population not representing the entire population? aa. The sample size is too small. bb. Selection bias of the sample. cc. The sample was not randomly selected. dd. A & B only. ee. B & C only. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 168 LESSON READINGS DEFINITIONS OF TERMS Normal distribution — Also called a 'bell curve'. Represents the distribution of many random variables as a symmetrical bellshaped graph. For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 4.4 When we plot a graph to show the distribuAverage$ tion of data they can make different shapes. Sometimes data can be skewed to one side, or have several peaks and valleys. Often the Bell$Curve$ distribution of data will make the shape of a hand bell, with no bias to the left or the right (as shown in Figure 5). When this occurs the majority of data will fall in the middle of the graph, with a symmetrical tapering as you move away from the center. This type of distribution is called a normal distribuFigure 5: The normal distribution looks like a tion, or a bell-shaped curve. Many simple bell, and is sometimes called a 'bell curve'. examples of a data set will make a normal distribution, such as the heights of a group of people, blood pressure, or the grades in a classroom. The shape of the distribution is an important thing to consider when you of compare data from two groups. When the distribution is normal the average will be close to the median, but when the distribution is skewed the average will differ from the median, just like the income example given above. Comparing groups As long as the distribution of data in both experimental groups is the same shape, we can use statistics to measure how different the two groups are. If the two groups of data do not differ from one another, they would overlap on a graph when plotted. The more different the data sets are, the further apart their distriControl Treatment butions will appear on a graph, as in Figure 6. After Group Mean Group Mean statistically determining whether the data distribution of the experimental groups is the same or different, you Figure 6: Group means can be will be able to either accept or reject your hypothesis. compared if both groups have similar Let's again use blood glucose concentrations after distributions. a meal as an example. An experimental hypothesis may be that people who are obese will have higher blood glucose concentrations two hours after a meal than people who are lean. Statistics will be able to determine how different the blood glucose levels are between the groups. But remember, statistics only measures how different groups are not whether the variables are correlated or causative! 3. The mean and the median are the same: aa. In all data sets. bb. If the data are distributed normally. cc. If the distribution of the data is skewed. dd. All of the above. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 169 LESSON READINGS DEFINITIONS OF TERMS Coefficient of determination — Also called 'r-squared'. Indicates how well data points fit a straight line. P-value — The probability of obtaining a test statistic at least as extreme as the one observed if the hypothesis were false. For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 4.4 Figure 7: Statistical significance shows how related or different data sets are, not how likely the hypothesis is to be correct. A statistical measure called a p-value helps you determine the significance of your results. As a reader, you can look for the p-value to determine if the differences between groups are significant. The smaller a p-value is, the greater the difference is between the groups. For example, if you do the blood glucose concentration experiment above and find a p-value of 0.01, that means that there is a probability of 1 in 100 that these observation happened randomly. In other words, there is a 1 in a 100 chance that the blood glucose concentrations of the two groups are the same, so we can say with confidence that the groups are significantly different. For biological research, a p-value of 0.05 or less is considered significant. Statistics can be used to describe correlations We have talked a lot about correlations, but what does a Posi%ve No Nega%ve correlation look like? Variables Correla%on Correla%on Correla%on can be positively or negatively correlated. A positive correlation means that as the value of one variable increases, so does the value of the other factor. The temperature outside may be positively correlated with your Figure 8: When two variables are plotted they can somedesire to go to the beach, for times have a linear relationship, which demonstrates correlation. If there is no linear shape, there is no correlation. example, whereas the temperature is probably negatively (or inversely) correlated with your desire to cozy up next to a fire. The coefficient of determination, or r2 (r-squared), is used to describe the variability of the data from the linear correlation. In other words, if you plot the variables in against each other do you get a line or a blob? Data that is very scattered (blob like) when plotted will have an r2 close to zero, and data that makes an almost perfect line when plotted will have an r2 close to 1. You can think of r2 as representing the percent of the data that is closes to a line of best fit. For example, if the r2 = 0.75, then 75% of the data is in a linear relationship with one another. 4. A significant p-value means causation has been proved. aa. True. bb. False. 5. Two variables are correlated when: aa. One causes a change in the other. bb. A statistical difference isn't found. cc. They have a linear relationship when plotted. dd. Their coefficient of determination (r2) is less than 0.01. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 170 STUDENT RESPONSES Let's say you are observing two groups, one with a BMI over 30 and the other with a BMI between 20 and 25. You find that the BMI 30+ group has higher LDL cholesterol than the 20-25 group with a p-value of 0.001. What type of conclusions can you make based on this information? (Please draw graph(s) to help with to explanation.) __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ Remember to identify your sources __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ __________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ Wo r k b o o k Lesson 4.4 _____________________________________________________________________________________________________ ___________________________________________________________________________________________ 171 TERMS TERM For a complete list of defined terms, see the Glossary. Wo r k b o o k Lesson 4.4 DEFINITION Coefficient of Determination Also called 'r-squared'. Indicates how well data points fit a straight line. Mean The mathematical average of all samples in a data set. Median The numerical value that separates the higher half of data from the lower half. Normal Distribution Also called 'bell curve'. Represents the distribution of many random variables as a symmetrical bell-shaped graph. P-Value The probability of obtaining a test statistic at least as extreme as the one observed if the hypothesis were false. Population An entire collection of people or animals of interest from which data is collected. Representative Sample A subset of the greater population of interest that accurately reflects the members of the entire population. Standard Deviation Indicates the variability or deviation for an experimental group. 