Download kbook or W METABOLIC DISEASE

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
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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.
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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.
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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.
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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
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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.
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10
STUDENT RESPONSES
Give a brief argument both for and against the statement “a candy bar should be considered food”.
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Wo r k b o o k
Lesson 1.1
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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Wo r k b o o k
Lesson 1.2
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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.
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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.
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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.
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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.
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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.
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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!
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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?
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Wo r k b o o k
Lesson 1.3
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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.
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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.
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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.
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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.
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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
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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.
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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?
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Lesson 1.4
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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
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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?
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Wo r k b o o k
Lesson 1.5-6
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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.
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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.
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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?
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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.
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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.
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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
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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.
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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
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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.
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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.
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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?
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Wo r k b o o k
Lesson 2.1
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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!
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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.
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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.
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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.
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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.
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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.
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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.
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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
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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?
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Wo r k b o o k
Lesson 2.2
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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.
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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.
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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.
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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.
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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.
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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.
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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?
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Wo r k b o o k
Lesson 2.3
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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?
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Wo r k b o o k
Lesson 2.4
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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.
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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.
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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.
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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.
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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.
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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?
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Lesson 2.5
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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
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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.
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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.
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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.
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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.
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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.
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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).
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Lesson 3.1
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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
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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.
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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.
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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.
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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.
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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?
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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.
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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.
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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.
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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.
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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.
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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?
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Wo r k b o o k
Lesson 3.3
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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.
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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.
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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.
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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.
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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.
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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?
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Lesson 3.4
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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.
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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.
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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.
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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.
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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.
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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.
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Lesson 3.5
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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Wo r k b o o k
Lesson 3.6
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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.
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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.
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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.
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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.
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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.
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What are the pros and cons of conducting nutritional studies in humans vs. mice?
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Lesson 4.1-2
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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.
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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.
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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.
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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.
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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.
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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.
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■■ 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.
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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.
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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?
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Lesson 4.3
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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.
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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.
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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.
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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.
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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.
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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.)
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Lesson 4.4
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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?
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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:
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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,
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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!
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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.
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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
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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.
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Wo r k b o o k
Lesson 4.5
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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?
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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.
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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.
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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
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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
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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).
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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.
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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.
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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.
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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.
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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.
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Wo r k b o o k
Lesson 5.1
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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!".
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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.
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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.
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LESSON READINGS
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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?
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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