The Carbohydrates: Sugars, Starches, and Fibers Chapter 4 © 2016 Cengage Learning. All Rights Reserved. © 2016 Cengage Learning. All Rights Reserved. Introduction • Brain • Glucose • Muscles • Glucose • Glycogen • Fat • Sources of carbohydrates • “Fattening” – mistaken thinking © 2016 Cengage Learning. All Rights Reserved. Chemist’s View of Carbohydrates • Carbohydrate family • Atoms and chemical bonds • Monosaccharides • Simple carbohydrates • Glucose, fructose, galactose • Disaccharides • Maltose, sucrose, lactose • Polysaccharides • Complex carbohydrates © 2016 Cengage Learning. All Rights Reserved. Atoms and Their Bonds © 2016 Cengage Learning. All Rights Reserved. Monosaccharides • Same numbers and kinds of atoms • Differing sweetness • Glucose – blood sugar • Essential energy source • Part of every disaccharide • Fructose • Sweetest of the sugars • Galactose • Only in a few foods © 2016 Cengage Learning. All Rights Reserved. Chemical Structure of Glucose • • • On paper, the structure of glucose has to be drawn flat, as it is in the first diagram, but in nature the five carbons and oxygen are roughly in a plane. The atoms attached to the ring carbons extend above and below the plane. In the second diagram, the lines representing some of the bonds and the carbons at the corners are not shown. In the third diagram, the single hydrogens are not shown, but lines still extend upward or downward from the ring to show where they belong. © 2016 Cengage Learning. All Rights Reserved. Chemical Structure of the Monosaccharides © 2016 Cengage Learning. All Rights Reserved. Disaccharides • Pairs of three monosaccharides • Maltose – two glucose units • Sucrose – glucose and fructose • Lactose – galactose and glucose • Condensation • Links two monosaccharides together • Hydrolysis • Breaks a disaccharide in two © 2016 Cengage Learning. All Rights Reserved. Hydrolysis of a Disaccharide © 2016 Cengage Learning. All Rights Reserved. Polysaccharides • Glycogen • Storage form of energy in the body • Glucose molecules linked together in highly branched chains • Starches • Storage form of energy in in plants • Glucose molecules linked together in branched or unbranched chains © 2016 Cengage Learning. All Rights Reserved. Glycogen and Starch Compared © 2016 Cengage Learning. All Rights Reserved. Glycogen A glycogen molecule contains hundreds of glucose units in highly branched chains. Each new glycogen molecule needs a special protein (shown here in red) for the attachment of the first glucose. Starch (amylopectin) Starch (amylose) A starch molecule contains hundreds of glucose molecules in either occasionally branched chains (amylopectin) or unbranched chains (amylose). Stepped Art – Glycogen and Starch Compared Dietary Fibers • • • • • • • Structural parts of plants Differ from starches Soluble fibers – benefits Insoluble fibers – benefits Functional fibers Resistant starches Phytic acid © 2016 Cengage Learning. All Rights Reserved. The Bonds of Starch and Cellulose Compared © 2016 Cengage Learning. All Rights Reserved. Carbohydrate Digestion • Ultimate goal • Glucose for absorption and use • Hydrolysis via enzymes • Mouth • Amylase • Stomach • Stomach acid and protein-digesting enzymes • Role of fiber © 2016 Cengage Learning. All Rights Reserved. Intestinal Role in Digestion • Small intestine • Most carbohydrate digestion occurs here • Pancreatic amylase • Specific disaccharide enzymes • Maltase • Sucrase • Lactase • Large intestine • Fibers attract water © 2016 Cengage Learning. All Rights Reserved. Carbohydrate Digestion in the GI Tract © 2016 Cengage Learning. All Rights Reserved. Carbohydrate Absorption • Active transport • Glucose • Galactose • Facilitated diffusion • Fructose • Liver • Conversion of fructose and galactose © 2016 Cengage Learning. All Rights Reserved. Absorption of Monosaccharides © 2016 Cengage Learning. All Rights Reserved. Monosaccharides, the end products of carbohydrate digestion, enter the capillaries of the intestinal villi. Glucose is used by most cells in the body. In the liver, galactose and fructose share metabolic pathways with glucose. Small intestine Monosaccharides travel to the liver via the portal vein. Stepped Art Absorption of monosaccharides - Lactose Intolerance • Lactase activity • Highest immediately after birth • Declines with age • Symptoms of intolerance • Causes of intolerance beyond age • Prevalence • Trait has a genetic component © 2016 Cengage Learning. All Rights Reserved. Dietary Changes with Lactose Intolerance • Manage dairy consumption rather than restrict • GI bacteria • Fermented milk products • Individualized diets • Potential nutrient deficiencies • Riboflavin, vitamin D, and calcium © 2016 Cengage Learning. All Rights Reserved. Lactose in Selected Foods Foods Lactose (g) Whole-wheat bread, 1 slice 0.5 Dinner roll, 1 0.5 Cheese, 1 oz Cheddar or American 0.5 Parmesan or cream 0.8 Doughnut (cake type), 1 1.2 Chocolate