172 LESSON 4.5 WORKBOOK Treating obesity with behavior modification? In Unit 4 we have been learning about how experimental results are often misinterpreted because of the confusion surrounding statistics, correlation, and causation. In this lesson we will incorporate that knowledge into a larger skill: How to read a scientific article. Here, we will focus on the different parts that make up a scientific article, and what information they provide, building on the QMDC discussed in Lesson 3.5. How to read a scientific article Wo r k b o o k Lesson 4.5 Figure 1: To evaluate a health claim you need to know the foundation of the claim. Reading and understanding formal scientific articles is a skill that all doctors and scientists acquire over time. By learning how to critically examine these articles, you are open to a new world of information. The ability to read and understand scientific articles allows us to evaluate the evidence behind health claims. If you want to know if the news article got it right, or if the latest diet fad makes any biological sense, look at the study design and the data! If the experiments are observational the best they can show is a strong correlation, does this convince you to make life style changes? ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 173 LESSON READINGS There are two primary types of scientific articles: primary research articles and review papers It’s a duck! No, it’s a rabbit! Primary research articles are reports of new research that address a very specific research question. These articles are usually what get the most media attention because they reveal new findings. Review articles tend to be broader, and instead of presenting new information they tie several studies together and make larger conclusions. Figure 2: Scientific data does Review articles are helpful when you are trying to learn not become invalid over time but what the general consensus is about a topic. When you our view of it may change. are reading either type of scientific article keep in mind that the more recently published primary research articles are presenting novel ideas that may not be validated by other researchers, and that the older review articles may include ideas that have since been disproven. Also keep in mind that scientific data do not become less accurate when they are out of date, rather, as our knowledge grows our interpretation of results may change. For example, if you are asked to describe a basketball court from the floor your description, although accurate, will differ from the description of someone sitting high up in the bleachers. This is often the basis for two research articles that make opposite conclusions; the results of both can be accurate, even if the conclusions differ. Parts of a scientific article For the remainder of this lesson we will discuss the structures of primary research articles. In the same way that a book has a table of contents , chapters or a bibliography, research articles have a standard structure that can be used to navigate the article. When you are reading a research article you may want to read it out of the order it is written in to look for the information you want. Wo r k b o o k Lesson 4.5 Figure 3: Asking what the BIG question is before reading through a scientific paper will make the other parts easier to understand. Review From 3.5 - Using the QMDC method Reading a scientific paper is at first daunting, but it is a skill that grows with practice and is critical for understanding health claims. All primary science papers have a similar structure that we can use to navigate through the complex web of ideas. We can simplify the structure of a scientific paper into four parts, its QMDC: ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 174 LESSON READINGS Q uestion: What is the main question of the paper? M ethod: How do the authors investigate this question? D ata: The data is represented in figures, and each figure has its own QMDC. C onclusion: What conclusions can you make based on the data? Each paper has a primary, BIG Question that is usually reflected in the overall title of the paper. Then each figure in the paper asks a more fine-tuned Question that relates to an aspect of the big question. Each figure also uses a specific Method to address the big question. The Data from the figures allow us to draw Conclusions about whether the more limited questions have been addressed, which again relates to the BIG Question. As you read a paper you should be critical of everything and look for alternative explanations that could explain results. The scientists need to prove their case, and you are the judge, jury and ......! Importance of the title and authors Figure 4: Knowing the source of funding for a study may help you evaluate the credibility of the research. The title gives us a clue as to what the research is about. Often times the title includes the primary research question, and tells us whether the study was in humans, in animals or in a cell culture. It is also helpful to read the names of the authors and their institutional affiliations. Research conducted at a university or by a governmental organization is usually more credible and trustworthy than research that is conducted by an agenda-driven group, or a commercial endeavor such as a nutrition supplement company. Likewise, the source of funding for the research should be mentioned on all primary research papers, and can tell the reader whether there may be conflicts of interest. The Journal of Immunology The abstract summarizes the entire paper Jane Oliaro,*,† Vanessa Van Ham,* Faruk Sacirbegovic,*,† Anupama Pasam,*,† Ze’ev Bomzon,*,‡ Kim Pham, *,‡ Mandy J. Ludford-Menting,* Nigel J. Waterhouse,*,† Michael Bots,* Edwin D. Hawkins,* Sally V. Watt,* Leonie A. Cluse,* Chris J. P. Clarke,* David J. Izon,x John T. Chang,{ Natalie Thompson,|| Min Gu,‡ Ricky W. Johnstone,* Mark J. Smyth,*,† Patrick O. Humbert,# Steven L. Reiner,{ and Sarah M. Russell*,†,‡ Asymmetric cell division is a potential means by which cell fate choices during an immune response are orchestrated. Defining the molecular mechanisms that underlie asymmetric division of T cells is paramount for determining the role of this process in the generation of effector and memory T cell subsets. In other cell types, asymmetric cell division is regulated by conserved polarity protein complexes that control the localization of cell fate determinants and spindle orientation during division. We have developed a tractable, in vitro model of naive CD8+ T cells undergoing initial division while attached to dendritic cells during Ag presentation to investigate whether similar mechanisms might regulate asymmetric division of T cells. Using this system, we show that direct interactions with APCs provide the cue for polarization of T cells. Interestingly, the immunological synapse disseminates before division even though the T cells retain contact with the APC. The cue from the APC is translated into polarization of cell fate determinants via the polarity network of the Par3 and Scribble complexes, and orientation of the mitotic spindle during division is orchestrated by the partner of