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Transcript
Chapter 16 Nutrition: The Basis of Healthy Living 16-1 Digestion Digestion: The breakdown of food into substances small enough to be absorbed from the digestive tract Nutrition: The science of diet and health Nutrient: Chemical substance in food that provides energy and raw materials required by chemical reaction Monosaccharides Digestion Proteins Amino acids Digestion Fats Glycerol + fatty acids Carbohydrates Digestion Small molecules produced may undergo (1) Complete breakdown to produce energy, CO2, and H2O; (2) Recycling into new biomolecules; or (3) Placement into storage as triglycerides (fat) for future use The Release and Use of Chemical Energy in the Breakdown and Synthesis Of Biomolecules 16-2 Sugar and Polysaccharides: Digestible and Indigestible Digestible carbohydrates: • Simple sugars – glucose and fructose • Disaccharides – sucrose, maltose, & lactose • Polysaccharides – amylose and amylopectin in starch from plants, & glycogen from meat. Digestion: • In mouth: enzyme α-amylase breaks glycogen into smaller polysaccharides. • In acidic stomach: further digestion. • In small intestine: debranching enzyme & β-amylase break down remaining polysaccharides to glucose. • Glucose (major fuel molecule) transported across the intestinal lining into bloodstream. Indigestible carbohydrates (dietary fiber): • Cellulose and its derivatives (insoluble) • Pectin (the substance that makes jam and jelly gel, soluble) • Plant gums (soluble) Health benefits of fiber: decreases constipation & blood cholesterol levels, may prevent colorectal cancer 16-3 Lipids: Mostly Fats and Oils • Triglycerides in fat cells hydrolyzed to give glycerol & free fatty acids • Transported to liver • Fatty acids broken down to 2-carbon molecular fragments that enter main energy-producing pathway Recommended dietary fat content: 20% - 35% of daily calories Today’s diet: 40% saturated, 40% monounsaturated, & 20% polyunsaturated High saturated fat and cholesterol leads to atherosclerosis Cholesterol is transported in the bloodstream by lipoproteins (clusters of lipids, cholesterol, & watersoluble proteins); water soluble because of their many NH3+ and COO− ions on proteins. Low-density lipoproteins (LDLs): ~65% of blood cholesterol; “bad” cholesterol; distributes cholesterol to arteries, where it can form the deposits of atherosclerosis High-density lipoproteins (HDLs): ~ 25%; “good” cholesterol; transports excess cholesterol from body tissues to the liver, where it is converted to bile acids that are needed in digestion. 16-4 Proteins in the Diet Dietary proteins provide amino acids for new protein synthesis and N for synthesis of other kinds of N-containing biomolecules Cooking → denatures proteins (first step of digestion) Stomach: proteins → polypeptides Small intenstine: polypeptides → amino acids Excess amino acids not stored in body, so need to eat some protein every day. 16-5 Vitamins in the Diet Vitamin: organic compound essential to health that must be supplied in small amount by diet • • • • Don’t provide energy Aren’t digested Can’t be synthesized by body Needed by body to function as coenzymes Coenzyme: A non-protein molecule that makes enzyme function possible Fat soluble – A, D, E, K Water soluble – B, C Test Your Knowledge Which of the following is the body’s major fuel molecule? A) LDL Cholesterol B) Glycine C) Glucose D) Vitamin C 16-5a Fat Soluble Vitamins Vitamin A, D, E, and K stored in fatty tissues; nonpolar hydrocarbon chains. Want enough stored; but too much is toxic Vitamin A: essential to vision; prevention of infection Vitamin D: UV light converts steroid to vitamin D; lack of exposure to sunlight leads to vitamin D deficiencies Vitamin E: antioxidant; found distributed among fats in nature Vitamin K: involved in blood clotting; overdoses are dangerous so need a prescription; given to newborns 16-5b Water Soluble Vitamins Vitamins B & C: Have polar groups: -OH, -NH2, -COOH; Not stored; must be consumed regularly B-vitamins: B6, B12, folic acid, niacin, thiamin, riboflavin, biotin, panthothenic acid Vitamin B6 (“master vitamin”): involved in 60 enzymatic reactions, many involving metabolism and synthesis of proteins Niacin deficiency common in countries with corn-based diet. Folic acid: should be taken before conception; can reduce risks of birth defects (spina bifida) Enriched flour contains riboflavin, thiamin, niacin, folic acid (and iron) Vitamin C Vitamin C • Anti-oxidant • Helps destroy invading bacteria • Prevents the entrance of viruses into cells • Combats effects of drugs and pollutants • Aids in synthesis of collagen (in cartilage, bone, tendons) • Important in healing wounds for infants and pregnant women Prevent the common cold? More evidence in favor of its ability to decrease the severity of cold symptoms than for any ability to prevent colds Diets low in vitamin C result in scurvy, characterized in its early stages by lack of energy, and which can ultimately result in death Test Your Knowledge For which of the following vitamins could an overdose be a great concern? A) Vitamin A B) Vitamin B C) Vitamin C D) RIboflavin 16-6 Minerals in the Diet • Elements other than C, H, N, and O that are needed for good health • Mostly present in foods, supplements, and our bodies in their ionic