The Carbohydrates: Sugars, Starches, and Fibers

1. The Carbohydrates: Sugars, Starches, and Fibers Chapter 4

2. Chapter 4 Objectives • Identify the monosaccharides, disaccharides, and polysaccharides common in nutrition by their chemical structures and major food sources. • Classify carbohydrates as mono-, di-, or polysaccharides. • Explain the two major types of dietary fibers and their uses in the body. • Summarize carbohydrate digestion and absorption. • Trace the digestion and absorption of carbohydrates. • List the enzymes used in the digestion of carbohydrates. • Describe lactose intolerance symptoms, prevalence, and treatment. • Explain how the body maintains its blood glucose concentration and what happens when blood glucose rises too high or falls too low. • List the major uses of glucose in the body. • Discuss the hormones used by the body to maintain normal blood glucose concentration. • List the major types of diabetes. • Explain glycemic load and the pros and cons of its use in meal planning. • Describe how added sugars can contribute to health problems. • Identify the major sources of added sugars in the diet. • Describe the effect of added sugars on dental health. • List the common alternatives to sugar in the diet. • Identify the health benefits of, and recommendations for, starches and fibers. • Identify the health benefits of a diet rich in starch and fiber. • Identify the Daily Value and DRI for fiber and methods to increase fiber in the diet.

3. Introduction • Brain • Glucose – RDA 130g/day • Muscles • Glucose • Glycogen • Fat • Sources of carbohydrates (SMURF) • “Fattening” – mistaken thinking

4. Chemist’s View of Carbohydrates • Carbohydrate family • Atoms and chemical bonds • Monosaccharides • Chemical shorthand • Glucose, fructose, galactose • Disaccharides • Maltose, sucrose, lactose • Polysaccharides

5. Atoms and Their Bonds

6. Chemist’s View of Carbohydrates • Monosaccharides • Chemical formula: C6H12O6 • Differing sweetness • Fructose • Sweetest of the sugars • Glucose – blood sugar • Part of every disaccharide • Galactose • Only in a few foods

7. Chemical Structure of Glucose

8. The Monosaccharides Descending order of sweetness

9. Chemist’s View of Carbohydrates • Disaccharides • Pairs of three monosaccharides • Sucrose – glucose and fructose • Maltose – two glucose units • Lactose – galactose and glucose • Condensation • Links two monosaccharides together • Hydrolysis • Breaks a disaccharide in two

10. Condensation and Hydrolysis of a Disaccharide

11. Chemist’s View of Carbohydrates • Polysaccharides • Glycogen • Storage form of energy in the body • Glucose units • Starch • Storage form of energy in plants • Glucose units

12. Glycogen Starch (amylopectin) Starch (amylose) 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. A starch molecule contains hundreds of glucose molecules in either occasionally branched chains (amylopectin) or unbranched chains (amylose). Stepped Art Figure 4-6 p99

13. Chemist’s View of Carbohydrates • Polysaccharides • Fibers • Differ from starches: bonds cannot be broken down by human digestive system • Soluble fibers – oats, barley, legumes, citrus • Lower cholesterol and blood sugar • Insoluble fibers – bran, vegetables • Promote bowel health and movement

14. Chemist’s View of Carbohydrates • Polysaccharides • Fibers • Functional fibers • Naturally occurring, repurposed • Ex: Fiber One bars • Resistant starches • Not digested or absorbed at all • Ex: just-ripe bananas, cooked potatoes, rice, pasta • (Phytic acid) • (not a fiber, but found in fiber-rich foods, often) • (binds with minerals, blocks some absorption)

15. Chemist’s View of Carbohydrates • Polysaccharides • Fibers • (Phytic acid) • (not a fiber, but often found in fiber-rich foods) • (binds with minerals, blocks some absorption)

16. The Bonds of Starch and Cellulose Compared

18. Carbohydrate Digestion • Goal of digestion: glucose for body to use • Breakdown, absorb (monosaccharides) • Hydrolysis via enzymes • Mouth: short timespan • Amylase (starch, maltose) • Stomach: ceases • Stomach acid & protein-digesting enzymes • Fibers linger, delay gastric emptying

19. Carbohydrate Digestion • Small intestine: most of the work • Pancreatic amylase: polysaccharides • Specific disaccharide enzymes work • Maltase • Sucrase • Lactase • Large intestine: fibers remain • Attract water • GI bacteria ferment  water, gas, short-chain fatty acids (i.e. some energy)

21. Carbohydrate Absorption • Remember: the goal is glucose! • Small % glucose absorbed through mouth • Active transport • Glucose • Galactose • Facilitated diffusion • Fructose • Liver • Conversion of fructose and galactose

22. Small intestine Monosaccharides, the end products of carbohydrate digestion, enter the capillaries of the intestinal villi. Glucose is used by most cell sin the body. In the liver, galactose and fructose share metabolic pathways with glucose. Monosaccharides travel to the liver via the portal vein. Stepped Art Figure 4-9 p103

