Chapter 4 Carbohydrates: Sugar, Starch, Glycogen, and Fiber

1. Chapter 4 Carbohydrates: Sugar, Starch, Glycogen, and Fiber Nutrition: Concepts & Controversies, 12e Sizer/Whitney

2. Learning Objectives • Describe the major types of carbohydrates, and identify their food sources. • Describe the various roles of carbohydrates in the body, and explain why avoiding dietary carbohydrates may be ill-advised. • Summarize how fiber differs from other carbohydrates and how fiber may contribute to health.

3. Learning Objectives • Explain how complex carbohydrates are broken down in the digestive tract and absorbed into the body. • Describe how hormones control blood glucose concentrations during fasting and feasting. • Explain the term glycemic index and how it may relate to diet planning.

4. Learning Objectives • Describe the scope of the U.S. diabetes problem and educate someone about the long- and short-term effects of untreated diabetes and prediabetes. • Name components of a lifestyle plan to effectively control blood glucose and describe the characteristics of a diet that can assist in managing type 2 diabetes.

5. Learning Objectives • Compare the symptoms of postprandial hypoglycemia with those of fasting hypoglycemia, and name some diseases associated with the latter type. • Discuss current research regarding the relationships among dietary carbohydrates, obesity, diabetes, and other ills.

6. Carbohydrates • Ideal nutrients • Energy needs • Feed brain and nervous system • Keep digestive system fit • Keep your body lean • Digestible and indigestible carbohydrates • Complex vs. simple carbohydrates

7. A Close Look at Carbohydrates • Contain the sun’s radiant energy • Green plants • Photosynthesis • Glucose • Plants do not use all of the energy stored in their sugars • Carbohydrate-rich foods • Plants • Milk

8. Carbohydrate – Mainly Glucose – Is Made by Photosynthesis

9. Carbon dioxide Sun Energy Energy Oxygen Chlorophyll Glucose Water Fig. 4.1, p. 108

10. A Close Look at Carbohydrates - Sugars • Six sugar molecules • Monosaccharides • Glucose, fructose, galactose • Disaccharides • Lactose, maltose, and sucrose • Digestion of mono- and disaccharides • Chemical names end in -ose

11. How Monosaccharides Join to Form Disaccharides

12. Fructose Glucose Galactosea Three types of monosaccharides… …join together to make three types of disaccharides. Sucrose Maltose Lactoseb (fructose-glucose) (glucose-glucose) (glucose-galactose) aGalactose does not occur in foods singly but only as part of lactose. bThe chemical bond that joins the monosaccharides of lactose differs from those of other sugars and makes lactose hard for some people to digest—lactose intolerance (see later section). Fig. 4.2, p. 109

13. A note on the glucose symbol: The glucose molecule is really a ring of 5 Carbons and 1 oxygen plus a carbon “flag.” Carbons Oxygen For convenience, glucose is symbolized as or Fig. 4.2, p. 109

14. A Close Look at Carbohydrates – Starch • Polysaccharides • Starch • Plant’s storage form of glucose • Glycogen • Fiber • Nutrition • For a plant • For a human

15. How Glucose Molecules Join to Form Polysaccharides

16. Glucose Starch (unbranched) Starch (branched) Glycogen Cellulose Starch Glucose units are linked in long, occasionally branched chains to make starch. Human digestive enzymes can digest these bonds, retrieving glucose. Real glucose units are so tiny that you can’t see them, even with the highest-power light microscope. Glycogen Glycogen resembles starch in that the bonds between its glucose units can be broken by human enzymes, but the chains of glycogen are more highly branched. Cellulose (fiber) The bonds that link glucose units together in cellulose are different from the bonds in starch or glycogen. Human enzymes cannot digest them. Fig. 4.3, p. 110

17. A Close Look at Carbohydrates – Glycogen • Storage form of glucose • Animal bodies • Chains are longer than starch • More highly branched • Undetectable in meats

18. A Close Look at Carbohydrates - Fibers • Human digestive enzymes cannot break bonds • Bacteria in large intestine • Fermentation • Soluble vs. insoluble fibers

19. The Need for Carbohydrates • Critical energy source • Nerve cells and brain • Preferred dietary sources • Starchy whole foods • Complex carbohydrates • Vital roles in the functioning body

20. The Need for Carbohydrates • Weight loss • Caloric contribution • Conversion into fat storage • Refined sugars • Increase fiber-rich whole foods • Reduce refined white flour and added sugars

21. Why Do Nutrition Experts Recommend Fiber-Rich Foods? • Health benefits • Reduced risk of heart disease • Reduced risk of hypertension • Reduced risk of diabetes • Reduced risk of bowel disease • Promotion of healthy body weight • Sources of fiber

22. Characteristics, Sources, and Health Effects of Fibers

23. Fiber Composition of Common Foods

24. Why Do Nutrition Experts Recommend Fiber-Rich Foods? • Lower cholesterol and heart disease risk • Complex carbohydrates • More than just fiber • Viscous fiber • Cholesterol synthesis • Blood glucose control • Whole grains • Soluble fibers

