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Nutrition and Metabolism
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  1. Nutrition and Metabolism

  2. Critical Thinking Question:Why does your body need food? Answer: Food has two main functions: • Food provides raw materials for cells to build new molecules for growth and reproduction • Food provides energy

  3. Nutrients • Many cells of the body (ex. liver cells) can convert one molecule into another based on what is needed • Essential nutrients: must be provided by the diet because they can’t be created through conversions

  4. Nutrient: substance used by the body for growth, maintenance, and repair • Categories of nutrients: • Carbohydrates • Lipids • Proteins • Vitamins • Minerals • Water Nutrition

  5. Major Nutrients

  6. Most are derived from plants • Sugars (fruits) and starches (vegetables) • Exceptions: lactose from milk and small amounts of glycogens from meats Dietary Sources of Carbohydrates

  7. Preferred source (esp. glucose) to produce cellular energy (ATP) • Examples: neurons and red blood cells Body Uses of Carbohydrates

  8. Dietary Requirements of Carbohydrates • 125-175 grams/day (mainly complex carbohydrates) • Complex carbohydrates – bread, cereal, rice, potatoes • “Strive for Five” – servings of fruits and vegetables per day

  9. Excesses: Obesity Nutritional deficits (“empty calories”) Gastrointestinal problems (constipation) Deficits: Tissue wasting (muscle breakdown) Metabolic acidosis (fat breakdown) Dietary Requirements of Carbohydrates

  10. Saturated fats from animal products (meat and dairy) • Unsaturated fats from nuts, seeds, and vegetable oils • Cholesterol from egg yolk, meats, and milk products Dietary Sources of Lipids

  11. Trans fats • “Healthy” vegetable oils that have been “hydrogenated” to make them more solid • Used in many snack and junk foods • Increases shelf life of foods (they don’t get rancid) • Have the most negative effect on cholesterol – raises the bad, lowers the good

  12. Help body absorb fat-soluble vitamins • Major energy fuel for liver cells and skeletal muscle • Main component of ALL cell membranes • Adipose tissue protects organs, provides insulation, and stores energy • Cholesterol is necessary to make hormones and bile Body Uses of Lipids

  13. 30% or less of total caloric intake • Saturated fats should be less than 10% of total calories • Cholesterol should be less than 250 mg (ex. one egg yolk) Dietary Requirements of Lipids

  14. Excesses: Obesity Increased risk of cardiovascular disease Deficits: Weight loss Difficulty with temperature regulation Poor growth/repair Dietary Requirements of Lipids

  15. Fat Substitutes • Modified starches or proteins • Some are metabolized, but some are not because they cannot be absorbed • Drawbacks: • Typically don’t stand up to heat for frying • Don’t taste the same as real fat • May cause GI disturbances (ex. diarrhea) • May interfere with the absorption of fat-soluble drugs and vitamins

  16. Most complete proteins come from animal products (eggs, milk, meat) • Complete proteins: contain all essential amino acids • Legumes (beans and peas), nuts, leafy greens also have proteins, but are incomplete • Incomplete proteins: missing or low in one or more of the essential amino acids Dietary Sources of Proteins

  17. Major component of structural materials (skin, nails, muscles) • Regulate chemical reactions (enzymes) Body Uses of Proteins

  18. Depends on age, size, and metabolic rate • 0.8 grams per kilogram of body weight • General conversion – divide weight in pounds by 3 to equal the number of grams needed Dietary Requirements of Proteins

  19. Excesses: Obesity Aggravation of chronic disease Deficits: Profound weight loss and tissue wasting Poor growth/repair Anemia Dietary Requirements of Proteins

  20. Most vitamins are used as coenzymes, helping enzymes with their chemical reactions • Most must be ingested – the body can only make Vitamins A, B, D, and K Vitamins

  21. Two main categories: • Water-soluble: absorbed with water, not stored in the body, excreted in the urine if not used • Fat-soluble: absorbed with fats, stored in the body, excesses can lead to toxicity Vitamins

  22. Body requires moderate amounts of 7 minerals (Ca, P, K, S, Na, Cl, Mg) and trace amounts of about 12 others • Make up 4% of the body weight, mostly due to Ca and P in bones • Provide strength to certain structures Minerals

  23. Vital components to many biological compounds (ex. iron (Fe) in hemoglobin) • Important electrolytes (sodium/chloride ions) • Found in mostly vegetables, legumes, milk, and meats Minerals

  24. Definition: all chemical reactions necessary to maintain life • Catabolism – substances are broken down to simpler substances • Energy (ATP) is released from food during a catabolic process called cellular respiration Metabolism

  25. 2) Anabolism – larger molecules are built from smaller ones • Tissue growth and repair • Storage molecules (ex. glycogen) Metabolism

  26. Three Major Stages of Metabolism Stage 1: • Occurs in the digestive tract • Absorbed nutrients are transported to cells through the blood

  27. Three Major Stages of Metabolism Stage 2: • Occurs in the cytoplasm of body cells a) Nutrients are built into cellular molecules (anabolism) b) Nutrients are broken down into ATP without oxygen (catabolism) a.k.a. GLYCOLYSIS