candy, 1 oz 2.3 Sherbet, 1 c 4.0 Cottage cheese (low-fat), 1 c 7.5 Ice cream, 1 c 9.0 Milk, 1 c 12.0 Yogurt (low-fat), 1 c 15.0 NOTE: Yogurt is often enriched with nonfat milk solids, which increase its lactose content to a level higher than milk's. © 2016 Cengage Learning. All Rights Reserved. Carbohydrate Metabolism • Glucose is key player • Storing glucose as glycogen • Liver storage • Condensation into glycogen • Hydrolysis for release of glucose when needed • Muscle storage • Hoards glycogen for use during exercise © 2016 Cengage Learning. All Rights Reserved. Using Glucose for Energy • Fuels most of body’s cells • Preferred source for brain, nerve cells, and developing red blood cells • Cellular breakdown of glucose • Making glucose from protein • Amino acid conversion • Gluconeogenesis © 2016 Cengage Learning. All Rights Reserved. Ketone Bodies • Made from fat fragments • Inadequate supply of carbohydrates • Fat metabolism shifts • Ketone bodies alternative food source during starvation • Ketosis disturbs normal acid-base balance • Carbohydrate needs for protein sparing and prevention of ketosis • 50-100 grams/day • Using glucose to make fat © 2016 Cengage Learning. All Rights Reserved. The Constancy of Blood Glucose • Steady supply in blood stream • Intestines – food • Liver – glycogen • Blood glucose homeostasis • Insulin • Moves glucose from blood into cells • Glucagon and epinephrine • Brings glucose out from storage © 2016 Cengage Learning. All Rights Reserved. Maintaining Blood Glucose Homeostasis © 2016 Cengage Learning. All Rights Reserved. Balancing Within the Normal Range • Balanced meals at regular intervals • Diabetes • Insulin either inadequate or ineffective • Type 1 diabetes • Type 2 diabetes • Hypoglycemia • Prevalence © 2016 Cengage Learning. All Rights Reserved. Glycemic Response • Speed of glucose absorption, level of blood glucose, and return to normal glucose levels • Low glycemic response • Desired • High glycemic response • Fast absorption, surge in blood glucose, followed by a plunge below normal glucose levels • Glycemic index classifies foods • Limited utility © 2016 Cengage Learning. All Rights Reserved. Health Effects of Sugars • Pleasure in moderate amounts • Obesity and chronic disease • Nutrient deficiencies • Energy with few other nutrients • Discretionary kcalories • Honey • More energy per spoonful © 2016 Cengage Learning. All Rights Reserved. Dental Caries • Bacteria ferment sugars producing acid • Erodes tooth enamel • Food factors associated with tooth decay • Time of food in mouth • Sticky foods • Frequency of sugar consumption • Food choices • Factors associated with tooth decay © 2016 Cengage Learning. All Rights Reserved. Illustration of Dental Caries © 2016 Cengage Learning. All Rights Reserved. Enamel Caries Dentin Gum Crown Pulp (blood vessels, nerves) Bone Root canal Nerve Blood vessel Stepped Art Recommended Intakes of Sugars • Dietary Guidelines • Reduce the intake of kcalories from added sugars • DRI • Added sugars • No more than 25% of day’s total energy • Impact on other food groups • WHO and FAO recommendations • Restrict added sugar consumption to less than 10% of total energy © 2016 Cengage Learning. All Rights Reserved. Alternative Sweeteners • Artificial sweeteners • Non-nutritive sweeteners • Large doses and adverse effects • Stevia – herbal product • Generally recognized as safe (GRAS) • Sugar alcohols • Provide kcalories • Benefits and side effects © 2016 Cengage Learning. All Rights Reserved. Health Effects of Starch and Fibers • Heart disease • Whole grains • Sources • Soluble fibers • Sources • Improving heart disease risk factors • Diet composition for reducing heart disease risk © 2016 Cengage Learning. All Rights Reserved. Fibers and Other Health Issues • Diabetes • High-fiber foods • GI health • High-fiber foods • Ample fluids • Weight management • High-fiber foods and whole grains • Feeling of fullness © 2016 Cengage Learning. All Rights Reserved. Fiber and Cancer • High fiber diet protects against colon cancer • Fiber supplements • Food sources of dietary fiber • Phytochemicals • Preventing colon cancer • Diluting, binding, and removing • Bacterial fermentation © 2016 Cengage Learning. All Rights Reserved. Harmful Effects of Excessive Fiber Intake • • • • • Insufficient energy or nutrients Abdominal discomfort, gas, diarrhea GI obstruction Nutrient absorption Dietary goals • Balance, moderation, variety © 2016 Cengage Learning. All Rights Reserved. Characteristics, Sources, and Health Effects of Fibers Major Food Sources Types of Fibers Actions in the Body Probable Health Benefits Viscous, Soluble, More Fermentable • Barley, oats, oat bran, rye. fruits (apples, citrus), legumes (especially young green peas and black-eyed peas), seaweeds, seeds and husks, many vegetables, fibers used as food additives • Gums • Pectins • Psylliuma • Some hemicellulose • Lower blood cholesterol by binding