Chapter 4: Carbohydrates, Sugars, Starches and Fiber

1. Chapter 4: Carbohydrates, Sugars, Starches and Fiber

2. What Are Carbohydrates? Produced by plants during photosynthesis After eating plant foods, humans convert the carbohydrates into glucose Glucose Most abundant carbohydrate Preferred source of energy for the blood, brain, and nervous system Carbohydrate-rich plant foods make up the foundation of diets all over the world

3. Classification of Carbohydrates Simple carbohydrates Monosaccharide Disaccharide Perceived as sweeter than complex carbohydrates Mixes with saliva and reacts with taste buds Oligosaccharides Complex carbohydrates Polysaccharides

4. Monosaccharides Three nutritionally important monosaccharides Glucose Fructose Galactose

5. Monosaccharides Glucose Blood glucose and blood sugar in the body Most abundant monosaccharide in the body Is the preferred and main source of energy for the brain and red blood cells Part of every disaccharide Only monosaccharide in starches

6. Monosaccharides Fructose Sweetest of natural sugars Found abundantly in fruits Part of high-fructose corn syrup Galactose Commonly occurs as part of dissaccharide lactose

7. The Structural Differences between Glucose, Galactose, and Fructose Figure 4.2

8. Disaccharides Three Disaccharides Sucrose Most common Lactose Maltose Least common Formed from digestion of starches

9. Monosaccharides Link to Form Disaccharides Figure 4.3

10. Polysaccharides Starch Plants store glucose in chains of starch Amylose Straight chain More resistant to digestion Resistant starch May improve health of digestive tract May improve glucose tolerance May stimulate growth of beneficial intestinal bacteria Amylopectin Branched chains Easier to digest

11. Polysaccharides Fiber Nondigestible polysaccharides Provides no energy Classification Soluble Pectins, beta-glucan, some gums, mucilage Easily fermented by intestinal bacteria Carbon dioxide, methane, some fatty acids Insoluble Cellulose, lignin, some hemicelluloses Not easily fermented

12. Fiber Health Benefits Soluble fibers Slow gastric emptying and may delay absorption of some nutrients Helps reduce serum cholesterol Improve appetite control Normalize blood glucose levels May help protect against colon cancer Insoluble fibers Relieves constipation Most plant foods contain both soluble and insoluble fibers

13. Polysaccharides Glycogen Storage form of glucose in animals Long, branched chains of glucose Stored in liver and muscle Liver glycogen response to blood glucose (BG) levels  BG  glycogen breakdown   BG Muscle glycogen can be broken down for energy for the muscle

14. The Comparison of Starch and Glycogen Molecules Figure 4.4

15. Oligosaccharides Similar in length to simple carbohydrates Similar in makeup to polysaccharides Humans lack the enzymes necessary to digest them Intestinal microflora digest and ferment them Cause bloating, discomfort, and flatulence Food sources Legumes, beans, cabbage, brussels sprouts, broccoli

16. The Structure of an Oligosaccharide Figure 4.7

17. Quick Review Complex carbohydrates Polysaccharides: starch, fiber, glycogen Fiber Soluble – fermented by intestinal bacteria; moves slowly Insoluble – moves quickly through and reduces constipation Functional – added to foods Oligosaccharides Contain three to ten units Part of cellulose in cell walls

18. Carbohydrate Digestion and Absorption Disaccharides and starches are digested to monosaccharides Monosaccharides are easily absorbed Fiber passes through the GI tract undigested

19. Figure 4.8a

20. Figure 4.8b

21. Figure 4.8c

22. Figure 4.8d

23. Absorption of Carbohydrates Once digested to monosaccharides Absorbed through the intestinal cell mucosa Transported to the liver via the portal vein Metabolic needs direct fate of the monosaccharides Galactose and fructose Used by the liver for energy Converted to glucose Glucose Used for energy Converted to glycogen through glycogenesis Converted to glycerol and fatty acids for storage in addipocytes

24. Glucose Is Stored in the Liver and Muscle Cells as Glycogen Figure 4.9

25. Quick Review Digestion of carbohydrates begins in the mouth Most carbohydrate digestion takes place in the small intestine Carbohydrates are broken down to monosaccharides for absorption Monosaccharides are converted to glucose in the liver and Used as energy Stored as glycogen in the liver and muscle cells Stored as glycerol and fatty acids in the adipocytes Fiber travels to the colon undigested and most is eliminated from the body

26. Lactose Intolerance Deficiency of lactase, the enzyme that digest lactose Maldigestion – inability to digest lactose due to low levels of the enzyme Intolerance Maldigestion resulting in nausea, cramps, bloating, flatulence, and diarrhea

27. Functions of Carbohydrate Provide energy 4 kilocalories per gram Maintain blood glucose Carbohydrate intake Glycogenolysis > 4 hours after a meal Spare protein Prevents the need for glyconogenesis Prevents ketosis

28. How to Maintain Blood Glucose Levels Goal for blood glucose is 70–100 mg/dl Insulin – lowers blood glucose levels Needed for glucose to enter the cell from the blood stream Exception: liver, kidney, and brain cells Helps convert glucose to glycogen through glycogenesis Helps convert glucose to fatty acids through lipogenesis Inhibits lipolysis Glucagon – increases blood glucose levels Stimulates the release of glucose into the blood Stimulates glycogenolysis Stimulates gluconeogensis