state (e.g. Ca2+, not Ca; Na+ not Na) • Many excreted daily and so need daily replenishment Seven macronutrients: Make up 4% of body weight 1. Ca 2. Mg 3. Na 4. K 5. Cl 6. P 7. S Micronutrients: 1. Fe: deficiency causes anemia 2. Cu 3. Zn: deficiency causes poor growth and development; poor wound healing 4. I: Essential for thyroid gland function 5. Se 6. Mn 7. F 8. Cr 9. Mo The Macrominerals Test Your Knowledge Which of the following is considered a macronutrient? A) B) C) D) Copper Iodine Iron Phosphorous 16-7 Food Additives Food additives with little/no nutritional value; added to processed food 16-7a The GRAS List GRAS: Generally recognized as safe • 100s of substances • Published in 1959 and 1960 • Compiled from questionnaire asking experts in nutrition & toxicology to give opinions about the safety of additives. • Since publication, some substances have been removed (suspicion that they are cancer-causing) e.g. sweetener cyclamate, which was correlated with an increase in bladder cancer • FDA must approve new items for list based on test results 16-7b Food Preservation Preservatives: additive that prevents the growth of microorganisms or slows the oxidation process Other approaches: drying, salting, sugared solution Prevents multiplication of microorganisms during shelf life of food. Food is spoiled by toxic substances secreted by the microorganisms. Sometimes preferred because sterilization by heat or radiation, or freezing, may affect the quality of the food Two common chemical preservatives (both are esters): • Sodium benzoate (nonalcoholic beverages, fruit juices, fountain syrups, margarines, pickles, relishes, olives, salads, pie fillings, jams, jellies, and preserves) • Sodium propionate (bread, chocolate products, cheese, pie crust, and fillings) 16-7c Antioxidants Action of O2 in the air is the chief cause of the destruction of the fats in food Antioxidants (reducing agents): molecules able to donate an electron to a free radical before it can do any damage. BHA and BHT donate a H● from their OH groups. 16-7d Sequestrants Cu, Fe, Ni, and their ions catalyze the oxidation of fats. Trace amounts of metals are in food from soil or harvesting or manufacturing machinery Sequestrant: molecule that ties up a metal atoms or ions by forming bonds with them The Na and Ca salts of ethylenediaminetetraacetic acid (EDTA) are common sequestrants Metal atom is bound here 16-7efg Food Flavors, Enhancers and Color • Food flavors (most originally derived from plants e.g. peppermint oil) • Flavor enhancers: no taste but enhance other flavors (e.g. MSG, 5’-nucleotides, and maltol) • Food colors: some from lab, some from nature • Large organic molecules with several double bonds and aromatic rings • β carotene: example of a natural food color that may be noted on ingredient list as “artificial color.” • Synthetic food colors must be tested by FDA to ensure safety, quality, consistency, and strength of color Other Food Additives •pH control: • Weak acids added to give acidic taste or to mask aftertaste • Buffers added to resist changes to pH • e.g. Citric Acid • Anticaking agents: prevent caking in humidity (e.g. MgSiO3) • Stabilizers and thickeners: improve texture • Mostly polysaccharides (e.g. guar gum) • OH groups form H-bonds with H2O and help to provide a more even blend of water and oils throughout the food Test Your Knowledge Which of the following food additives is paired correctly with its role? A) Guar Gum – Anticaking agent B) EDTA – flavor enhancer C) BHA – antioxidant D) MSG – food preservative 16-8 Energy: Use It or Store It Basal metabolic rate (BMR): The minimum energy required to sustain an awake but resting body • Affected by body weight and activity level Energy from Foods Fats: 9 kcal/g; 9 Cal/g Carbohydrates: 4 kcal/g; 4 Cal/g Proteins: 4 kcal/g; 4 Cal/g Food Calorie (Cal) =1000 calories (cal) = 1 kilocalorie (kcal). Energy taken in (food) = Energy used + Energy stored (fat) Test Your Knowledge What kind of molecule will provide the most energy per gram? A) Fats B) Carbohydrates C)Proteins D)Vitamins Approximate Percentages of Carbohydrates, Fats, Proteins, and Water in Some Whole Foods 16-9 Our Daily Diet The percentage of daily values on a label (the DVs) are based on a 2000-Cal daily diet 16-10 Some Daily Diet Arithmetic A moderately active 100 lb. woman would get 30% of her daily 1750 food Calories by consuming 53 g of fat per day. How many cookies can she eat and leave 33 g of fat for other foods to be eaten that day? (Their nutrition label says that there are two cookies per serving and 45 Cal from fat per serving.) What percentage of her 53 g of fat will the cookies provide? To leave 33 g of fat: 53 g fat − 33 g fat = 20 g fat from cookies can be eaten With 9 Cal/gram of fat, the grams of fat per “serving” of two cookies is 45 Cal 1g 5g fat × = 2 cookies 9 Cal 2 cookies 2 cookies 20 g fat × = 8 cookies 5 g fat 20g fat × 100 = 38% 53 g fat Test Your Knowledge Estimate the daily caloric needs of a 150 lb freshman who runs 3 miles at least 5 days a week and plays racquetball once or twice a week. The estimated BMR is 150 lb × 10 kcal/lb = 1500 kcal = 1500 food Calories The activity level is moderate. Therefore, using the factor of 1.6 from Table 16.4, the estimated daily caloric needs are 1500 kcal × 1.6 = 2400 kcal = 2400 food Calories