  28. Three Major Stages of Metabolism Stage 3: • Occurs in the mitochondria of body cells • Nutrients are broken down into ATP (catabolism) in the presence of oxygen a.k.a. CELLULAR RESPIRATION

  29. Cellular Respiration • Series of reactions that breaks down food molecules to create ATP • Must occur in a series of steps or else energy would be released as a blast of energy • ATP is the ONLY energy cells can directly use • Cells release carbon dioxide (CO2) and water (H2O) as a result of the reactions

  30. General Equation for Cellular Respiration

  31. Cellular Respiration • Two separate pathways, BOTH start with GLYCOLYSIS (NO OXYGEN NEEDED) • Glycolysis is the first step, but only extracts 10% of energy from glucose – only 2 ATP per reaction! • Remaining 90% of energy is still locked in an intermediate molecule (pyruvic acid) made from glucose

  32. Cellular Respiration Presence or lack of oxygen determines the next step: 1) To continue WITHOUT OXYGEN (Anaerobic): Lactic Acid Fermentation 2) To continue WITH OXYGEN (Aerobic): Cellular Respiration

  33. Lactic Acid Fermentation • Glycolysis can make ATP really fast, but if there is no oxygen, it proceeds to lactic acid fermentation • In muscle cells, lactic acid builds up and then is removed by blood to the liver (i.e. muscle soreness after vigorous exercise) • In the liver, it will be converted to a useable energy molecule when oxygen is available

  34. Cellular Respiration • When oxygen is available, glucose is further broken down in the mitochondria to make ATP • Slightly longer process, but yields almost 20x the amount of ATP as glycolysis • Remaining 90% of energy is released by two steps: 1) Krebs cycle 2) Electron Transport Chain (ETC)

  35. Metabolic Pathways Involved in Cellular Respiration Figure 14.17

  36. ATP: The Totals • Without oxygen: the cell can produce only 2 ATP molecules during glycolysis • With oxygen: the cell can produce 36 more ATP in the Krebs cycle and ETC Final Total: 38 ATP from 1 glucose • Cellular respiration extracts 38% of energy from glucose – the rest is lost as ???

  37. Why settle for only 38%? Answer: If glucose were burned directly in air, 100% of the energy would be in the form of heat and light, which the human body cannot use. So, 38% is actually pretty efficient!!

  38. Metabolism of Specific Nutrients

  39. Carbohydrate Metabolism • Most carbohydrates are eventually transformed to glucose to create ATP through cellular respiration • Too much glucose (supply > demand) leads to glycogenesis • Glycogenesis: conversion of glucose to glycogen to be stored in the liver and skeletal muscles • Too little glucose (supply < demand) leads to glycogenolysis • Glycogenolysis: glycogen stored in the liver is converted back to glucose and released into the blood

  40. Fats make up 78% of energy reserves • Broken down into fatty acids and glycerol which go through various stages in cellular respiration to make ATP • Body cells remove fat and cholesterol to build membranes and steroid hormones • Excess fatty acids and glycerol are converted to triglycerides through lipogenesis Fat Metabolism

  41. Cholesterol and fatty acids cannot freely circulate in the bloodstream • They are transported by lipoproteins (lipid-protein complexes) made by the liver • Low-density lipoproteins (LDLs) transport from liver to body cells (“bad” cholesterol) • High-density lipoproteins (HDLs) transport from body cells to the liver (“good” cholesterol) Fat Metabolism: Cholesterol Transport

  42. You need very little cholesterol in your diet because most of the cholesterol that your body needs is made in the liver! FACT

  43. Ingested proteins are broken down to amino acids • Cells remove amino acids to build proteins (cell structures and enzymes) • Excess amino acids are used for energy or converted into fat for storage • Amino acids are used to make ATP only when proteins are overabundant or there is a shortage of other sources Protein Metabolism

  44. Amine groups are removed from proteins as ammonia • The rest of the protein molecule enters the Krebs cycle in mitochondria • The liver converts harmful ammonia to urea which can be eliminated in urine Protein Metabolism: Production of ATP from Proteins

  45. Catabolic-Anabolic Steady State of the Body ABSORPTIVE STATE: • During and shortly after eating • Focus is ANABOLISM and ENERGY STORAGE

  46. Catabolic-Anabolic Steady State of the Body POST-ABSORPTIVE STATE: • When the GI tract is empty • Focus is CATABOLISM and FUEL REPLACEMENT IN BLOOD

  47. Question: What are the roles of the liver in metabolism? Answers: Several roles in digestion (bile) Detoxifies drugs and alcohol Produce cholesterol, blood proteins (albumin and clotting proteins) Gluconeogenesis: glucose is produced from fats and proteins

  48. Critical Thinking Question: How does the body increase blood glucose levels without ingesting additional food? Answer: Glycogenolysis and gluconeogenesis!

  49. Energy and Exercise Quick energy: • Stored ATP – 10 seconds of energy • Lactic Acid Fermentation – 90 seconds of energy • This creates an oxygen debt - heavy breathing is required to get rid of lactic acid build up

  50. Energy and Exercise Long term energy: • Cellular Respiration - breaks down glycogen, which has enough stored for 15-20 minutes of constant activity • After 20 minutes, when body runs out of glycogen, it breaks down fat • Pacing is necessary because cell respiration releases energy more slowly than the other processes