23. Lactose Intolerance • Lactase activity • Highest immediately after birth • Declines with age • Symptoms of intolerance • Bloating, discomfort, diarrhea, gas • Secondary intolerance: damaged intestinal villi (disease, meds, malnutrition) • Prevalence • Genetically determined

24. Lactose Intolerance • Dietary changes • Manage, not eliminate • <6g lactose (1/2 cup milk): asymptomatic • Fermented milk products • GI bacteria • Individualized diets • Potential nutrient deficiencies: • Riboflavin, vitamin D, and calcium

25. Lactose in Selected Foods

27. Carbohydrate Metabolism • Glucose is key player • Storing glucose as glycogen • Liver storage • Condensation into glycogen • Hydrolysis for release of glucose when needed • Muscle storage • Selfishly hoards glycogen

28. Carbohydrate Metabolism • Glucose for energy • Fuels most of body’s cells • Preferred source for brain, nerve cells, and developing red blood cells • Cellular breakdown of glucose  CO2 + H2O • Making glucose from protein • Amino acid conversion • Gluconeogenesis

29. Carbohydrate Metabolism • Ketone bodies from fat fragments • Inadequate supply of carbohydrates • Fat metabolism shifts • Ketone body formation – starvation • Ketosis – acid-base balance • Carbohydrate needs for protein sparing and prevention of ketosis • Using glucose to make fat

31. The Constancy of Blood Glucose • Steady supply in blood stream • Intestines – food • Liver – glycogen • Blood glucose homeostasis • Insulin • Glucose from blood into cells • Glucagon & epinephrine • Brings glucose out from storage

32. Maintaining Blood Glucose Homeostasis

33. The Constancy of Blood Glucose • Balancing within the normal range • Balanced meals at regular intervals • Diabetes • Insulin is either inadequate or ineffective • Type 1 diabetes • Type 2 diabetes • Hypoglycemia • Prevalence

34. The Constancy of Blood Glucose • Glycemic response • Speed of glucose absorption, level of blood glucose, and return to normal glucose levels • Low glycemic response • Desired • High glycemic response • Glycemic index • Benefits • Utility

36. Health Effects of Sugars • Pleasure in moderate amounts • Obesity and chronic disease • HFCS: glucose and fructose • Normally about 50/50 (like sucrose) • Association between overweight and sweet desserts and soft drinks • Added sugars (fructose, esp) favor fat-making pathways, impair fat-clearing pathways  poor lipid panel

37. Health Effects of Sugars • Nutrient deficiencies • Energy with few other nutrients • Discretionary kcalories • Honey = Agave = Maple Syrup = Sugar • Any health benefits are minor • Choose nutrient dense first

38. Health Effects of Sugars • Dental caries • Bacteria ferment sugars producing acid • Food factors associated with tooth decay • Time of food in mouth • Sticky foods • Frequency of sugar consumption • Food choices • Factors associated with tooth decay

39. Enamel Caries Crown Dentin Gum Pulp (blood vessels, nerves) Bone Root canal Nerve Blood vessel Stepped Art Figure 4-11 p111

40. Recommended Intakes of Sugars • Dietary Guidelines • Reduce the intake of kcalories from added sugars • DRI • Added sugars: <25% of kcal • Impact on other food groups • WHO and FAO recommendations • <10% of kcal

41. Alternative Sweeteners • Artificial sweeteners • Non-nutritive sweeteners • Large doses and adverse effects • Stevia – an herbal product • Generally recognized as safe (GRAS) • Sugar alcohols • Provide kcalories • Benefits and side effects

43. Health Effects of Starch and Fibers • Heart disease • Soluble fibers: oat bran, barley, legumes • How? • Soluble fiber binds with bile acids  excretion  liver must use own cholesterol • Fiber fermentation in colon  liver stops making cholesterol • Improving heart disease risk factors

44. Health Effects of Starch and Fibers • Diabetes • Increase transit time, slows glucose absorption, more stable blood sugars • GI health • Incr stool weight, ease passage, reduce transit time • Ample fluids • Stimulates muscles – retain strength

45. Health Effects of Starch and Fibers • Cancer • Dietary fiber and colon cancer • Food, not supplements • Sources of dietary fiber • Phytochemicals • Preventing colon cancer • Diluting, binding, and removing • Bacterial fermentation

46. Health Effects of Starch and Fibers • Weight management • High-fiber foods and whole grains • Feeling of fullness • Bulk to diet, nutritious, economical

47. Health Effects of Starch and Fibers • Excessive fiber • Insufficient energy or nutrient needs • Abdominal discomfort, gas, diarrhea • GI obstruction (too much, too soon) • Nutrient absorption • Dietary goals • Balance, moderation, variety

48. Characteristics, Sources, & Health Effects of Fibers

49. Recommended Intakes of Starch & Fibers • DRI for carbohydrates • 45 to 65% of energy requirement • RDA for carbohydrates • 130 grams per day • Fiber • DRI: 14 grams per 1000-kcalories (no UL)

50. Fiber in Selected Foods