25. One Way Fiber in Food May Lower Cholesterol in the Blood

26. Gallbladder stores bile 2. 1. Liver uses blood cholesterol to make bile 3. Intestine: bile aids digestion; binds to fiber 5. A little cholesterol in bile reabsorbed into the blood 4. Fiber and bile excreted in feces A. High-fiber diet Fig. 4.6a, p. 116

27. Gallbladder stores bile 2. 1. Liver uses blood cholesterol to make bile 3. Intestine: bile aids digestion 5. Much of the cholesterol in bile absorbed into the blood 4. Little bile excreted B. Low-fiber diet Fig. 4.6b, p. 116

28. Why Do Nutrition Experts Recommend Fiber-Rich Foods? • Maintenance of digestive tract health • All kinds of fiber • Ample fluid intake • Benefits of fiber • Constipation, hemorrhoids, appendicitis, diverticulosis

29. Diverticula

30. Diverticula Colon Fig. 4.7, p. 117

31. Diverticulum Fig. 4.7, p. 117

32. Why Do Nutrition Experts Recommend Fiber-Rich Foods? • Digestive tract cancer and inflammation • Ways fiber works against cancer • Dilution • Folate • Resident bacteria • Butyrate • Recommended dietary sources • Healthy weight management • Appetite control

33. Fiber Recommendations and Intakes • Few people in U.S. meet recommendations • 20-35 grams of fiber daily • Based on energy needs, age, and gender • Adding fiber to diet • Too much fiber? • Dangers of excess • Binders in fiber • Chelating agents • Cause of deficiencies

34. Usefulness of Carbohydrates

35. Refined, Enriched, and Whole-Grain Foods • Bread supplies much carbohydrate for many people • Kernel (whole grain) has four main parts • Germ • Endosperm • Bran • Husk

36. A Wheat Plant and a Single Kernel of Wheat

37. husk (chaff) beard Head kernels bran (14%) endosperm (83%) germ (2.5%) Stem A kernel of wheat A wheat plant Root Fig. 4.8, p. 120

38. Refined, Enriched, and Whole-Grain Foods • U.S. Enrichment Act of 1942 • Required additives • Addition in 1996 • Advantages of whole grains vs. enriched grains • Finding the whole grains in foods

39. Nutrients in Whole-Grain, Enriched White, and Unenriched White Breads

40. Bread Labels Compared

41. From Carbohydrates to Glucose – Digestion & Absorption • Starch and disaccharides are broken down • Monosaccharides for absorption • Starch • Begins in the mouth • Splits starch into maltose • Digestion ceases in the stomach • Digestion resumes in small intestine • Pancreas • Resistant starch

42. From Carbohydrates to Glucose – Digestion & Absorption • Sugars • Split to yield free monosaccharides • Enzymes on small intestine lining • Travel to the liver • Fiber • Fermented by bacteria in the colon • Odorous gas • Gradually increase fiber intakes

43. How Carbohydrate in Food Becomes Glucose in the Body

44. Esophagus Pancreas Liver Stomach Small intestine Large intestine (colon) Intestinal wall cells Capillary 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. An enzyme from the pancreas digests most of the starch to disaccharides. 2 1 1 3 Enzymes on the surface of cells that line the intestine split disaccharides to monosaccharides. 3 2 4 Monosaccharides enter capillaries, and are then delivered to the liver via the portal vein. 4 Fiber and resistant starch travel unchanged to the colon. The liver can convert galactose and fructose to glucose. 6 5 6 5 Key: galactose lactose sucrose maltose fiber Fig. 4.11, p. 124 starch

45. Why Do Some People Have Trouble Digesting Milk? • Ability to digest milk carbohydrates varies • Lactase • Made by small intestine • Symptoms of intolerance • Nausea, pain, diarrhea, and gas • Milk allergy • Nutritional consequences • Milk tolerance and strategies

46. The Body’s Use of Glucose • Basic carbohydrate unit used for energy • Body handles glucose judiciously • Maintains an internal supply • Tightly controlling blood glucose concentrations • Brain, nervous system, red blood cells

47. Splitting Glucose for Energy • Glucose is broken in half • Can reassemble • Broken into smaller molecules • Irreversible • Two pathways

48. Carbon atoms Bonds Glucose (6-carbon compound) 3-carbon compound Carbon dioxide 2-carbon compound 2 molecules of carbon dioxide Fig. 4.12, p. 126

49. Splitting Glucose for Energy • Glucose can be converted to fat • Fat cannot be converted to glucose • Dependence on protein when insufficient carbohydrate • Protein-sparing action • Ketosis • Shift in body’s metabolism • Disruption of acid-base balance • DRI minimum of digestible carbohydrate

50. How Is Glucose Regulated in the Body? • Two safeguard activities • Siphoning off excess blood glucose • Replenishing diminished glucose • Two hormones • Insulin • Signals body tissues to take up glucose • Glucagon • Triggers breakdown of glycogen • Epinephrine