copyright © 2011 delmar, cengage learning. all rights reserved. chapter 5 lipids, or fats
TRANSCRIPT
Copyright © 2011 Delmar, Cengage Learning. ALL RIGHTS RESERVED.
Chapter 5
Lipids, or Fats
Copyright © 2011 Delmar, Cengage Learning. ALL RIGHTS RESERVED.
Objectives
• State functions of fats in body
• Identify sources of dietary fats
• Explain common classifications of fats
• Describe disease conditions with which excessive use of fats are associated
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Facts
• Fats– Belong to group of organic compounds
• Lipids
– Greasy substances
– Insoluble in water
• Each gram of fat contains 9 calories
• Composed of carbon, hydrogen, and oxygen– Lower proportion of oxygen than carbohydrates
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Functions
• Provide energy
• Carry fat-soluble vitamins
• Supply essential fatty acids
• Protect and support organs and bones
• Insulate from cold
• Provide satiety after meals
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Food Sources
• Animal– Fatty meats and fish
– Dairy products
– Egg yolks
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Food Sources
• Plant– Cooking oils and margarine
– Nuts
– Avocados
– Coconut
– Cocoa butter
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Visible and Invisible Fats
• Visible– Fats in foods that are
purchased and used as fats
– E.g., butter, margarine, lard, cooking oils
• Invisible– Fats not immediately
noticeable
– E.g., egg yolks, cheese, cream, salad dressings
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Stop and Share
• Consider the following scenario:– You are the nurse teaching a class about nutrition. A client
asks about ways to decrease the amount of fat in his diet. What are some suggestions you can offer him?
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Stop and Share
• Beware of hidden fats
• Decrease amount of fatty meats– E.g., bacon, sausage, luncheon meats
– Use lean meats, instead
• Use low-fat or skim milk
• Use egg whites instead of yolks when possible– Egg white contains no fat
• Almost entirely protein and water
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Classification
• Triglycerides– Most lipids in body
• 95 percent
– Composed of three fatty acids attached to framework of glycerol
• Phospholipids
• Sterols– Cholesterol
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Fatty Acid Classification
• May be classified by body’s need for them:– Essential fatty acids (EFAs)
– Nonessential
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Fatty Acid Classification
• May be classified by degree of saturation with hydrogen atoms:– Saturated
– Unsaturated• Monounsaturated
• Polyunsaturated
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Essential Fatty Acids
• Cannot be synthesized by body
• Must be obtained from diet
• Two families:– Omega-3
– Omega-6
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Nonessential Fatty Acids
• Can be synthesized by body
• Omega-9 fatty acids can be synthesized in body when EFAs present– Previously thought to be essential
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Saturated Fats
• Each of its carbon atoms carries all hydrogen atoms possible
• In general, animal foods contain more saturated fatty acids than unsaturated
• Usually solid at room temperature
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Saturated Fats
• E.g., meat, poultry, egg yolks, whole milk, whole milk cheeses, cream, ice cream, butter, chocolate, coconut, palm oil
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Monounsaturated Fats
• Have one place among carbon atoms where there are fewer hydrogen atoms attached than in saturated fats
• Lower low-density lipoprotein (LDL or “bad” cholesterol) when they replace saturated fat in one’s diet
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Monounsaturated Fats
• E.g., olive oil, canola oil, avocados, cashew nuts
• Recommend 15 percent of total daily calories
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Polyunsaturated Fats
• Have two or more places among carbon atoms where there are fewer hydrogen atoms attached than in saturated fats
• E.g., cooking oils made from sunflower, safflower, sesame seeds, corn, or soybeans; soft margarines with liquid vegetable oil as major ingredient; fish
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Polyunsaturated Fats
• Foods containing high proportions of polyunsaturated fats– Usually soft or oily
• Omega-3– Lower risk of heart disease
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Polyunsaturated Fats
• Omega-6– Lower cholesterol
• Recommend 8 percent or less of total daily calories
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Trans Fatty Acids (TFAs)
• Produced when hydrogen atoms added to monounsaturated or polyunsaturated fats to produce semi-solid product– E.g., margarine, shortening
• Raise LDL and total cholesterol
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TFAs
• Major sources:– Baked goods
– Restaurant foods
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Hydrogenated Fats
• Polyunsaturated vegetable oils to which hydrogen has been added commercially to make them solid at room temperature
• Hydrogenation– Process that turns polyunsaturated vegetable oils into
saturated fats
– E.g., margarine, shortening
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Cholesterol
• Sterol– Fatlike substance
• Exists in animal foods and body cells
• Does not exist in plant foods
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Cholesterol
• Essential for synthesis of bile, sex hormones, cortisone, and vitamin D
• Needed by every cell in body, but manufactured by liver
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Stop and Share
• Consider the following scenario:– Your client has been diagnosed with a high cholesterol
level greater than 200 mg per dL. Answer the following questions:
• What risks are associated with a high cholesterol level?
