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Chapter 4: Carbohydrates: Sugar, Starch, Glycogen and Fiber Carbohydrates (CHO)—composed of carbon, hydrogen and oxygen; two types, simple and complex. Simple carbohydrates ◦ Sugar is a simple CHO—CHO composed of single and linked sugars (mono and disaccharides) Complex carbohydrates ◦ Starch and fiber The three single sugars (monosaccharides) are ◦ Glucose ◦ Fructose ◦ Galactose The three double sugars (disaccharides) ◦ Lactose It is made of glucose linked to galactose ◦ Maltose It is made of two glucose units ◦ Sucrose It is made of glucose linked to fructose Starch—long chains of glucose units found in plants. Glycogen-the storage form of CHO found in animals. Soluble fibers dissolve in water • • • • • Form gels (are viscous) Easily digested by bacteria in the human colon Found in barley, legumes, fruits, oats, vegetables Are associated with a lower risk of chronic disease Add a pleasing consistency to foods Insoluble fibers do not dissolve in water • Are less easily fermented • The outer layers of whole grains, the strings of celery, etc. contain insoluble fibers such as cellulose and hemicellulose • These fibers retain their structure and texture even after hours of cooking • They aid the digestive system and ease elimination Human digestive enzymes cannot break the bonds between the sugar units of starch ◦ Thus, most fibers pass through the human body without providing energy Bacteria within the human large intestine can digest fibers to varying degrees by fermenting them ◦ This produces gas in many people DRI recommendations WHO recommendation Recommendations and Intakes ◦ 2000 calorie diet with 225-325 grams of carbohydrate per day ◦ 2000 calorie diet with 275-375 grams of carbohydrate ◦ DRI recommendations for fiber: Men, age 19-50: 38 g/day Men, age 51+: 30 g/day Women age 19-50: 25 g/day Women age 51+: 21 g/day Children, age + 5 grams (ADA recommendation) The ADA recommends 20 to 35 grams of total fiber per day This is about 2x higher than the average intake The DRI committee recommends that 45% - 65% of daily calories come from carbohydrates Fats are not normally used as fuel by the brain and central nervous system ◦ Glucose is the primary energy source for nerve cells Gram for gram carbohydrates contain fewer calories (4) than do dietary fats (9) Converting glucose into fat is metabolically costly Benefits of fiber include: ◦ Promotion of normal blood cholesterol concentrations ◦ Modulation of blood glucose concentrations ◦ Maintenance of healthy bowel functions ◦ Help in the maintenance of a healthy body weight ◦ Help to avoid insulin spiking ◦ Increase satiety ◦ ….and more Lower Cholesterol and Heart Disease Risk ◦ Diets rich in complex carbohydrates may protect against heart disease Such diets are usually: low in saturated fat, trans fat, and cholesterol High in fibers, vegetable proteins, and phytochemicals How fiber reduces cholesterol levels •Foods rich in viscous fibers lower blood cholesterol by binding with cholesterol-containing bile and carrying it out with the feces •Bile is needed for digestion, so the liver responds to its loss by drawing on the body’s cholesterol to make more Blood Glucose Control ◦ Viscous fibers trap nutrients and delay transit through the digestive tract As a result glucose absorption slows and this helps maintain steady levels of blood glucose and insulin Large fluctuations in blood glucose and insulin are thought to be associated with the onset of the most common form of diabetes In people with diabetes, high-fiber foods play a role in modulating blood glucose and insulin levels ◦ Lowering the likelihood of medical complications Healthy Weight Management ◦ Foods rich in complex carbohydrates tend to be low in fats and added sugars They, therefore, promote weight loss by providing less energy Fibers also create feelings of fullness and delay hunger because they swell as they absorb water ◦ Buying such pure fiber compounds is neither necessary nor advisable Maintenance of Digestive Tract Health ◦ Fiber, along with fluid intake, play a role in maintaining proper colon function Fibers such as cellulose enlarge and soften stools Speeding their passage through the intestine and making for easier elimination These fibers help alleviate or prevent constipation Constipation is difficult, incomplete, or infrequent bowel movements ◦ Associated with discomfort in passing dry, hardened feces ◦ Large, soft stools ease the task of elimination for the rectal muscles Making it less likely that the rectal veins will swell (hemorrhoids) Fiber prevents compaction of intestinal contents ◦ Such compaction could obstruct the appendix and permit bacteria to invade and infect it (appendicitis) Fiber stimulates the GI tract muscles so they retain their strength and resist bulging out into pouches (diverticula) ◦ Diverticulitis is the inflammation of diverticula Diverticulosis/ Diverticulitis diverticula colon High-fiber diets lower the rates of colon cancer ◦ Nutrient & phytochemical content of fiber-rich foods ◦ Fibers dilutes & helps remove of cancer-causing agents from the colon Lowering the pH of intestinal contents ◦ Contributing to the destruction of cancer cells and slowing cancer cell replication ◦ To obtain glucose from food the digestive system must first break down carbohydrates in the food into monosaccharides that can be absorbed Starts in the Mouth: Starch ◦ Starch digestion begins in the mouth An enzyme in saliva splits starch into maltose This enzyme continues to act on starch while it remains in the stomach’s upper storage area In the stomach, CHO mixes