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Chapter 5 The Lipids: Fats, Oils, Phospholipids, and Sterols
Nutrition: Concepts & Controversies, 12e Sizer/Whitney
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Learning Objectives Discuss the reasons why a moderate intake of lipids is an essential part of a healthy diet. Compare and contrast the physical properties and the sources of saturated, polyunsaturated, and monounsaturated fats.
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Learning Objectives Describe how and where dietary lipids are broken down and absorbed during digestion and how they are transported throughout the body. Describe the significance of the blood tests for HDL and LDL cholesterol. Describe the roles of omega-3 and omega-6 fatty acids in the body, and discuss which may be too low in some people’s diets and how they can increase their intakes.
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Learning Objectives Justify the recommendation to eat fatty fish instead of relying on fish oil supplements, and discuss safety issues surrounding both choices. Describe the information and structure of a trans-fatty acid, and state ways in which consumers may reduce their intakes.
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Learning Objectives Develop a diet plan that provides enough of the right kinds of fats within calorie limits. Discuss evidence for the benefits and drawbacks of specific dietary fats in terms of their potential effects on human health.
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Introduction Diet moderate in fats Three classes of lipids
Lipids are necessary and valuable Lipids can harm health Three classes of lipids Triglycerides Phospholipids Sterols
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Usefulness of Fats in the Body
Chief storage form of energy Provides most energy for body’s work Adipose tissue Secretes hormones Purposes of fat Shock absorbers, insulation, cell membranes Fat-soluble substances
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A Fat Cell
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Lipids enter from blood
Muscle tissue Fat tissue Blood capillaries Fat cell Lipids enter from blood Figure 5-1 A Fat Cell Within the fat cell, lipid is stored in a droplet. This droplet can greatly enlarge, and the fat cell membrane will expand to accommodate its swollen contents. More about fat tissue (also called adipose tissue) and body functions in Chapter 9 Lipids exit to blood Cell membrane Nucleus Fig. 5.1, p. 151
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Usefulness of Fats in Food
People naturally like high-fat foods Aromas Flavors Tenderness Satiety
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Triglycerides: Fatty Acids and Glycerol
Glycerol backbone Three fatty acids Fatty acid differences Chain length Saturation Animal species make triglycerides
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A triglyceride formed from 1 glycol + 3 fatty acids
Glycerol Figure 5-3 Triglyceride Formation Glycerol, a small, water-soluble carbohydrate derivative, plus three fatty acids equals a triglyceride. A triglyceride formed from 1 glycol + 3 fatty acids 3 fatty acids of differing lengths Fig. 5.3, p. 153
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Saturated Versus Unsaturated Fatty Acids
Saturation Hydrogen atoms Levels of saturation Saturated Unsaturated Polyunsaturated Monounsaturated
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Three Types of Fatty Acids
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Points of unsaturation
Saturated Monounsaturated Polyunsaturated Point of unsaturation Points of unsaturation Figure 5-4 Three Types of Fatty Acids The more carbon atoms in a fatty acid, the longer it is. The more hydrogen atoms attached to those carbons, the more saturated the fatty acid is. Fig. 5.4, p. 154
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Saturated Versus Unsaturated Fatty Acids
Melting point More unsaturated, more liquid Fat hardness Softer generally is healthier Sources of fatty acids Heart disease
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Fatty Acid Composition of Common Food Fats
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Phospholipids and Sterols
Glycerol, two fatty acids, and a phosphorus molecule Soluble in water and fat Emulsifier Sterols Roles in the body Plant sterols
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Digestion and Absorption of Fats
Stomach Small intestine Bile Pancreas
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Watery digestive juices Bile compounds Enzyme
Fat Fat Watery digestive juices Bile compounds Enzyme Emulsified fat Emulsified fat Enzymes In the stomach, the fat and watery digestive juices tend to separate. Enzymes are in the water and can’t get at the fat. When fat enters the small intestine, the gallbladder secretes bile. Bile compounds have an affinity for both fat and water, so it can bring the fat into the water. Figure 5-6 The Action of Bile in Fat Digestion Detergents are emulsifiers and work the same way, which is why they are effective in removing grease spots from clothes. Molecule by molecule, the grease is dissolved out of the spot and suspended in the water, where it can be rinsed away. After emulsification, more fat is exposed to the enzymes, making fat digestion more efficient. Fig. 5.6, p. 157
