Carbohydrates: Plant-Derived Energy Nutrients

1. 4 Carbohydrates: Plant-Derived Energy Nutrients

2. What Are Carbohydrates? • One of the three macronutrients • Important source of energy for all cells • Preferred energy source for nerve cells • Composed of carbon, hydrogen, oxygen • Good sources: fruits, vegetables, grains

3. What Are Carbohydrates? • Glucose • The most abundant carbohydrate • Produced by plants through photosynthesis

5. What Are Carbohydrates? • Simple carbohydrates • Contain one or two molecules • Commonly referred to as sugars • Monosaccharides contain one molecule • Glucose, fructose, and galactose • Disaccharides contain two molecules • Lactose, maltose, and sucrose

8. What Are Carbohydrates? • Complex carbohydrates • Oligosaccharides contain 3 to 10 monosaccharides • Most polysaccharides consist of hundreds to thousands of glucose molecules • Starch, glycogen, most fibers

10. Complex Carbohydrates • Starch • Plants store carbohydrates as starch • Amylose—straight chain of glucose • Amylopectin—branched chain of glucose • Resistant starch (fiber)—glucose molecules linked by beta bonds are largely indigestible • Sources: grains, legumes, fruits, vegetables

11. Complex Carbohydrates • Glycogen • Storage form of glucose for animals (humans) • Not found in food and therefore not a source of dietary carbohydrate • Stored in the liver and muscles

12. Complex Carbohydrates • Fiber • Composed of long polysaccharide chains • Dietary fibers are non-digestible parts of plants • Functional fibers are non-digestible forms of carbohydrates extracted from plants or manufactured in a laboratory and have known health benefits • Total fiber = Dietary fiber + Functional fiber

13. Complex Carbohydrates • Soluble fibers • Dissolve in water; viscous and gel-forming • Fermentable, digested by intestinal bacteria • Associated with risk reduction of cardiovascular disease and type 2 diabetes • Examples: pectin, gum, mucilage • Found in citrus fruits, berries, oats, beans

14. Complex Carbohydrates • Insoluble fibers • Do not dissolve in water, nonviscous • Cannot be fermented by bacteria in the colon • Promote regular bowel movements, alleviate constipation, and reduce diverticulosis • Examples: lignins, cellulose, hemicelluloses • Good sources: whole grains, seeds, legumes, fruits, and vegetables ABC Video Whole Grains

15. Carbohydrate Digestion Carbohydrate Digestion • Salivary amylase • Enzyme that begins carbohydrate digestion in the mouth • Breaks carbohydrates down to maltose • Carbohydrate digestion does not occur in the stomach • Stomach acids inactivate salivary amylase

16. Carbohydrate Digestion • Most chemical digestion of carbohydrates occurs in the small intestine • Pancreatic amylase • Enzyme produced in the pancreas and secreted into the small intestine • Digests carbohydrates to maltose

17. Carbohydrate Digestion • Additional enzymes in the microvilli digest disaccharides to monosaccharides • Maltase • Sucrase • Lactase • Monosaccharides are absorbed into the cells lining the small intestine and then enter the bloodstream

19. Carbohydrate Digestion • All monosaccharides are converted to glucose by the liver • Glucose circulating in the blood is our primary energy source • Excess glucose is stored as glycogen in the liver and muscles

21. Carbohydrate Digestion • We do not have the enzymes necessary to digest fiber • Bacteria in the large intestine can break down some fiber • Most fiber remains undigested and is excreted in the feces Carbohydrate Absorption

22. Blood Glucose Regulation • Blood glucose must be closely regulated • Hormones control blood glucose levels: • Insulin • Glucagon • Epinephrine • Norepinephrine • Cortisol • Growth hormone Hormonal Control of Blood Glucose

23. Blood Glucose Regulation: Insulin • Secreted by beta cells of the pancreas • Stimulates glucose transporters (carrier proteins) to help take glucose from the blood across the cell membrane • Stimulates the liver to take up glucose and convert it to glycogen

