Dr. Mathews: Lecture Outline 1 CHAPTER 5 LIPIDS OVERVIEW This chapter describes the four classes of lipids: fatty acids, triglycerides, phospholipids, and sterols. The basic structure of fatty acids is described and essential fatty acids are discussed, including dietary recommendations and food sources. Current research related to omega-3 fatty acids is emphasized. Structure, functions, and roles in the body are part of the triglyceride presentation. The roles of phospholipids and sterols, particularly cholesterol, are mentioned. A description of where fat is found in foods is presented, including how to find hidden fats and how fat replacements are used. A general explanation of fat digestion and absorption is provided. Lipid transport is discussed including chylomicrons, and high-, low-, and very low-density lipoproteins. The roles fat, cholesterol, and lipoproteins play in the development or prevention of cardiovascular disease are discussed. Recommendations for fat intake are outlined including those from the American Heart Association, the National Cholesterol Education Program, and the Food and Nutrition Board. Dietary sources of total fat and various fatty acids are discussed. Brief additional discussions include the contribution of fat to satiety, flavor and texture of foods, fat rancidity, and medical interventions to lower blood lipids KEY TERMS Alpha-linolenic acid Antioxidant Arachidonic acid Atherosclerosis BHA and BHT Bile Cerebrovascular accident (CVA) Cholesterol Chylomicron Cis fatty acid Diastolic Blood Pressure Diglyceride Docosahexaenoic acid (DHA) Eicosapentaenoic acid (EPA) Emulsifier Essential fatty acids Glycerol Hemorrhagic stroke High-density lipoprotein (HDL) Homocysteine Hydrogenation Lecithin Linoleic acid Lipase Lipoprotein Lipoprotein lipase Long-chain fatty acid Low-density lipoprotein (LDL) Menopause Monoglyceride Monounsaturated fatty acid Myocardial infarction Oleic acid Omega-3 fatty acid Omega-6 fatty acid Oxidize Phospholipid Plaque Polyunsaturated fatty acid Rancid Saturated fatty acid Scavenger cells Sterol Systolic Blood Pressure Total parenteral nutrition Trans fatty acid Triglyceride Vegan Very low-density lipoprotein (VLDL) Dr. Mathews: Lecture Outline 2 LECTURE OUTLINE I. Lipids: common properties A. General needs 1. 2-4 tablespoons of plant oil 2. Fatty fish twice a week or soybean, canola, or walnut oil 3. Minimize saturated fat, cholesterol, and trans fat 4. Food and Nutrition Board suggests fat can be up to 35% of total calories B. Defining characteristics 1. Do not dissolve in water 2. Structures vary 3. Fats are solid at room temperature 4. Oils are liquid at room temperature 5. Chapter 5 will use the term fat to refer to all lipids II. Lipids: main types A. Fatty acids: the simplest form of lipids 1. General structure a. Chain of carbons bonded together and flanked by hydrogens b. The alpha end contains an acid c. The omega end is a methyl group d. Each fat in food is a mixture of many different fatty acids 2. Saturated fatty acids a. Each carbon in the chain is saturated by hydrogens [Fig 5-1 (a)] b. Solid at room temperature c. Mostly animal fats d. Saturated fats in milk are suspended in liquid 3. Unsaturated fatty acids a. Contain at least 1 double bond so at least 2 carbons are not saturated b. Monounsaturated fatty acids 1) One double bond 2) Canola and olive oils are high in monounsaturated fatty acids c. Polyunsaturated 1) Two or more double bonds 2) Corn, soybean, sunflower, and safflower oils are rich in polyunsaturated fatty acids d. Trans fatty acids 1) Hydrogens are positioned (naturally or synthetically) on opposite sides of the double bond in the fatty acid chain 2) Chain becomes straight, giving it characteristics like a saturated fat 4. Chain length affects fatty acid characteristics a. Most long-chain, saturated fats are solid at room temperature b. Monounsaturated fats, regardless of length, are liquid at room Dr. Mathews: Lecture Outline 3 temperature c. Most fats in the body and food are long chain 5. Location of the double bond affects fatty acid characteristics a. Omega-3 (?3) fatty acid 1) First double bond is 3 carbons from the methyl (omega) end 2) E.g., alpha-linolenic acid b. Omega-6 (?6) fatty acid 1) First double bond is 6 carbons from the methyl end 2) E.g., linoleic acid c. Omega-3 and Omega-6 are both essential fatty acids d. Omega-9 fatty acid 1) First double bond is 9 carbons from the methyl end 2) E.g., oleic acid B. Triglycerides 1. Most common fat/oil found