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Energy Metabolism

Energy Metabolism. Utilization of energy-yielding nutrients for fuel. Metabolism of Nutrients. Once absorbed, energy-yielding nutrients are transported to cells Further metabolism (processing) occurs

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Energy Metabolism

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  1. Energy Metabolism Utilization of energy-yielding nutrients for fuel

  2. Metabolism of Nutrients Once absorbed, energy-yielding nutrients are transported to cells Further metabolism (processing) occurs Metabolic pathways: series of reactions that transform nutrients into final product that can be used by the body Catabolic pathways release energy trapped in chemical bonds Energy converted into ATP ATP is the energy currency of the cell

  3. ATP: Adenosine triphosphate

  4. Elimination of Metabolic Wastes: Body Organ Systems

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

  6. Introduction • Carbohydrates=energy fuel • For the brain: glucose • For muscles: glucose, glycogen, fat • Sources of carbohydrates? • “Fattening” – overgeneralization

  7. Carbohydrate Family • Abbreviation: CHO • Sugars (simple CHO) • Monosaccharides • Chemical shorthand: C6H12O6 • Glucose, fructose, galactose • Disaccharides • Maltose, sucrose, lactose • Polysaccharides (complex CHO)

  8. Chemist’s View of Monosaccharides Fructose

  9. Monosaccharides • Same numbers and kinds of atoms • Differing structure and sweetness • Glucose – blood sugar • Part of every disaccharide • Fructose • Sweetest of the sugars • Galactose • Only in a few foods

  10. Disaccharides • Pairs of three monosaccharides • Maltose – two glucose units • Sucrose – glucose and fructose • Lactose – galactose and glucose • Condensation • Links two monosaccharides together • Hydrolysis • Breaks a disaccharide in two

  11. Polysaccharides • Glycogen • Storage form of energy in muscle and liver • Glucose units • Starch • Storage form of energy in plants • Glucose units • Fibers • Not digestible, but very beneficial

  12. Fibers • Differ from starches • Soluble fibers • Mix with water - form a gel • Slow transit time in colon • Insoluble fibers • Do not mix with water or form a gel • Speed transit time in colon • Both forms of fiber slow gastric emptying

  13. Whole Grains • Bran layers: good source of fiber and vitamins • Germ: good source of vegetable oils and vitamin E • Endosperm: contains starch and some protein

  14. Carbohydrates in whole foods, such as fresh fruit, dairy or whole grains, are in their natural state • Refining CHO separates the CHO from vitamins, minerals, fiber, and phytochemicals • Whole: all edible parts present • Refined: some edible parts removed Whole vs. Refined Foods

  15. Digestion and Absorption of CHO

  16. Small intestine Absorption of CHO Monosaccharides, the end products of carbohydrate digestion, enter the capillaries of the intestinal villi. In the liver, galactose and fructose are converted to glucose. Monosaccharides travel to the liver via the portal vein.

  17. Fiber slows nutrient absorption

  18. More Health Benefits of Fiber • Diets high in fiber, or indigestible carbohydrates, can relieve or prevent certain bowel disorders: • Hemorrhoids • Diverticulosis • Diverticulitis • Constipation

  19. Epidemiological studies have shown that the incidence of colon cancer is lower in populations that consume diets high in fiber.

  20. Sources of Fiber

  21. Carbohydrate Metabolism • Primary role of CHO: glucose for energy • Fuels most of body’s cells • Preferred source for brain, nerve cells, and developing red blood cells • We need a constant supply!

  22. 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

  23. Carbohydrate Stores • We store glucose as glycogen in times of abundance • Liver storage • Condensation into glycogen • Hydrolysis for release of glucose when needed • Muscle • Hoards glycogen stores for use during exercise • Muscle glycogen not available to supplement blood glucose • If diet is insufficient, body converts other compounds • Making glucose from protein • Amino acid conversion • Gluconeogenesis

  24. CHO Intake and Ketogenesis • When CHO is inadequate, fat metabolism shifts • We make ketone bodies from fat fragments • Ketone body formation – starvation • Dulls hunger • Ketosis – acid-base balance • Acidifies blood • Minimum carbohydrate needs for protein sparing and prevention of ketosis: 50-100g/day • Varies based on metabolic rate and activity • In times of excess: glucose used to make fat