25. Blood Glucose Regulation: Glucagon • Secreted by alpha cells of the pancreas • Stimulates the liver to convert glycogen to glucose • Stimulates gluconeogenesis, the production of glucose from amino acids

27. Blood Glucose Regulation: Epinephrine and Norepinephrine • Secreted by the adrenal glands and nerve endings when blood glucose is low • Increase glycogen breakdown in the liver, releasing glucose into the blood • Responsible for our “fight-or-flight” reactions to danger

28. Blood Glucose Regulation: Cortisol and Growth Hormone • Secreted by the adrenal glands to act on the liver, muscle, and adipose tissue • Cortisol increases gluconeogenesis and decreases muscle glucose use • Growth hormone decreases muscle glucose uptake, increases fatty acid mobilization and use, and increases liver glucose output

29. Blood Glucose Regulation: Glycemic Index • A food’s potential to raise blood glucose • Foods with a high glycemic index cause a sudden surge in blood glucose, triggering a large increase in insulin, which may be followed by a dramatic fall in blood glucose • Foods with a low glycemic index cause low to moderate fluctuations in blood glucose

30. Blood Glucose Regulation: Glycemic Index • Not always easy to predict • Food’s absorption rate varies with type of carbohydrate, preparation methods, and its fat and fiber content • Most foods are eaten in combination in a meal

31. Blood Glucose Regulation: Glycemic Load • Used to determine the effect of a food on a person’s glucose response • Grams of carbohydrates in a food are multiplied by the glycemic index • Glycemic index and glycemic load remain controversial • Evidence of health benefits is weak

32. Blood Glucose Regulation: Value of Lower Glycemic Index • Less fluctuations in blood glucose • Risk reduction for heart disease and colon cancer • High fiber intake helps to improve fat levels in the blood (higher HDL and lower LDL) • Foods with lower glycemic index: • Beans, fresh vegetables, whole wheat

34. The Role of Carbohydrates • Energy • Each gram of carbohydrate: 4 kcal • Red blood cells use only glucose for energy • Both carbohydrates and fats supply energy for daily activities • Glucose is especially important for energy during exercise

36. The Role of Carbohydrates • Ketosis • Fat breakdown during fasting forms ketones • Excess ketones increase blood acidity and cause ketoacidosis • Sufficient energy from carbohydrates prevents ketone production as alternate energy source Fad Diets

37. Carbohydrates Spare Protein • Gluconeogenesisoccurs when a diet is deficient in carbohydrate • The body will make its own glucose from protein • Amino acids from these proteins cannot be used to make new cells, repair tissue damage, support the immune system, or perform any of their other functions

38. Complex Carbohydrates Have Health Benefits • Fiber • May reduce the risk of colon cancer • Helps prevent hemorrhoids, constipation, and other intestinal problems • May reduce the risk of diverticulosis • May reduce the risk of heart disease • May enhance weight loss • May lower the risk of type 2 diabetes Diverticulosis and Fiber

41. How Much Carbohydrate? • Recommended Dietary Allowance (RDA) is 130 grams/day to supply adequate glucose to the brain • Acceptable Macronutrient Distribution Range (AMDR) is 45% to 65% of daily calories • Focus on fiber-rich carbohydrate foods

43. Simple Carbohydrates • Diets high in simple sugars: • Can cause tooth decay • May increase “bad cholesterol” • May decrease “good cholesterol” • May contribute to obesity ABC Video Sugar and Processed Food

45. Complex Carbohydrates • Most Americans eat too little complex carbohydrates • Enriched foods are foods in which nutrients that were lost during processing have been added back so the food meets a specified standard • Fortified foods have nutrients added that did not originally exist in the food (or existed in insignificant amounts)

47. Complex Carbohydrates • Adequate Intake (AI) for fiber • 25 g per day for women • 38 g per day for men, or • 14 g of fiber for every 1,000 kcal per day • It is best to get fiber from food (also a source of vitamins and minerals) • An adequate fluid intake (at least 8 oz/day) with high-fiber diets is recommended