29. Insulin and Glucagon Regulate Glucose Metabolism Figure 4.10

30. How to Maintain Blood Glucose Levels Epinephrine and norepinephrine – increases blood glucose Stimulate glycogenolysis and gluconeogenesis Cortisol – increases blood glucose Stimulates gluconeogensis Reduces uptake of glucose by the muscle cells Growth hormone – increases blood glucose Stimulates fat breakdown for energy Reduces uptake of glucose by the muscles Increase glucose production in the liver

31. Quick Review Glucose is the body’s preferred source of energy Especially the brain and red blood cells Adequate carbohydrate intake Maintains blood glucose levels Spares protein Prevents ketosis Blood glucose levels are maintained by two hormones Insulin which lowers blood glucose levels Glucagon which raises blood glucose levels Epinephrine, norepinephrine, corisol, and growth hormone raise blood glucose levels.

32. Glycemic Index Classifies the effects of carbohydrate-containing foods on blood glucose May be helpful for diabetics Glycemic index (GI) refers to the measured upward rise, peaks, and falls of blood glucose following consumption of high-carbohydrate food Ranks foods according blood glucose

33. Glycemic Load Glycemic load (GL) – adjust GI by taking into account the amount of carbohydrate consumed in a typical serving of food Factors affecting GI Ripeness of fruit Cooking Processing Size of food pieces Amount of fiber Combinations of food eaten

34. Glycemic Index and Glycemic Load Usefulness of GI and GL for disease prevention and weight management is controversial Is helpful in educating people about Carbohydrate content of foods Portion sizes Serving numbers

35. Dietary Fiber Benefits Helps lower risk of Bowel irregularity Obesity Heart disease Cancer Diabetes mellitus

36. Dietary Fiber Chronic constipation can lead to diverticulosis and diverticulitis Prevention of constipation and diverticulosis Insoluble fiber helps reduce transit time of foods in the colon Soluble fiber helps make stool easier to pass by increasing bulk and softening texture Figure 4.12

37. Dietary Fiber Prevention of heart disease and diabetes Viscous, soluble fiber helps lower elevated blood cholesterol levels Interferes with reabsorbtion of bile acid Figure 4.13

38. Dietary Fiber Slow moving, viscous, soluble fiber may reduce the rate which fat and carbohydrate are absorbed Decreasing level of fat in blood and improving insulin sensitivity, decrease risk of heart disease Insoluble fiber has been shown to promote heart health Viscous soluble fiber helps slow digestion and absorption helping control blood glucose levels

39. Dietary Fiber Fiber helps reduce the incidence of several cancers Decreases the amount of time cancer-promoting substances spend in contact with the intestinal lining Encourages the growth of colon-friendly bacteria Reduces acid in the colon Helps prevent obesity Increase satiety Reduce food intake Caution: Increase dietary fiber and fluid intake gradually

40. Quick Review Glycemic index (GI) ranks foods according to effects on glucose levels compared to white bread or pure glucose Glycemic load adjust for serving size Foods that contain high fiber or are eaten with protein and fat generally have a lower GI. High-fiber diet health benefits include reduced risk of Constipation Diverticulosis Heart disease Obesity Diabetes Mellitus Cancer

42. Importance of Whole Grains

43. Carbohydrate Sources Best choices should include nutrient-dense, low-saturated fat foods, simple carbohydrates, fiber, complex carbohydrates

44. Food Sources of Carbohydrates Figure 4.14

45. Food Sources of Fiber Figure 4.15

46. Quick Review Best sources of carbohydrates are Fresh fruits and vegetables Whole grains Excellent sources of fiber are Whole grains Fruits Vegetables Packaged foods can be good sources of starch and fiber Read label carefully Avoid too much sugar, fat, and kilocalories • Legumes • Low-fat dairy products • Legumes • Nuts • Seeds

47. Diabetes Mellitus Occurs when an individual either doesn’t make enough, or is unable to utilize, the hormone insulin to regulate blood glucose levels Epidemic Sixth leading cause of death in the United States Costs the U.S. almost $100 billion annually Number of people with diabetes is rising annually

48. Diabetes Mellitus No Insulin Available or Cells Resistant Consume Carbohydrates Blood Glucose Rises Liver Breaks Down Glycogen and Produces Glucose from Non-Carbohydrate Sources Cell Starves Blood Glucose Rises Body Uses Fat for Fuel Ketoadicosis

49. Forms of Diabetes Type 1 Usually begins in childhood or early adulthood 5–10% of diabetics Immune system destroys beta cells of the pancreas No insulin produced Common symptoms of elevated blood sugar Polydipsia Polyuria Polyphagia Require insulin and frequent blood glucose monitoring

50. Forms of Diabetes Type 2 Overweight individuals develop this form frequently 90–95% of diabetics Can go undiagnosed Damages vital organs without individual being aware of it Polycystic ovary syndrome Hormonal imbalance in women Have higher incidence of insulin resistance and hyperinsulinemia Increased risk of developing type 2 diabetes