inscuteable/G protein complex. These findings suggest that T cells have selectively adapted a number of evolutionarily conserved mechanisms to generate diversity through asymmetric cell division. The Journal of Immunology, 2010, 185: 367–375. U pon activation, a naive T cell proliferates to generate the different T cell subsets required for both an immediate response and an immune memory (1). How the activation of a single-parent T cell can control multiple pathways of differentiation in the T cell progeny remains controversial. A parental CD8+ T cell, for example, may have the potential to develop into both effector and memory cells, with the outcome determined by extrinsic factors such as environmental signals or stimulus strength (2). Alternatively, T cells may divide asymmetrically after Ag presentation, leading to molecularly distinct daughter cells with different effector and memory fate potential (3–5). In vivo imaging has revealed much about the dynamics of T cell– dendritic cell (DC) interactions (6–8) and would be the ideal tool to analyze the molecular events after T cell conjugation with APCs and subsequent activation and proliferation. Although current technology using two-photon microscopy can accurately assess the duration of contacts and the functional consequences of these interactions (9–12), it does not have the resolution to assess the distribution of individual proteins in single cells. Fixed imaging analysis of dividing cells ex vivo in response to Listeria infection has revealed that asymmetric cell division (ACD) of T cells may dictate T cell memory and effector fates (4). However, in this approach, the history of the dividing cell is lost, making it difficult to extrapolate information about the mechanism of ACD, in particular, the cue for polarity. To overcome these limitations, we have developed an experimental in vitro system that enables the molecular analysis of single progenitor T cells undergoing their first division during interaction with an APC. This model provides an excellent system with which to image individual T cells undergoing division in response to contact with APCs, and evaluate the three requirements for ACD: 1) Downloaded from www.jimmunol.org on November 6, 2011 Wo r k b o o k Lesson 4.5 The abstract, usually around a paragraph long, is densely packed with the most important information in the study. The abstract will include a small amount of background about the topic, the hypothesis (Question), the general Methods, the Data and their Conclusions (QMDC). Asymmetric Cell Division of T Cells upon Antigen Presentation Uses Multiple Conserved Mechanisms Figure 5: The abstract is dense and may be best understood after you read the rest of the article. *Cancer Immunology Program, ||Bioinformatics, and #Cell Cycle and Cancer Genetics, ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 175 LESSON READINGS When you start-out in reading scientific articles you may find it helpful to skip the abstract until you finish reading the paper. Then, after you are more comfortable in sifting through terminology, you can more easily understand the abstract. The introduction gives us background information At the end of the introduction you should be able to identify the research Question and summarize the necessary background information to justify the importance of the research. The introduction provides background to help you understand why the topic and research is important and identifies a lack of knowledge that the paper's BIG Question/ hypothesis aims to fill. When reading several articles about the same research topic you may find overlap in the introduction sections. Even so, it is beneficial to read each introduction thoroughly because you will find the scientists’ motives for the research and their expected outcomes. The methods tell us how the researchers explored their hypothesis Wo r k b o o k Lesson 4.5 After you have identified the BIG Question, you can start to sort out how the researchers are going to answer that question. Usually, the BIG question is broken down into several smaller Questions or study objectives. The overall study design will be explained here, which is where you can find whether the experiment was observational or interventional. The Methods should be written with enough detail so as to allow another scientist to copy the experiment exactly. The Methods section of a research article may be the most difficult to understand, because it will include many words and techniques that you are unfamiliar with. It can sometimes help to keep a running list of unknown terms and look up the definition of each one separately. Be patient as you read through the Methods, because understanding how the experiments are done is the key to interpreting the results. Figure 6: Research articles are confusing at first, but they have structures you can use to navigate the material! ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 176 LESSON READINGS The most important results will be in a figure or table ournal of Immunology rs (2). After treatment with IL-2 and IL-15, naive CD8+ T cells 2Lhi, CD44med, CD692, CD252, Supplemental Fig. 8) develinto subsets characteristic of effector (CD62Llo, CD44hi, med , and CD25hi) and memory cells (CD62Lhi, CD44med, lo , and CD25med), respectively (Fig. 2C). Treatment of the –DC conjugates with ATM 20 h prior to first cell division o effect on differentiation into effector T cells, as assessed ch of the four markers (Fig. 2C, compare first and second In contrast, after treatment with 40 mM ATM, the cells culin conditions designed to induce memory differentiation d a shift toward a more effector-like phenotype with upreguof CD44 and downregulation of CD62L (Fig. 2C, compare and fourth row). No differences were observed for CD69 and expression between untreated and treated T cell–DC conjuThese data suggest that ACD, regulated by the polarity netmight impact on T cell fate decisions. olarity cue for ACD requires contact with the DCs, but stained polarization of classic immunological synapse rs during mitosis Wo r k b o o k Lesson 4.5 of T cells uses conserved mechanisms to coordinate ty with the orientation of the spindle requires not only polarization of proteins, but also alignof the mitotic spindle with the axis of polarity (14, 15). In It is tempting to try to make your own conclusions about the study as you read through the results, but ultimately it is best to first understand each result on its own before you lump them together into a larger conclusion. You will find that the majority of the results are summarized as tables and figures. Ask yourself these questions when you look at each figure or table: What is the Question, what Methods were used, what does the Data show, and what Conclusions can you make about the data in just that figure. It is also important to question the results: What samples were Figure 7: Each figure used? How big was the sample size? Are the results correlative or has a QMDC that relates causative? If the words “significant” or “non-significant” are used to to the BIG Question. describe a result, what does that mean? Can you come up with an explanation for the results besides the ones the authors provide? Finally, try to link each result back to the overall BIG Question and the smaller study questions or study objectives. Did