with acid and salivary enzymes are deactivated Starch digestion resumes in the small intestine ◦ Where a starch-splitting enzyme produced by the pancreas acts Digestible carbohydrates are ultimately split into monosaccharides before they are absorbed Disaccharides and small polysaccharides are split by enzymes attached to the cells lining the small intestine Digestion of Carbohydrates esophagus liver pancreas stomach small intestine large intestine (colon) 1 Fiber, starch, monosaccharides, and disaccharides enter the stomach and pass into the small intestine. Some of the starch is partially broken down by an enzyme from the salivary glands before it reaches the small intestine. esophagus liver pancreas stomach small intestine large intestine (colon) 2 An enzyme from the pancreas digests most of the starch to disaccharides. intestine wall cells capillary esophagus liver pancreas stomach small intestine large intestine (colon) intestine wall cells capillary 3 Enzymes on the surface of intestinal wall cells split disaccharides to monosaccharides. esophagus liver pancreas stomach small intestine large intestine (colon) intestine wall cells capillary 4 Monosaccharides enter capillaries, then are delivered to the liver via the portal vein. esophagus liver pancreas stomach small intestine large intestine (colon) intestine wall cells capillary 5 The liver converts galactose and fructose to glucose. As blood glucose rises, the pancreas releases insulin ◦ Insulin signals the body’s tissues to take up glucose 2/3 of total glycogen is stored in & used by muscle A small emergency store is found in the brain The remainder is stored in the liver, which makes it available to the body as blood glucose When blood glucose concentration drops the pancreas produces glucagon ◦ Enzymes in the liver break down glycogen releasing it into the blood as glucose Epinephrine also breaks down liver glycogen as part of the body’s defense mechanism in times of danger ◦ To a person living long ago, this internal source of quick energy was indispensable to a life filled with physical peril ◦ This quick-energy response to stress also works to our advantage today To meet emergencies, we are advised to eat and store carbohydrates at regularly timed meals Diabetes mellitus ◦ A disease characterized by high blood glucose levels and inadequate or ineffective insulin The prevalence of diabetes is increasing ◦ Leading cause of blindness in the US Additional complications include: ◦ ◦ ◦ ◦ ◦ ◦ Amputations Complications in pregnancy Heart disease Kidney disease Premature death Increased risk of death from flu or pneumonia Type 1 Diabetes ◦ Little or no pancreatic secretion of insulin ◦ Often diagnosed in childhood ◦ Less common (up to 20% of cases) Most common chronic disease among children and young adults Type 1 diabetes is the result of a person’s immune system attacking the insulin-making cells of the pancreas ◦ An immune system attack on the pancreas may be provoked by Genetics, viral infection and other diseases, toxins, allergens, disordered immune system Type 2 Diabetes ◦ ◦ ◦ ◦ Pancreas makes sufficient insulin Body’s cells resist insulin’s action Often diagnosed in adulthood Incidence has increased by over 60% since 1991 Characterized by insulin resistance ◦ A condition in which insulin is less then effective in moving glucose from the bloodstream into the cells ◦ As blood glucose rises, so does blood insulin Eventually, the pancreas is unable to make insulin With age, people may require insulin to supplement their own supply Type 2 Diabetes and the Genes ◦ Genetic component to Type 2 susceptibility Genes are not destiny Genetic factors may increase a person’s risk by ≈30% Diet and exercise play a major role Prevention is likely when individuals control lifestyle ◦ Men and women can reduce their risk if they: Maintain a healthy body weight Consume a diet high in vegetables, fruit, fish, poultry, and whole grains Exercise regularly Restrict alcohol Don’t smoke Half of those with diabetes are unaware of their condition ◦ And therefore fail to take action to prevent its damage ◦ Early stages often present few or no warning signs ◦ Recommendations call for everyone over 45 years old (40 in Canada) and younger people with risk factors, such as obesity, to be tested regularly Warning Signs of Diabetes Type 1 and Type 2 are the most common forms of diabetes ◦ Both are disorders of blood glucose regulation Comparison of Type 1 & Type 2 Diabetes Managing Diabetes ◦ Optimal diet: Is adequate in nutrients Provides the recommended amount of fiber Is moderate in added sugars Provides a controlled amount of total carbohydrates Is low in saturated fat and may provide some monounsaturated fat Is adequate but not too high in protein The Glycemic Response ◦ The glycemic index (GI) is a measure of the ability of a food to elevate blood glucose and insulin levels Scores are compared with a standard, usually white bread or glucose A food’s score depends on several factors For example, ice cream, a high-sugar food, ranks lower than baked potatoes, a high-starch food Glycemic Index The GI of foods is affected by: •Individual differences among people •Ripeness of fruits/vegetables •Other foods consumed at the same time Who might find this information helpful for making dietary choices? •People with Diabetes •Those dieting •Athletes Hypoglycemia ◦ Blood glucose concentrations below normal Symptoms include: ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ Fatigue & Weakness Dizziness & Trembling Irritability Rapid heartbeat Anxiety Sweating Hunger Headaches Confusion Impairment of intellectual tasks