• What can be done to lower a high cholesterol level?
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Stop and Share
• High cholesterol leads to atherosclerosis– Cardiovascular disease in which plaque forms on inside of
artery walls• Plaque
– Fatty deposits containing cholesterol and other substances
– Can lead to heart attacks and strokes
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Stop and Share
• Reduce amount of total fat, saturated fats, and cholesterol
• Increase monounsaturated fats, lose weight, and exercise
• Increase consumption of soluble dietary fiber
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Stop and Share
• Do not exceed daily cholesterol intake of 300 mg
• In some cases, have medication prescribed
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Digestion and Absorption
• 95 percent of ingested fats digested
• Chemical digestion of fats occurs mainly in small intestine
• No digestion of fats occurs in mouth
• Slight digestion in stomach where gastric lipase acts on emulsified fats
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Digestion and Absorption
• Digestion in small intestine– Bile emulsifies fats
– Lipase reduces fats to fatty acids and glycerol
– Absorption occurs through villi of small intestine
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Lipoproteins
• Bile joins with products of fat digestion to carry fat
• Protein combines with final products of fat digestion to form lipoproteins
• Lipoproteins carry fat in blood to body cells
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Lipoproteins
• Classified according to mobility and density
• Types:– Chylomicrons
– Very-low-density lipoproteins (VLDLs)
– LDLs
– High-density lipoproteins (HDLs)
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Chylomicron
• First lipoprotein identified after eating
• Largest lipoprotein– Yet lightest in weight
• Composed of 80 to 90 percent triglycerides
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VLDLs
• Made by liver to transport lipids throughout body
• Composed of 55 to 65 percent triglycerides
• Carry triglycerides and other lipids to all cells
• As VLDL lose triglycerides, pick up cholesterol from other lipoproteins in blood– Become LDL
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LDLs
• Composed of 45 percent cholesterol with few triglycerides
• Carry most of blood cholesterol from liver to cells
• Level greater than 130 mg per dL– Considered to contribute to atherosclerosis
• “Bad” cholesterol
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HDLs
• Carry cholesterol from cells to liver for eventual excretion
• Level of 60 mg per dL or more– Considered to reduce risk of heart disease
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HDLs
• Increase by doing the following:– Exercising
– Maintaining desirable weight
– Giving up smoking
• “Good” cholesterol
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Metabolism and Elimination
• Liver controls fat metabolism
• In cells, fatty acids broken down to carbon dioxide and water– Releasing energy
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Metabolism and Elimination
• Excess fat stored as adipose tissue
• Carbon dioxide and water removed from body by circulatory, respiratory, and excretory systems
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Stop and Share
• Consider the following scenario:– Your client asks you about a new dietary supplement that
advertisers claim provides essential nutrients and lowers cholesterol “naturally.” How do you advise your client?
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Stop and Share
• Any new dietary supplement with nutritional claim should be evaluated carefully
• If item not included in Recommended Daily Allowance (RDA) or DRI, assume medical research has not determined it essential
• Ingestion of dietary supplements of unknown value could be damaging to one’s health
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Phospholipid
• Found in both plant and animal foods
• Synthesized in liver
• Natural emulsifier that helps transport fat in bloodstream
• E.g., lecithin
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Fat Alternatives
• Olestra– Made from carbohydrates and fat
– FDA approved for use in snack food
– Food labels must indicate that it “inhibits absorption of some vitamins and other nutrients”
– Should be used in moderation
– Contains no calories
– Can cause cramps and diarrhea
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Fat Alternatives
• Simplesse– Made from egg white or milk protein
– Can be used only in cold foods
– Not available for home use
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Fat Alternatives
• Oatrim– Carbohydrate-based
• Derived from oat fiber
– Can be used in baking• But not frying
– Provides calories• But less than fat
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Dietary Requirements
• Deficiency symptoms occur when fats provide less than 10 percent of total daily calories
• Food and Nutrition Board’s Committee on Diet and Health recommends that people reduce fat intake to 30 percent of total calories
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Dietary Requirements
• American Heart Association’s newest recommendation:– Consume ≤ 7 percent of saturated fats, 8 percent
polyunsaturated fats, and 15 percent monounsaturated fats
• At present, 36 percent of calories in U.S. diets derived from fats
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Conclusion
• Fats provide energy, carry essential fatty acids and fat-soluble vitamins, protect organs and bones, insulate from cold, and provide satiety after meals
• Fats are composed of carbon, hydrogen, and oxygen– Found in both animal and plant foods
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Conclusion
• Each gram of fat provides 9 calories
• Digestion occurs primarily in small intestines
• Excess of fat in diet can result in obesity, heart disease, or cancer