in foods 2. Most fats in the body are triglycerides 3. Triglycerides are attached to proteins for transport 4. Structure a. Glycerol backbone with 3 fatty acids attached [Fig. 5-4 (a)] b. Monoglyceride has 1 fatty acid attached to the glycerol c. Diglyceride has 2 fatty acids attached to the glycerol 5. Most fats are absorbed as monoglycerides and free fatty acids C. Phospholipids 1. Glycerol backbone with two fatty acids and 1 compound containing phosphorous [Fig. 5-4 (b)] 2. Important part of cell membrane 3. Participate in fat digestion 4. Body is able to produce them 5. Lecithin is a phospholipid D. Sterols 1. Multi-ringed structure [Fig. 5-4 (c)] 2. Waxy substance that does not dissolve in water 3. Cholesterol is an example a. Incorporated into all cell structures b. Used to form some hormones and bile c. Body can make all the sterols it needs III. Fats and oils in food A. Fat percentages of various foods 1. Fat dense means more than 60% of kilocalories come from fat 2. Foods containing approximately 100% of energy as fat ate very energy dense a. Salad oils b. Butter Dr. Mathews: Lecture Outline 4 c. Margarine d. Mayonnaise 3. Foods containing approximately 80% fat a. Nuts b. Bologna c. Avocados d. Bacon 4. Foods containing approximately 75% fat a. Peanut butter b. Cheddar cheese 5. Foods containing approximately 40% to 60% fat a. Meats b. Whole dairy c. Doughnuts 6. Major lipids and food examples a. Saturated fatty acids: animal fats b. Unsaturated/essential fatty acids: plant oils c. Phospholipids: egg yolks, wheat germ, peanuts, soybeans, organ meats, and additives (e.g., lecithin) that function as emulsifiers d. Cholesterol: found only in animal foods B. Fat is hidden in some foods 1. Use the Nutrition Facts labels on food 2. Ingredients are listed by order of weight in the product 3. Look for fat, lard, nut oils, butter, cream, egg, and partially hydrogenated oils in the ingredients list 4. Low-fat means less than 3 grams of fat per serving 5. Fat-free means less than 0.5 grams fat per serving 6. Reduced-fat means 25% less fat than the reference food C. Fat in food provides some satiety, flavor, and texture 1. High-fat meals are high-calorie meals 2. Fat adds body, tenderness, and smooth texture to foods 3. Many flavorings dissolved in fat D. Wise use of reduced-fat foods is important 1. Calorie content of fat-reduced products is not usually less 2. Usually more sugar is added E. Fat replacement strategies for foods 1. Water, starch derivatives, and fibers a. Replace the body that fat provides b. Usually ˝ the kilocalories as fat c. Cannot use in frying 2. Protein-derived fat replacements a. 1-2 kilocalories per gram b. Give mouth feel like fat Dr. Mathews: Lecture Outline 5 3. Engineered fats and related products a. Olestra: fatty acids are synthetically bound to sucrose b. Cannot be digested by human enzymes or bacteria in gut c. Not absorbed d. Can be used for frying e. Binds fat-soluble vitamins, thus reducing absorption f. Warning label must say may cause GI disturbances 4. Fat rancidity limits shelf-life of foods a. Double bonds of unsaturated fats break down, producing disagreeable odor and flavor b. Breakdown of fats is driven by ultraviolet light, oxygen, some processing methods c. Saturated and trans fats are less susceptible to rancidity d. Methods used by food manufacturers to prolong shelf life 1) Use of partially hydrogenated (trans) fats 2) Addition of antioxidants (e.g., vitamin E, BHA, and BHT) 3) Air-tight seal 5. Hydrogenation of fatty acids in food production increases trans fatty acid content a. Benefits of solid fats in food production 1) Increased shelf life 2) Flavor and mouth feel (e.g., flaky pie crusts) b. Partial hydrogenation converts some double bonds into single bonds, making fats semi-solid at room temperature c. Cis fatty acids: hydrogens exist on the same side of the double bond, causing a bend in the carbon chain of the fatty acid d. Trans fatty acids: hydrogens exist on opposite sides of the double bond, leaving a straighter carbon chain that resembles a saturated fatty acids e. Trans fats are associated with negative health effects 1) Increase blood cholesterol 2) Increase inflammation f. FDA requires listing of trans fat content on food labels g. Dietary Guidelines for Americans recommends limiting trans fat intake h. Foods high in trans fats include some margarines, non-dairy creamers, deep-fried foods, and commercially-prepared baked goods IV. Making lipids available for body use A. Digestion 