bile • Slow glucose absorption • Slow transit of food through upper Gl tract • Hold moisture in stools, softening them • Yield small fat molecules after fermentation that the colon can use for energy • Increase satiety • Lower risk of heart disease • Lower risk of diabetes • Lower risk of colon and rectal cancer • Increased satiety, and may help with weight management Nonviscous, Insoluble, Less Fermentable • Brown rice, fruits, legumes, seeds, vegetables (cabbage, carrots, brussels sprouts), wheat bran, whole grains, extracted fibers used as food additives • • • • Cellulose • Lianins Resistant starch Hemicellulose • © 2016 Cengage Learning. All Rights Reserved. Increase fecal weight and speed fecal passage through colon Provide bulk and feelings of fullness • Alleviate constipation • Lower risk of diverticulosis, hemorrhoids, and appendicitis • Lower risk of colon and rectal cancer Recommended Intakes of Starch and Fibers • DRI for carbohydrates • 45 to 65 percent of energy requirement • RDA for carbohydrates • 130 grams per day • Fiber • DV: 11.5 grams per 1000 kcalories • DRI: 14 grams per 1000 kcalories • No UL © 2016 Cengage Learning. All Rights Reserved. Fiber in Selected Foods Grains Whole-grain products provide about 1 to 2 g (or more) of fiber per serving: • 1 slice of whole-wheat, pumpernickel, rye bread • 1 oz read-to-eat cereal (100% bran cereals contain 10 g or more) • ½ cooked barley, bulgur, grits, oatmeal Vegetables Most vegetables contain about 2 to 3 g of fiber per serving: • 1 c raw bean sprouts • ½ c cooked broccoli, brussels sprouts, cabbage, carrots, cauliflower, collards, corn, eggplant, green beans, green peas, kale, mushrooms, okra, parsnips, potatoes, pumpkin, spinach, sweet potatoes, swiss chard, winter squash • ½ c chopped raw carrots, peppers Fruits Fresh, frozen, and dried fruits have about 2 g of fiber per serving: • 1 medium apple, banana, kiwi, nectarine, orange, pear • ½ c applesauce, blackberries, blueberries, raspberries, strawberries • Fruit juices contain very little fiber Legumes Many legumes provide about 6 to 8 g of fiber per serving: • ½ c cooked baked beans, black beans, black-eyed peas, kidney beans, navy beans, pinto beans Some legumes provide about 5 g of fiber per serving: • ½ c cooked garbanzo beans, great northern beans, lentils, lima beans, split peas NOTE: Appendix H provides fiber grams for more than 2000 foods. © 2016 Cengage Learning. All Rights Reserved. Tips to Increase Fiber Intake Eat whole-grain breads that contain ≥3 g of fiber per serving. Eat whole-grain cereals that contain ≥5 g of fiber per serving. Tips to Increase Fiber Intake Eat raw vegetables. Eat vegetables (such as potatoes and zucchini) with their skins. Tips to Increase Fiber Intake Eat fresh and dried fruit for snacks. Eat fruits (such as apples and pears) with their skins. Tips to Increase Fiber Intake Add legumes to soups, salads, and casseroles. From Guidelines to Groceries • Grains • 1 ounce provides about 15g of carbohydrate • “Three are key” message • Vegetables • Corn, peas, and potatoes have higher starch content • Fruits • Milk and milk products • Protein foods © 2016 Cengage Learning. All Rights Reserved. Read Food Labels • Food labels list • Total carbohydrate • Starch, fibers, sugars • Sugars • Added and natural sugars © 2016 Cengage Learning. All Rights Reserved. Bread Labels Compared © 2016 Cengage Learning. All Rights Reserved. Carbs, kCalories, and Controversies Highlight 4 © 2016 Cengage Learning. All Rights Reserved. Carbohydrates’ kCalorie Contributions • Obesity and the link to carbohydrates • Total daily energy intakes have increased • Activity levels have declined • Increase in body weight • Epidemiological studies • Inverse relationship between carbohydrates and weight • Weight loss • kCalorie intake © 2016 Cengage Learning. All Rights Reserved. Energy Nutrients over Time © 2016 Cengage Learning. All Rights Reserved. Daily Energy Intake over Time © 2016 Cengage Learning. All Rights Reserved. Increases in Adult Body Weight over Time © 2016 Cengage Learning. All Rights Reserved. Sugars’ Share in the Problem • Increase in consumption of added sugars • High-fructose corn syrup • Body fat stores • Carbohydrate cravings • Self-imposed labeling of foods as good or bad • Carbohydrate “addiction” • Not physiological or pharmacological © 2016 Cengage Learning. All Rights Reserved. Appetite Control • Fructose and insulin • Flaws in plausibility • Food form – liquid or solid • Beverages can influence weight gains by providing energy but not satisfying hunger © 2016 Cengage Learning. All Rights Reserved. Insulin’s Response • Surge of insulin levels • How high the surge influences whether body stores or uses its glucose • Glycemic effect • Factors impacting glycemic effect • Glycemic index and body weight • Insulin resistance • Most often caused by being obese • Body’s insulin response © 2016 Cengage Learning. All Rights Reserved.