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Digestion and Absorption of Fats
Fatty acids split from glycerol Fatty acids, phospholipids, and monoglycerides Bile shuttles lipids across mucus layer Efficiency of absorption process Speed of digestion
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The Process of Lipid Digestion and Absorption
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Esophagus Pancreas Liver Stomach Small intestine Large intestine
1 In the mouth and stomach: Little fat digestion takes place. 2 Small intestine 2 In the small intestine: Digestive enzymes accomplish most fat digestion in the small intestine. There, bile emulsifies fat, making it available for enzyme action. The enzymes cleave triglycerides into free fatty acids, glycerol, and monoglycerides. 3 Large intestine (colon) 4 3 At the intestinal lining: The parts are absorbed by intestinal villi. Glycerol and short-chain fatty acids enter directly into the bloodstream. Capillary network Lymph The cells of the intestinal lining convert large lipid fragments, such as monoglycerides and long-chain fatty acids back into triglycerides and combine them with protein, forming chylomicrons (a type of lipoprotein) that travel in the lymph vessels to the bloodstream. 4 Figure 5-7 The Process of Lipid Digestion and Absorption Villi Chylomicrons Blood vessels 5 In the large intestine: A small amount of cholesterol trapped in fiber exits with the feces Lymph to blood 5 Bloodstream Fig. 5.7, p. 158
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Transport of Fats Glycerol and shorter-chain fatty acids Larger lipids
Bloodstream Larger lipids Protein carriers Released into lymph Chylomicrons
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Storing and Using the Body’s Fat
Body conserves fat molecules Fat depots Excess carbohydrate Call for energy Dismantle stored triglycerides Release fatty acids into blood Carbohydrate’s role How to use more fat for energy…
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Glucose to Fat
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The fragments can provide immediate energy for the tissues.
Fatty acid Glucose is broken down into fragments. The fragments can provide immediate energy for the tissues. Or, if the tissues need no more energy, the fragments can be reassembled, not back to glucose but into fatty acid chains. Figure 5-8 Glucose to Fat Glucose can be used for energy, or it can be changed into fat and stored. Fig. 5.8, p. 159
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Dietary Fat, Cholesterol, and Health
Heart and artery disease Saturated and trans fats Beneficial fats Cancer Diet high in saturated fats Obesity Overconsumption of calories
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Recommendations for Lipid Intakes
Some fat in the diet is essential Healthy range of fat intakes DRI 20 to 35 percent of daily energy Fats to keep low Essential fatty acids
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Lipoproteins and Heart Disease Risk
Lipoprotein movement in the body Liver Types of lipoproteins Chylomicrons Very-low-density lipoproteins (VLDL) Low-density lipoproteins (LDL) High-density lipoproteins (HDL)
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Lipoproteins
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(More lipid, less protein) (Less lipid, more protein)
100 80 Protein 60 Percent 40 Cholesterol 20 Phospholipid Triglyceride Figure 5-9 Lipoproteins As the graph shows, the density of a lipoprotein is determined by its lipid-to-protein ratio. All lipoproteins contain protein, cholesterol, phospholipids, and triglycerides in varying amounts. An LDL has a high ratio of lipid to protein (about 80 percent lipid to 20 percent protein) and is especially high in cholesterol. An HDL has more protein relative to its lipid content (about equal parts lipid and protein). LDL (More lipid, less protein) HDL (Less lipid, more protein) Lower density Higher density Fig. 5.9, p. 162
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Phospholipid Protein Cholesterol Triglyceride A typical lipoprotein
Figure 5-9 Lipoproteins As the graph shows, the density of a lipoprotein is determined by its lipid-to-protein ratio. All lipoproteins contain protein, cholesterol, phospholipids, and triglycerides in varying amounts. An LDL has a high ratio of lipid to protein (about 80 percent lipid to 20 percent protein) and is especially high in cholesterol. An HDL has more protein relative to its lipid content (about equal parts lipid and protein). A typical lipoprotein Fig. 5.9, p. 162
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Lipoproteins and Heart Disease Risk
LDL and HDL difference Size and density Delivery and scavenging Inflammation Heart attack risk Oxidation of LDL Phytochemicals
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Food Cholesterol and Blood Cholesterol
Saturated and trans fats CVD risk indicators Dietary cholesterol Genetic inheritance Moderation is key
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Recommendations Applied