1. Stomach a. Lipase enzyme acts on triglycerides with fatty acids of shorter than usual chain length b. Action of this enzyme is minimal Dr. Mathews: Lecture Outline 6 2. Small intestine a. Lipase released from pancreas digests most triglycerides b. Triglycerides break into monoglycerides and fatty acids c. Bile, an emulsifier, is released from the gallbladder d. Bile suspends fats in the watery digestive juices so the enzymes can break them down B. Absorption 1. Fatty acids and monoglycerides diffuse into absorptive cells 2. Short- and medium-chain fatty acids (less than 12 carbons) travel through the portal vein to the liver 3. The more typical long-chain fatty acids reform triglycerides and enter circulation via the lymphatic system V. Carrying lipids in the bloodstream A. Since water and fat don't mix, fats must be specially packaged in lipoproteins to travel through the body B. Dietary fats are carried by chylomicrons 1. Intestinal cells package triglycerides into chylomicrons 2. Chylomicrons enter the lymphatic system 3. Like all lipoproteins, chylomicrons have a water-soluble shell made of phospholipids, cholesterol, and protein that contains a fat droplet of triglycerides 4. Chylomicrons are carried to the bloodstream 5. Lipoprotein lipase is an enzyme that is attached to the walls of the blood vessels; breaks down the triglycerides into glycerol and fatty acids 6. Cells in the immediate area absorb the fatty acids; glycerol goes back to the liver a. Adipose cells tend to store the fatty acids b. Muscle cells can use the fatty acids as immediate energy 7. Chylomicron remnants travel back to the liver and are repackaged into other lipoproteins and bile C. Other lipoproteins transport lipids from the liver to the body cells 1. Liver a. Takes up lipids from the blood b. Manufactures lipids and cholesterol c. Synthesizes lipoproteins and releases them into the blood 2. Very-low-density lipoproteins (VLDL) a. Rich in triglycerides so they are not dense b. Carry lipids made by liver to cells c. As fats are released, VLDL becomes more dense (LDL) 3. Low-density lipoproteins (LDL) a. Carry cholesterol made by liver and other sources to cells b. Provide body cells with cholesterol and protein required for cell growth Dr. Mathews: Lecture Outline 7 and synthesis of cell membranes and hormones 4. High-density lipoproteins (HDL) a. High proportion of protein to triglycerides makes it the most dense lipoprotein b. Produced by liver and intestine c. Contribute to removal of cholesterol from cells 5. "Good" and "bad" cholesterol in the bloodstream a. Cardiovascular disease risk increases with low HDL b. Women tend to have high HDL, especially before menopause c. If LDL is not cleared from the blood stream, it is taken up by scavenger cells (WBCs) in the arteries d. This leads to buildup of cholesterol in the blood vessels e. Diets low in saturated fat, trans fat, and cholesterol increase uptake of LDL by the liver, thus decreasing atherosclerosis VI. Essential functions of fatty acids A. The essential fatty acids 1. Need to consume only about 5% of our kilocalories as EFA (2 ? 4 tablespoons of plant oils) 2. Omega-3 fatty acids a. Alpha-linolenic acid found in canola and soy bean oils, crab, mussels, shrimp, walnuts, and flax seed b. Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) can be synthesized by the body from alpha-linolenic acid. Consuming EPA and DHA, which are found in fatty fish (e.g., salmon, tuna, sardines, anchovies, bass, catfish, herring, mackerel, trout, and halibut), decreases needs for alpha-linolenic acid c. Tend to decrease blood clotting d. Tend to decrease inflammatory processes e. Can lower triglycerides f. Too much omega-3 fatty acids can cause hemorrhagic stroke g. Recommended intake of alpha-linolenic acid 1) 1.6 grams per day for men 2) 1.1 grams per day for women 3. Omega-6 fatty acids a. Linoleic acid b. Arachidonic acid (can be synthesized by the body from linoleic acid) c. Increase clotting and immune processes B. Effects of a deficiency of essential fatty acids 1. Flaky itchy skin 2. Diarrhea 3. Infections 4. Seen in people on total parenteral nutrition with little fat for 2 ? 