the authors convince you that their Conclusions are sensible? Conclusions and discussion Downloaded from www.jimmunol.org on November 6, 2011 ext investigated how the polarity cue provided by the DCs is mitted to the dividing T cell. Cells such as the fertilized Caenoitis elegans zygote retain memory of a previous polarity cue, and se cells polarity is maintained by proteins such as Par3 (14, 36). symmetry previously observed in mitotic cells separated from t with APCs suggests a similar possibility for T cells (4). Indeed, cent identification of a molecule, CRTAM, which can interact Scribble to sustain CD3/CD28-Ab–mediated polarity after the ave disengaged, supports this notion (37). We therefore investithe dependence of the asymmetric localization of aPKC, Par3, le, and Numb on the interaction with the APC at the time of s. The distribution of fluorescence in dividing T cells attached to was compared with the distribution of fluorescence in the rare aptured dividing while unattached to a DC. In the absence of DC, , Par3, Scribble, and Numb were not polarized (Fig 3). This sts that, where ACD is controlled by Ag presentation, memory contact is not sufficient for polarity at the time of division, and ontact with the DC is necessary not only to establish polarization nitiation of Ag presentation, but also to maintain this asymmetry h to the onset of mitosis. presentation initially involves the formation of an immunol synapse, with the recruitment of T cell receptor-associated ing molecules and the microtubule organizing center (MTOC) interface with the DCs (38). We therefore determined whether ns that are normally associated with the immunological synmight transmit the polarity cue from the DCs, by assessing er they are also polarized to the interface in the dividing s. CD8 was not polarized to the proximal cell at either early mitosis, but showed localization to some distal cells in early s. LFA-1 was enriched at the contact site in early mitosis but id not result in significant polarization to the proximal cell. ver, the synapse marker, PKCu and distal pole marker, , were significantly polarized in early mitosis (Fig. 4). The ely even distribution of all these proteins at late mitosis sugthat, although the immunological synapse might play an imt role in dictating the axis of polarity (perhaps related to the tment of the MTOC to the interface), differential inheritance of receptor-associated signaling molecules is unlikely to be imt for fate determination in this system. 371 This is the final section of content in a research article and it is here that the authors will interpret the results of the study. The authors will write what they think their results mean, but this does not mean that they are correct. Sometimes your own interpretation of the results will be different than some instances, such as divisionand of Drosophila male germ the researchers, that’s okay! Thecells, more alternative ways the orientation of the mitotic spindle is defined by the polarization of the MTOC at interphase duplication, centrosome you can think (39). of toAfter interpret theoneresults, the better you will remains anchored in this position by microtubules, and the other understand relocates to the oppositethe side research. of the nucleus (39, 40). The stable FIGURE 3. ACD of T cells requires contact with the APC. The ratio of proximal/distal polarization was assessed as in Fig. 2 for aPKC (24 cells), Scribble (14 cells), PAR-3 (8 cells), and Numb (10 cells) in mitotic cells unattached to a DC (representative images below) compared with mitotic cells attached to a DC. Tubulin (red, Alexa-546) and aPKC, Par3, Scribble, and Numb (green, Alexa-488). Images were collected with a 603 oil immersion objective as indicated in Materials and Methods. Scale bars, 10 mm. recruitment of the MTOC to the interface with the DCs raised the possibility that it might also orientate the mitotic spindle during mitosis. However, staining of fixed, dividing T cell/DC conjugates for a-tubulin was not compatible with this, as the tubulin condensed in the center of the cells before the centrosomes separated to opposite poles of the cell (Fig. 5A, 55 of 60 cells at prophase were in the central third of the cell, with five slightly distal). An alternative means of dictating spindle orientation links Dlg to trimeric G protein signaling to coordinate the orientation of the spindle body with the axis of polarity (41). In Drosophila neuroblasts, Dlg can recruit Pins (partner of inscuteable, also known as LGN in mammals) (31, 42) which in turn reinforces polarity and orients the spindle of neuroblasts and mammalian neuronal precursors by binding to GaI (41, 43, 44). We found that Pins (45) was expressed in T cells (Supplemental Fig 9), and polarized to the distal side of the asymmetrically dividing T cell (Fig. 5B). To assess whether the Pins/G protein pathway regulated spindle orientation in T cells, we attempted to disrupt G protein signaling by sequestering Gbg proteins with overexpression of the b-adrenergic receptor kinase C-terminal domain (b-ARK) (16). Besides interpretation of the results, the conclusion and discussion portion of a research article will sometimes contain other information as well. Some of the weaknesses or limitations of the study may be presented in this section, as well as the proposed next research steps. The authors may compare their results with other studies that asked a similar research question, which can give you some insight into how this study fits into the big picture. Figure 8: The conclusion is where all of the pieces of the puzzle get put together, and the researchers interpret their data. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 177 LESSON READINGS Works cited At the end of a research article you will find a long list of other studies in the works cited, or bibliography. These are the studies that have either led up to the BIG research Question of this study, or contain the Methods used in this study. In general, most of the works cited should be recently published (within five years from the date the current study was published), showing that the researchers have kept up with what other scientists have done to advance understanding of the field. Wo r k b o o k Lesson 4.5 ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 178 STUDENT RESPONSES We discussed in Lesson 4.4 how study results are misinterpreted in the media. Now that you are more familiar with the structure of a research article, list some ideas why these misinterpretations might occur. _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ ____________________________________________________________________________________________________ Remember to identify your sources _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ Wo r k b o o k Lesson 4.5 _____________________________________________________________________________________________________ ___________________________________________________________________________________________ 179 Unit 5: Where are we heading? Unit 1: What’s in your food? Unit 2: How does your body use food? Unit 5: Introduction Unit 3: What is metabolic disease? Unit 4: How do I identify ‘good’ and ‘bad’ food? Unit 5: How does this knowledge apply to me? ______________________________________ In the last four units we have learned about the composition of food, digestion and metabolism, metabolic diseases, and how to evaluate nutritional research. This leaves us with the question of how to apply this information to our lives. 