  25. Availability of Carbohydrates Determines Fatty Acid Metabolism

  26. 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 and glycemic load • Way of measuring effects on blood sugar of various foods

  27. The Constancy of Blood Glucose • Balancing within the normal range • Balanced meals at regular intervals • Diabetes mellitus • Insulin is either inadequate or ineffective • Type 1 diabetes • Type 2 diabetes • Hypoglycemia • Occurs most frequently in poorly managed diabetes

  28. Abnormal Blood Glucose: Diabetes Mellitus • Leading cause of blindness in the US • Accounts for 44% of all new cases of kidney failure • Gestational diabetes can occur in women during pregnancy • May increased risk of developing type 2 diabetes later in life

  29. Diabetes Symptoms and Complications • Immediate Symptoms: excessive thirst, frequent urination, excessive hunger • Long Term Complications: damage to the heart, blood vessels, kidneys, eyes and nervous system. • Infections are more common in patients with diabetes, and amputations may be necessary

  30. Diabetes Treatment • Goal: maintain blood glucose within normal range • Treatment involves diet, exercise, and sometimes meds • Refined CHO increasingly implicated in type 2 DM risk • Best way to reduce risk for type 2 DM: maintain healthy body weight

  31. Lactose Intolerance The enzyme lactase is needed to digest lactose, the sugar found in milk. If lactose is not digested in the small intestine, it passes through to the large intestine. Undigested lactose in the small intestine can cause cramping, abdominal distention and diarrhea.

  32. Lactose Intolerance • Lactase activity • Highest immediately after birth • Declines with age • Symptoms of intolerance • Prevalence • Genetically determined • Worldwide ~70% • US ~25%

  33. Lactose Intolerance • Dietary adjustments • Manage dairy consumption rather than restriction (for some people) • Probiotic bacteria can ease symptoms, aid in digestion • Fermented milk products often better tolerated • Response is highly individual • Potential nutrient deficiencies? • Riboflavin, vitamin D, and calcium • We can get these from other foods

  34. Health Effects of Sugars • Pleasure in moderate amounts • In excess: potential nutrient deficiencies and increased risk of chronic disease • Energy with few other nutrients • Best limited to discretionary kcal • Honey • More energy per spoonful than table sugar, but twice as sweet • Health benefits • Sugar sources: concentrated vs. dilute

  35. Recommended Intakes of Sugars • Dietary Guidelines • Choose and prepare foods with little added sugar • DRI (from USDA) • Added sugars • No more than 25% of day’s total energy • Impact on other food groups • WHO recommendations: no more than 10%!

  36. 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

  37. Health Effects of CHO • Heart disease • Whole grains • Slow release of sugars into blood • Phytochemicals - antioxidant effects • Soluble fibers • Help to eliminate cholesterol • Improving heart disease risk factors

  38. Health Effects of CHO • Diabetes • High-fiber foods • Quantity and quality of CHO foods • GI health • High-fiber foods • Ample fluids • Weight management • High-fiber foods and whole grains • Feeling of fullness

  39. Health Effects of CHO • Cancer • Dietary fiber and colon cancer • Fiber supplements vs. food sources • Sources of dietary fiber - what are they? • Phytochemicals • Preventing colon cancer • Diluting, binding, and removing cancer-causing agents • Bacterial fermentation—SCFA

  40. Health Effects of CHO • Excessive fiber - usually due to supplementation • Insufficient energy or nutrient needs (fullness) • Abdominal discomfort, gas, diarrhea • GI obstruction • Impaired nutrient absorption • Dietary goals for CHO • Balance, moderation, variety

  41. From Guidelines to Groceries • Read food labels • Total carbohydrate • Sugars • Fiber • Sugars • Added vs. natural sugars - how can we tell? • Grain products (bread, crackers, etc.) • Hidden refined ingredients • What to look for

  42. A sugar by any other name… • Agave nectar • Brown sugar • Cane crystals • Cane sugar • Corn sweetener • Corn syrup • Crystalline fructose • Dextrose • Evaporated cane juice • Fructose • Fruit juice concentrates • Glucose • High-fructose corn syrup • Honey • Invert sugar • Lactose • Maltose • Malt syrup • Molasses • Raw sugar • Sucrose • Sugar • Syrup

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