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Chapter 4: Carbohydrates

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This chapter explores carbohydrates, the essential macronutrients synthesized by plants. It covers simple sugars, including monosaccharides like glucose, fructose, and galactose, and their roles in the body. We delve into disaccharides such as sucrose and lactose, explaining their sources and functions. Additionally, complex carbohydrates like starch and glycogen are examined, highlighting their significance for energy storage. The chapter emphasizes dietary fiber, its types, benefits, and the effects of excessive fiber intake. Lastly, it discusses carbohydrate digestion and considerations for lactose intolerance.

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Chapter 4: Carbohydrates

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  1. Chapter 4: Carbohydrates

  2. Plants Synthesize Glucose

  3. Simple Sugars • Monosaccharides • Single sugar molecules • Disaccharides • Pairs of monosaccharides

  4. Glucose Fructose Galactose Monosaccharides

  5. Glucose (Dextrose) • Not used as a sweetener • Source: breakdown of starch and other sugars

  6. Glucose in the Body • Form of sugar found in the blood • Only energy source for the brain • Quick energy for muscles

  7. Fructose (fruit sugar) • Sweetest monosaccharide • Metabolized to glucose in the liver • Found in fruit, honey, and high fructose corn syrup • Is in sucrose (table sugar)

  8. Galactose • Not used as sweetener • Usually bound with glucose (lactose or milk sugar) • Converted to glucose in the liver • Available fuel source

  9. Disaccharides: Pairs of Sugars • “Simple sugars” • Linked monosaccharides • Always contain glucose

  10. Sucrose • Glucose + Fructose • Table sugar • Soft drinks, candy, ice cream • Baked goods, jelly, cereal

  11. Lactose • Galactose + Glucose • Dairy products • Increases calcium absorption

  12. Maltose (malt sugar) • Glucose + Glucose • Sprouting seeds • Digestion of starch • Fermentation • Alcohol production

  13. Complex Carbohydrates Polysaccharides: Starch & Glycogen • Amylose: straight chain digestible starch • Amylopectin: branched chain digestible starch • Dietary fiber: non-digestible

  14. Oligosaccharides • 3-10 monosaccharides • Found in beans and legumes • Not digested • Metabolized by bacteria in the large intestine • Beano®

  15. Polysaccharides: Starch • 3,000 or more monosaccharides bound together • Plant storage of glucose • Two forms • Amylose--straight chain polymer • Amylopectin--highly branched polymer

  16. Polysacchai\rides

  17. Sources of Starch • Grain products: bread, cereal, pasta • Some “starchy” vegetables: corn, peas, carrots, potatoes

  18. Glycogen • Storage form of CHO for animals and human • Structure similar to amylopectin • More sites for enzyme action • Found in the liver and muscles

  19. Glycogen Sources • Dietary: insignificant • Made in the body • Stored in the liver and muscles

  20. Dietary Fiber • Plant cells • Cannot be digested by humans • Humans lack necessary enzymes to break the bonds

  21. Dietary Fiber Found only in plants • Whole grains • Fruits • Vegetables

  22. Types of Fiber Insoluble fiber • Cellulose, hemicellulose, lignin • Does not dissolve in water • Not fermented by bacteria in the colon • Tough, fibrous parts of vegetables • Cereal bran, whole grains, fruit

  23. Types of Fiber Soluble fiber • Gum, Pectin, Mucilage • Fermented in colon • Sources: Fruits, vegetables, oats, beans, rice bran, psyllium seed

  24. Soluble and Insoluble Fiber

  25. Health Benefits of Insoluble Fiber • Decreases intestinal transit time • Promotes regularity, softer stools • Reduces constipation • Reduces risk of hemorrhoids (varicose veins in the rectum) caused by constipation

  26. Health Benefits of Insoluble Fiber • Reduces risk of diverticulosis • Outpouching of intestinal wall • Diverticulitis: inflamed pouches • High fruit and vegetable intake seems to reduce risk of colon cancer, though fiber may not be the factor

  27. Diverticula

  28. Health Benefits of Soluble Fiber • Associated with reduced risk of cardiovascular disease • Slows absorption of glucose from the small intestine • Appears to reduce risk of diabetes • May help with blood glucose control (but requires very large amounts of fiber)

  29. Health Benefits of All Fiber Weight management • Bulky, high-fiber foods fill you up • Have low energy density • May reduce risk of obesity

  30. Negative Effect of Excessive Fiber • >60 g/day • Bind minerals (calcium, zinc, iron) • Satiety without adequate nutrients, especially in children • Diarrhea • Constipation: if inadequate water can result in bowel obstruction

  31. CHO in Food

  32. Carbohydrate Digestion

  33. Effects of Cooking • Softens fibrous tissues • Easier to chew and swallow

  34. Digestion of Carbohydrate in the Mouth • Saliva contains amylase • Starch is broken down to shorter saccharides • Taste the sweetness with prolong chewing • Proceeds down the esophagus

  35. Digestion of Carbohydrate in the Stomach • The acidic environment stops the action of salivary amylase • No further starch digestion occurs

  36. In the Small Intestine • Pancreatic amylase is released • Intestinal cells release enzymes Maltose + maltase glucose + glucose Sucrose + sucrase glucose + fructose Lactose + lactase glucose + galactose • Monosaccharides are absorbed

  37. Lactose Intolerance • Reduction in lactase • Lactose is undigested and not absorbed • Lactose is metabolized by large intestinal bacteria • causes gas, bloating, cramping, discomfort • Primary lactose intolerance disease • Secondary lactose intolerance disease

  38. What To Do If You Are Lactose Intolerant • Determine amount you can tolerate • Eat dairy with fat • Cheese & yogurt are usually tolerated well • Use of Lact-Aid

  39. CHO Digestion

  40. CHO Absorption Glucose and Galactose • Active absorption • Energy is expended • Going from low to high concentration gradient Fructose • Facilitated diffusion using a carrier • No energy expended

  41. Portal Vein • Transport absorbed monosaccarhides • Delivers them to the liver Liver can: • transform fructose/galactose into glucose • release them into the blood stream • store as gylcogen (or fat)

  42. Uses of Glucose Energy • Brain’s only source • Muscle – quick energy Glycogen • Muscle: used by individual muscle • Liver: maintain blood sugar Excess converted to fat • Stored in fat cells • Future energy use as fat

  43. Regulation of Blood Glucose • Hyperglycemia • Hormone regulates • Insulin • Hypoglycemia • Hormones regulate • Glucagon • Epinephrine

  44. Blood Glucose Control • Role of the liver • Regulates glucose that enters bloodstream • Role of the pancreas • Release of insulin • Release of glucagon

  45. Functions of Insulin • Promotes glycogen synthesis • Increases glucose uptake by the cells • Reduces gluconeogenesis • Net effect: lowers the blood glucose

  46. Functions of Glucagon • Breakdown of glycogen • Enhances gluconeogenesis • Net effect: raises blood glucose

  47. Epinephrine/ Norepinephrine • “fight or flight” response • breakdown glycogen • raises blood glucose

  48. Diabetes Mellitus-Type 1 • Genetic link • Immunological disorder • Associated with early introduction of cow’s milk • Absence of insulin • Insulin dependent • Hyperglycemia

  49. Treatment for Type 1 • CHO counting • Insulin therapy • Risk for heart disease, kidney damage, other complications

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