180 LESSON 5.1 WORKBOOK How can you use what you know to evaluate claims? (1) In this lesson we will use the knowledge gleaned from the previous four units to create a toolbox for evaluating nutritional claims and dietary recommendations. Evaluating nutritional claims Wo r k b o o k Lesson 5.1 So far in this module we have learned a lot about nutrition: from how food is produced to how our bodies use and respond to food after we eat it. All of the information that we have learned is based on scientific findings. In Unit 4 we learned about the characteristics and challenges of conducting a nutritional study. Study results are often misinterpreted when being shared with the public, which can lead to nutritional claims or dietary recommendations that are not based on scientific findings. Using the information that we have learned over this module, we can form specific criteria to thoroughly evaluate nutrition claims. Figure 1: The same scientific results should be found multiple times by several scientists to confirm that they are reproducible. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 181 LESSON READINGS Forming a rubric for evaluating a nutritional claim Figure 2: Nutritional claims or dietary recommendations are commonly found in magazines. There are many types of nutritional claims that you may come across when you are watching television or reading a newspaper or magazine. Some of these may be scientifically backed, some may be accidental misinterpretations of the science, and some may be intentionally misleading! What you learned in the four previous Units can be used to question the validity of the claim. ■■ Unit 1: What’s in your food? – What nutrient or food is the claim about? Is it a micronutrient or a macronutrient? Is the claim about a purified component of a food (like a supplement), or is it about an entire dietary pattern rich in some nutrients and lacking others? ■■ Unit 2: How does your body use food? – How is the nutrient or food of interest digested? How is it metabolized? Is the claim consistent with what we know about digestion, absorption and metabolism? ■■ Unit 3: What is metabolic disease? – How does our body as a whole respond to this food or nutrient? Do we feel full or hungry after eating it? Is there a link between the food or nutrient to obesity and metabolic diseases? Will this lifestyle change alter metabolic rate? ■■ Unit 4: How do I identify ‘good’ and ‘bad’ foods? – Is the claim based on a scientific study? If so, what type of study was it? What kind of conclusions can you make from that type of study? Were all of the confounding variables accounted for? Was there any type of bias? Use the QMDC model to evaluate the study. Wo r k b o o k Lesson 5.1 Figure 3: If it’s an observational study your conclusions are limited. An example of evaluating a dietary claim You have learned about the Mediterranean diet in previous units. The typical Mediterranean diet is one that is high in fish, beans, nuts, fruits, vegetables and olive oil, and it is a diet that is lauded for its health ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 182 LESSON READINGS benefits. This diet is commonly advertised (see Figure 4 below for an example) as being one of the best diets for weight loss, longevity and overall health, but is it healthy for everyone and how were these conclusions derived? Does the science back them up? Figure 4: A news article describes the benefits of an Ancient Greek diet. Are these claims scientifically based? Source: WTOP News After reading the original research article we can determine more about the study referred to in the article and how it was performed. The title of the research article published in The American Journal of Clinical Nutrition is Cretan Mediterranean diet for prevention of coronary heart disease, from which we can already discern that the study was conducted in regards to preventing a type of heart disease. Take a moment to read through the abstract of the article on the next page. Wo r k b o o k Lesson 5.1 ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 183 LESSON READINGS ABSTRACT: As a result of the Seven Countries Study, the Mediterranean diet has been popularized as a healthy diet. Nevertheless, it has not replaced the prudent diet commonly prescribed to coronary patients. Recently, we completed a secondary, randomized, prospective prevention trial in 605 patients recovering from myocardial infarction in which we compared an adaptation of Cretan Mediterranean diet with the usual prescribed diet. After a mean follow-up period of 27 mo, recurrent myocardial infarction, all cardiovascular events, and cardiac and total death were significantly decreased by > 70% in the group consuming the Mediterranean diet. These protective effects were not related to serum concentrations of total, low-density-lipoprotein (LDL), or high-density-lipoprotein (HDL) cholesterol. In contrast, protective effects were related to changes observed in plasma fatty acids: an increase in n-3 fatty acids and oleic acid and a decrease in linoleic acid that resulted from higher intakes of linolenic and oleic acids, but lower intakes of saturated fatty acids and linoleic acid. In addition, higher plasma concentrations of antioxidant vitamins C and E were observed. We conclude that a Cretan Mediterranean diet adapted to a Western population protected against coronary heart disease much more efficiently than did the prudent diet. Thus it appears that the favorable life expectancy of the Cretans could be largely due to their diet. Am J Clin Nutr 1995; 61(suppl):1360S-7S. Figure 5: Abstract of Cretan Mediterranean diet for prevention of coronary heart disease. For clarification, note that linolenic acid is an omega-3 (n-3) fatty acid, and linoleic is an omega-6 fatty acid. Both types of omega fatty acids are essential, but the Mediterranean diet is especially high in omega-3 fatty acids whereas the Westernized diet is high in omega-6 fatty acid. Oleic acid is the monounsaturated fatty acid that is found in olive oil. Wo r k b o o k Lesson 5.1 Before we can begin to go through our rubric to evaluate the claim that the Ancient Greek diet is the healthiest, we first need to define some terms and determine how the study was conducted. The abstract begins by referring to another study, the Seven Countries Study, which was the original published research that brought the Mediterranean diet into the public eye. The researchers of the current study are focusing on a specific type of Mediterranean diet that is consumed by people living on the Greek island of Crete, a diet called the Cretan Mediterranean diet. The participants of this study were people living in a Westernized culture that were recovering from a myocardial infarction (heart attack), and the study was conducted in France. Study participants were randomly assigned to either receive dietary counseling about the Cretan Mediterranean diet (the experimental group), or to receive the dietary recommendations that are standard after hospitalization for a heart attack (the control group). ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 184 LESSON READINGS The Cretan Mediterranean diet that was recommended to the experimental group consisted of “The Six Dietary Commandments”: 1. More bread. 2. More vegetables and legumes. 3. More fish. 4. Less meat (beef, lamb, pork) and replaced by poultry. 5. No day without fruit. 6. Replaced butter and cream with a special oil-based margarine that has similar fatty acid types to olive oil. Figure 6: Crete (in red) is a Greek island south of the mainland. The researchers end goal was to determine whether the Cretan Mediterranean diet could prevent another heart attack, cardiovascular event or death. They used measurements of LDL, HDL, and blood concentrations of the essential fatty acids to determine if the two diets resulted differences in the participants. Using the rubric to evaluate the Ancient Greek diet Now let's walk through the rubric we formed to evaluate the nutritional claim that the Ancient Greek diet is the healthiest diet. ■■ Unit 1: What’s in your food? – This claim is regarding a total diet, namely the Ancient Greek, or Cretan Mediterranean diet. The diet in the news article is “rich in fish, vegetables, fruits and, above all olive oil”. Wo r k b o o k Lesson 5.1 Figure 7: The Cretan Mediterranean diet is high in bread, fruits, vegetables and fish. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 185 LESSON READINGS ■■ Unit 2: How does your body use food? – The Mediterranean diet that is described by the news article would be high in omega-3 fatty acids from the fish, monounsaturated fatty acids from the olive oil, as well as fiber, and micronutrients from the fruits and vegetables. Both omega-3 and monounsaturated fatty acids are important for building cell membranes and maintaining normal cellular functions. Also, because the saturated fat intake is low, the HDL to LDL ratio in the blood may increase, which we know is correlated with a low risk of heart disease. Additionally, soluble fiber from the vegetables and fruits can absorb bile from the intestines so that it is excreted in the feces. Remember that bile is made of cholesterol; therefore eating soluble fiber can decrease your body’s total cholesterol levels. ■■ Unit 3: What is metabolic disease? – Eating a diet rich in fat, protein and fiber makes us feel full for a longer period of time than eating a highly processed diet rich in simple carbohydrates. The Mediterranean diet is high in fat, protein and fiber, so an overall decrease in calories consumed is possible if the diet is strictly adhered to. However, the dietary recommendations for the experimental group do not limit calorie intake, so weight loss may not be expected. This diet is also low in sweet foods, so the reward pathway will not be activated as fully as it would when we eat our favorite sweet and fatty foods. Food cravings for sweet foods may be present while eating this diet, perhaps leading to more snacking and increased calorie consumption. ■■ Unit 4: How do I identify ‘good’ and ‘bad’ foods? – Now let's use the QMDC method to walk through the published scientific article that is referred to in the news piece. The BIG Question was whether a Cretan Mediterranean diet could prevent coronary heart disease better than a standard diet prescribed to patients who have had a heart attack. The Method used was a randomized controlled study, though it was not double-blinded because the participants knew what type of diet they were following. Because this was an interventional study, causative results and conclusions can be made, but be careful! We must determine if all types of biases were accounted for. Is there selection bias? Information bias? A confounding variable? Notably, this study had participants with a history of heart disease, which may impact the types of conclusions you make. Wo r k b o o k Lesson 5.1 Observational Correlation Interventional Causation Figure 8: The type of study determines the extent of the conclusions you could make. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 186 LESSON READINGS The Data are shown in tables and figures throughout the scientific article, two of which are presented below. The first table shows the comparison of nutrients eaten in the control and experimental groups. Nutrients that had the largest differences between groups are shaded in red. What conclusions can you make using the table? Were the two diets rich in different nutrients? Is the difference in diets meaningful or just measurable? Intake of nutrients in the experimental and control groups a6er 1-‐4 years Control Group Experimental Group 2152 ± 10038 1941 ± 7920 Protein 16.6 ± 0.3 17.0 ± 0.3 Total lipids 33.1 ± 0.6 30.6 ± 0.5 Saturated fat 11.8 ± 0.3 8.3 ± 0.2 Monounsaturated fat 10.4 ± 0.3 12.9 ± 0.3 Linoleic Acid 5.4 ± 0.2 3.6 ± 0.1 Linolenic Acid 0.28 ± 0.02 0.83 ± 0.03 Vitamin A (ug) 548 ± 111 279 ± 72 Vitamin C (mg) 101 ± 4 118 ± 4 Vitamin D (ug) 2.8 ± 0.6 1.6 ± 0.2 Vitamin E (mg) 13.6 ± 0.5 12.1 ± 0.3 Cholesterol (mg) 320 ±14 217 ± 11 Total Energy (kcal) Percent of energy (%) Figure 9: Table adapted from Cretan Mediterranean diet for prevention of coronary heart disease showing the differences in macro and micronutrients between the two diets. Nutrients shaded in red are significantly different in the two groups. Wo r k b o o k Lesson 5.1 The graph in Figure 10 (see next page) shows the number of study participants in both the experimental and control groups that did not have an 'event', which is either a heart attack, death from heart attack, stroke or a blood clot from atherosclerosis. The Data shows that the experimental group had far fewer 'events' than the control group. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 187 LESSON READINGS From this data would you agree that the Ancient Greek diet is the healthiest diet for everyone? If we were to only use the study discussed here as evidence, would it be difficult to argue that a healthy person can benefit from following the Ancient Greek diet, or does the conclusion seem solid? Wo r k b o o k Lesson 5.1 Population without event! Finally, using the Data we can make some Conclusions. The experimental diet presented in this scientific article did seem to contain different macro and micronutrients than the control diet. As mentioned in the abstract, the experimental group had high omega-3 fatty acids and lower omega-6 fatty acids in their blood compared to the control group. Overall, the experimental group had less cardiovascular events, and the Cretan Mediterranean diet protects against heart disease more efficiently than the control diet in a population that has already suffered a heart attack. Experimental! Control! Years after randomization! Figure 10: Figure from Cretan Mediterranean diet for prevention of coronary heart disease illustrating the proportion of each population that has not had a cardiovascular event. ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ ________________________________ 188 STUDENT RESPONSES List three alternative explanations to explain the results in figure 10. To form your answer, consider who the study participants were, what type of study was conducted, what the treatment and control groups were, how long the study was conducted, and what measures were made. _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ Remember to identify your sources ____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ _____________________________________________________________________________________________________ Wo r k b o o k Lesson 5.1 _____________________________________________________________________________________________________ ___________________________________________________________________________________________ 189 LESSON 5.2 WORKBOOK How can you use what you know to evaluate claims? (2) GREAT DISEASES RESEARCH GUIDE WEBSITE ResearchGuides.Library.Tufs.Edu/ GreatDiseases How to Search (And do it Well) Learning Where to Search The Value of Vocabulary Now that we have a rubric we can use to evaluate nutritional claims and dietary recommendations, where to we find trusted information? In this lesson we will discuss where to look for valuable resources of scientific findings and how to search for scientific articles. The Science of Searching: Creating Search Formulas The Art of Searching: Practice Makes Perfect Is it CRAAP? Assess Your Findings! To access the Research Guide, click on the link — Great Diseases Research Guide — or visit the multimedia page for this unit on the student site. Wo r k b o o k Lesson 5.2 Tips and tricks for researching your topic After you have chosen a topic to investigate, the next step is to research that topic using reliable sources of scientifically based information. If you were to type your topic into a Google search, chances are you are going to end up with unreliable results, and a lot of them! There some basic tips and tricks that will help you find and sort through credible scientific resources online. In general, there are three parts of this process: 1. Finding the correct vocabulary to use for the search. 2. Creating search formulas using the vocabulary that yield relevant results. 3. Evaluating your results so that you only spend time reading the ones that are most helpful to you. To get the most out of this workbook lesson you should also follow along on the Great Diseases Research Guide website (See left sidebar for link and url). On the website you will find links to databases where you can search for information regarding your topic, as well as tutorials about how to best utilize these resources. Go to the website now and watch the introductory video "Librarians: Your Partners in Research!". 190 LESSON READINGS Using the ‘right’ vocabulary Once you have opened up the Research Guide website you will find a link called “The Value of Vocabulary”. Click on the 'Value of Vocabulary' link, read through the text and watch the video. After reading this section, try to summarize the main points below. Why is having the right vocabulary so important when you search for information about your topic? What tools are available to help you find all of the synonyms associated with your topic? Write your notes below. ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ Searching efficiently Wo r k b o o k Lesson 5.2 Figure 1: Computers are tools to find information, but you need to tell them what to look for! Now go to the sections of the Research Guide website called "The Science of Searching: Creating Search Formulas" and "The Art of Searching: Practice Makes Perfect". Read through the text and watch the video. You will learn about techniques that will make searching for specific content online easier. Take notes about these sections on the next page. What are operators, and how are they useful? You may find it helpful to write examples of the operators. Be sure to read the warning about using operators, as not all scientific databases allow the use of operators in their search function. 191 LESSON READINGS ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ Evaluating your search results Wo r k b o o k Lesson 5.2 On the Research Guide website homepage click on the link called “Is it CRAAP? Assess your Findings!”. Evaluating your search results is an important step in researching your topic. If you try to read all of the scientific articles available it may take years! Instead, use the checklist presented in this section to determine if a scientific article is worth your time. Figure 2: It is important to use credible sources of information when researching a topic on the internet. 192 LESSON READINGS The CRAAP test will help you determine if an article or website’s claim is worth scrutinizing. For example, is the article or website: • C urrent? • R elevant? • A uthoritative? • A ccurate? • P urposeful? After reading through the text online and looking at the CRAAP checklist, summarize this section below. How is the CRAAP test useful? ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ Online tutorial: Searching for scientific resources Wo r k b o o k Lesson 5.2 After you have reviewed the information on the homepage of the Research Guide website click on the Metabolic Disease tab at the top. Here you will find a list of websites where you can search for scientific articles that are openly available to you. You will also see a link to an online tutorial called “Searching for Scientific Resources”. In this tutorial you will be walked through an example of a topic search. You will get to practice the three steps we have discussed here: vocabulary, searching efficiently, and evaluating your results. ■■ Great Diseases Research Guide site: Metabolic Diseases Tutorial 193 LESSON READINGS A review of your toolbox Throughout this course you have learned many useful skills that will help you navigate scientific literature as you research your topic. Those tools are summarized below: ■■ QMDC: Each article you read will contain a BIG Question, Methods, Data and a Conclusion. Also remember to use QMDC when you look at figures in an article, since each figure is answering a Question, was created from a series of Methods to represent Data and a Conclusion. Refer to Lesson 4.5 to review QMDC in more detail. Figure 3: You have learned many tools and skills to help you research your topic! ■■ Review of Methods: You have learned about the different types of observational and interventional studies. Remember that the type of methods used determines the types of conclusions that can be made. To review methods and study designs refer to Lesson 4.3. Also recall that correlation and causation are two very different types of results! Make sure that you can make this distinction as you read through scientific articles. ■■ CRAAP Test: To determine whether the article you have found is worth reading and evaluating put it through the CRAAP test. The CRAAP checklist is found online on the Research Guide website. ■■ Project Rubric: In the beginning of Unit 5 you were asked to create a rubric to evaluate a nutritional claim. This rubric was created from all of the content that we have learned over the Metabolic Disease module. Remember to use the rubric and scientific articles to evaluate your topic. Wo r k b o o k Lesson 5.2 194 LESSON 5.3 WORKBOOK Researching Your Project Topic Now it's your turn to try your hand at evaluating a nutrition or dietary claim! Prepare a presentation using one of the topics below. Be sure to use the rubric created in Unit 5 to evaluate the claim. Use the QMDC and CRAAP methods as you read through scientific resources regarding the topic. For more information about searching for credible scientific resources, visit the following research guide via this unit on the student site