3 weeks Dr. Mathews: Lecture Outline 8 VII. Broader roles for fatty acids and triglycerides in the body A. Providing energy 1. Fatty acids are the main fuel for muscles at rest and during light activity 2. Come from triglycerides in diet and stored in adipose B. Storing energy for later use 1. Stored mainly as triglycerides 2. Storage is limitless 3. Energy dense: 9 kilocalories per gram 4. Adipose cells are 80% lipid and 20% water and protein C. Insulating and protecting the body D. Transporting fat-soluble vitamins 1. Aid in absorption of fat-soluble vitamins 2. Mineral oil cannot be digested; taking it at mealtimes decreases absorption of fat-soluble vitamins 3. Fat malabsorption can also cause deficiencies of some minerals VIII. Phospholipids in the body A. Its role as an emulsifier (bile) is important in fat digestion B. Form parts of cell membranes C. Made in liver IX. Cholesterol in the body A. Functions 1. Hormones 2. Building block of bile acids 3. Vitamin D 4. Cell membranes 5. Lipoproteins B. The liver makes what the body needs X. Recommendations for fat intake A. No RDA established for adults B. Dietary Guidelines for Americans recommends fat intake not exceed 20% - 35% of kilocalories C. For prevention of heart disease, American Heart Association recommends: 1. Limiting saturated fat intake to 7% of total kilocalories 2. Limiting trans fat intake to 1% of total kilocalories 3. Limiting cholesterol intake to 300 milligrams per day D. Food and Nutrition Board recommends 5% of kilocalories from EFA 1. Linoleic acid (omega-6) a. Men: 17 grams per day b. Women: 12 grams per day 2. Alpha-linolenic acid (omega-3) Dr. Mathews: Lecture Outline 9 a. Men: 1.6 grams per day b. Women: 1.1 grams per day E. Some dietary patterns are associated with reduced risk of heart disease 1. Mediterranean diet: main sources of fat are olive oil and fish oil with relatively little animal fat; also includes moderate alcohol, emphasis on whole grains, and increased physical activity 2. Dean Ornish diet: purely vegetarian diet that is very low in fat, emphasizes high-fiber carbohydrate choices, and increased physical activity XI. Nutrition and Your Health: Lipids and cardiovascular disease A. Introduction 1. Warning signs of a heart attack (myocardial infarction) 2. Statistics about coronary heart disease in the U.S. B. Development of cardiovascular disease 1. Occurs slowly; plaque buildup can begin in childhood 2. Associated with inadequate blood circulation from plaque buildup 3. Myocardial infarction (heart attack) a. Blood flow surrounding the heart is interrupted b. Irregular or cessation of heart beat 4. Cerebrovascular accident (CVA; stroke) a. Blood flow to part of the brain is interrupted b. Part of the brain may die 5. Atherosclerosis a. Development of plaque b. Plaque formation increases likelihood of clot formation c. 95% of all heart attacks are caused by these clots d. First develops to repair damage of a vessel lining that can be caused by smoking, diabetes, hypertension, high homocysteine levels, high LDL, or infections e. Usually occurs where artery branches f. Oxidized LDL contributes to plaque formation 1) Oxidized LDL is taken up by scavenger cells 2) Antioxidants in food (not supplements) can reduce oxidation of LDL and reduce plaque buildup 3) Current studies suggest that vitamin E supplementation may be helpful for prevention (not treatment ) of cardiovascular disease, but use should be monitored by a physician C. Risk factors for cardiovascular disease 1. Total cholesterol over 200 milligrams per 100 milliliters of blood 2. High LDL (> 130 mg/dl) 3. Smoking 4. Hypertension (BP > 139/89) 5. Diabetes Dr. Mathews: Lecture Outline 10 6. Other risk factors: a. Low HDL (<40 mg/dl) b. Age (> 55 years for women; > 45 years for men) c. Family history d. High fasting triglycerides (> 200 mg/dl) e. Obesity f. Inactivity 7. Inadequate intakes of vitamin B-6, folate and vitamin B-12 may lead to increased homocysteine levels, which damage blood vessels 8. Metabolic syndrome also raises risk D. Medical interventions to lower blood lipids 1. Medications a. Reduce production of cholesterol by liver b. Reduce absorption of bile acids from intestine c. Reduce triglyceride production by liver 2. Other possible medical therapies for cardiovascular disease a. Food products or pills containing plant stanols/sterols reduce cholesterol absorption in the small intestine b. Surgical procedures 1) Percutaneous transluminal coronary angioplasty involves use of a balloon catheter to break apart a blockage, usually followed by placement of a stent to hold the artery open 2) Coronary artery bypass graft involves removal of the blocked artery followed by grafting of a blood vessel from another part of the body (usually the leg) oem Dr. Mathews: Lecture Outline
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