or clicking the link below: ■■ Great Diseases Guide to Searching for Claims Diets Topic Paleo Diet Claim Explanation What is this related to? Eating a diet similar to our ancestors leads to weight loss. A nutritional plan based on the presumed ancient diet of wild plants and Obesity animals. This diet is high in grass-fed meats, fruits and vegetables, and low in processed foods, carbohydrates and dairy. South Beach Preventing spikes and drops in insulin A diet designed by cardiologist Arthur Agatston and dietician Marie Almon Obesity prevents weight gain. originally to prevent heart disease. This diet focuses on low glycemic index Diet foods and consists of whole grains, fruits, vegetables and lean meats. Wo r k b o o k Lesson 5.3 Blood Type Diet People with different blood types need Popularized by the book Eat Right 4 Your Type, the blood type diet is actuto follow different diets to lose weight. ally a series of types of diets that vary based on blood type. Obesity 195 PROJECT TOPICS Topic Vegetarian Diet Gluten Free Diet Diets cont. Claim Explanation What is this related to? Eliminating meat from the diet increases overall longevity. A diet high in fruits, vegetables and whole grains is high in fiber, vitamins, minerals and typically low in fat and calories. Obesity; overall health Gluten sensitivity causes fatigue, Gluten is a protein found in wheat, rye and barley. Celiac disease is a headaches, abdominal discomfort and diagnosable disease that affects about 10% of the population. Gluten other symptoms. sensitivity is harder to diagnose, though many people feel a relief from symptoms by removing gluten from their diet. Digestion disorders; overall health Nutrition through the lifecycle Topic Claim Folic acid in Reduction in neural tube birth pregnancy defects in offspring. Wo r k b o o k Lesson 5.3 Explanation What is this related to? Women who take a folic acid supplement during pregnancy have a lower chance of having a baby with a spinal cord malformation, called spina bifida. Methylmercury in seafood can build to toxic levels in women who are pregnant. Neural tube birth defects Eating nitrates leads to cancer in offspring. Sodium nitrate and sodium nitrite are preservatives used in deli meats. They are converted into nitrosamine in the body, a carcinogen. Fetuses may be more susceptible to nitrosamines. Cancer Eating fish during pregnancy Nitrates during pregnancy Probiotics in infant formula Babies exposed to methylmercury in the womb can suffer from brain damage. Probiotics prevent infection and inflammation in infants Breastfed infants will be exposed to beneficial microorganisms from Infectious diseases their mothers. Probiotics in formula provide similar exposure even when the infant is not breastfed. Vitamin D supplements for infants Calcium supplements in teenagers Breastmilk does not contain enough vitamin D for infants, so supplementation is necessary Consuming extra calcium during adolescence reduces osteoporosis later Longterm caffeine consumption reduces the cognitive declines associated with aging Babies in northern climates or those not regularly exposed to skin cannot make enough vitamin D, and breastmilk can be low in vitamin D if the mother is deficient. Up to 90% of the peak bone mass is acquired by age 18 in girls and age 20 in boys, so adolescence is the best time to invest in calcium storage. Habitual users of caffeine have a lower risk of Alzheimer's disease, Parkinson's disease and cognitive decline during aging. Caffeine may increase concentrations of neurotransmitters in the brain. Caffeine and aging Nervous system defects Rickets and possibly muscle development Osteoporosis Neurological disorders 196 PROJECT TOPICS Topic Protein powder and muscle building Creatine and muscle building Weight loss supplements Vitamin B12 in energy drinks Non-skeletal benefits of Vitamin D Claim Explanation Consuming extra protein will increase muscle growth New muscles are built in response to increase need for strength. An Muscular development adequate supply of amino acids is required for new muscle growth, so some believe consuming extra amino acids will allow muscles to grow quicker. What is this related to? Taking creatine supplements helps Creatine is used in the muscles to supply extra energy when muscle gain needed by increasing the formation of ATP. Muscular development Taking weight loss supplements will expedite weight loss Weight loss supplements commonly contain caffeine for energy, fiber to keep you feeling full, and "extracts" that promise to burn fat. Obesity Consuming extra vitamin B12 increases energy Vitamin B12 is needed for proper function of blood cells, brain and nervous system. Some food producers claim that vitamin B12 increases energy and athletic performance. Energy and cognition Vitamin D supplements promotes overall health and reduces infections Blood levels of vitamin D are lowered in people with heart disease, some cancers, an infectious disease and other illnesses relative to health people. Infectious diseases; overall health Omega 3 fatty acids supplements and heart disease Taking fish oil supplements lowers your risk for heart disease Fish oil is high in omega 3 fatty acids, which may lower blood lipids including LDL. Heart disease Vitamin C and prevention of colds Caffeine and athletic endurance Taking Vitamin C supplements reduces the risk of getting a cold Vitamin C is an anti-oxidant and has been linked to preventing colds Infectious diseases for decades. Consuming caffeine increases athletic endurance Caffeine is a stimulant and provides energy, which may be able to increase an athelete's performance. Athletic performance It may seem like a daily dose of vitamins and minerals can only be beneficial, but several studies have recently shown that daily multivitamin use either has no benefits, or is actually linked to death at an earlier age than non-vitamin users. Infectious diseases; overall health Multivitamins Taking a daily multivitamin and overall prevents illness and increases health overall longevity Wo r k b o o k Lesson 5.3 Dietary Supplements 197 PROJECT TOPICS Topic Food coloring Caramel coloring Artificial sweeteners MSG BPA Wo r k b o o k Lesson 5.3 Food Additives Claim Explanation What is this related to? Consumption of artificial food coloring increases hyperactivity in children Consumption of caramel coloring increases risk of cancer Artificial food colorings are synthesized chemicals added to processed foods and may have negative health effects. Neurological disorders Caramel coloring is an artificial color used in sodas and some baked Cancer goods. It contains methylimidazole, a carcinogen. Consumption of some artificial Aspartame and sucralose are both artificial sweeteners that have sweeterns increases risk of cancer been blamed for causing cancer. Cancer MSG is linked to migraines, nausea and weakness. BPA causes developmental and behaivoral disorders Neurological disorders Monosodium glutamate is a flavor enhancer that may may alter chemical signalling in the brain. BPA is a synthetic plastic that when consumed may alter hormonal signaling that harms the brain and the reproductive system. Neurological disorders; Reproductive disorders 198 The Great Diseases Project Department of Developmental, Molecular and Chemical Biology 150 Harrison Ave., Boston, MA 02111