Heart disease Leading cause of death among Americans Lower LDL Dietary tactics Trim saturated and trans fats from diet Raise HDL Physical activity Benefits for heart health
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Food Fat, Saturated Fat, and Calories
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Top Contributors of Saturated Fats to the U.S. Diet
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The Need for Essential Fatty Acids
Linoleic acid and linolenic acid Functions Eicosanoids DRI recommendations Deficiencies
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Omega-6 and Omega-3 Fatty Acid Families
Linoleic Omega-6 fatty acid Arachidonic acid Linolenic acid Omega-3 fatty acid DHA and EPA Heart disease Brain function and vision Inflammation
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Fish Oil Intakes and Cardiovascular Death Rates
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Recommendations for Omega-3 Fatty Acid Intake
Competition for metabolic enzymes Consumption levels Lacking omega-3 fatty acids Fish oil supplements Health concerns with fish oil supplements Omega-3 enriched foods Flaxseed
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Food Sources of Omega-6 and Omega-3 Fatty Acids
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Seafood Safety – Balancing Risks and Benefits
Safe consumption levels Mercury Methylmercury Damage to the body Cooking methods of fish Benefits outweigh risks
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Mercury in Fish Species
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Effects of Processing on Unsaturated Fats
Hydrogenation Effects on fats Oxidation of unsaturated oils Hydrogenation of oils Benefits of hydrogenation Nutrient losses Alternatives to hydrogenation
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Hydrogenation Yields Both Saturated and Trans-Fatty Acids
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Unsaturated fatty acid
Points of unsaturation are places on fatty acid chains where hydrogen is missing. The bonds that would normally be occupied by hydrogen in a saturated fatty acid are shared, reluctantly, as a double bond between two carbons that both carry a slightly negative charge. Point of unsaturation Figure 5-14 Hydrogenation Yields Both Saturated and Trans-Fatty Acids When a positively charged hydrogen is made available to an unsaturated bond, it readily accepts the hydrogen and, in the process, becomes saturated. The fatty acid no longer has a point of unsaturation. Hydrogenated fatty acid (now fully saturated) Trans-fatty acid The hydrogenation process also produces some trans fatty acids. The trans fatty acid retains its double bond but takes a twist instead of becoming fully saturated. It resembles a saturated fatty acid both in shape and in its effects on health. Fig. 5.14, p. 172
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Effects of Processing on Unsaturated Fats
Trans-fatty acids Polyunsaturated fats Change in chemical structure Health effects LDL and HDL cholesterol Similarities with saturated fat Trans fat in foods
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Fat in the Diet Essential fat Visible vs. invisible fat Added fats
20% of calories from unsaturated fats Visible vs. invisible fat Added fats Majority are invisible fats
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Fat in the Diet Meat, poultry, fish, dried peas & beans, eggs, & nuts
Four categories for meat Limit intake to 5 to 7 ounces per day Choosing low-fat meats Ground turkey or chicken vs. beef Milk, yogurt, and cheese Foods not included in this category Grains
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Calories, Fat, and Saturated Fat in Cooked Ground Meat Patties
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Lipids in Milk, Yogurt, and Cheese
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Lipids in Bread, Cereal, Rice, and Pasta
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Defensive Dining Portion sizes In the grocery stores
Fat replacers & artificial fats Olestra “Fat-free” options Cooking at home
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Substitute Ingredients to Lower Saturated Fat Intakes
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Defensive Dining Use flavorful fats Choose unsaturated oils
Revamp recipes Suggestions Find lower-fat fast foods Change your habits
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Good Fats and Bad Fats – Which are Which?
Controversy 5
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Objectives to “Low-Fat” Guidelines
Problems with low-fat diets Groups who benefit from low-fat diets Mediterranean-type diets New guidelines Up to 35 percent of total calories
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High-Fat Foods and Heart Health
Olive oil Potential health benefits Darker the better (extra virgin) Canola oil
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High-Fat Foods and Heart Health
Mediterranean diet Whole foods Dietary focus Fish Nuts Walnuts Almonds Potential benefits
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High-Fat Foods and Heart Health
Butter or margarine Read labels Low saturated fat and trans fat levels Plant-enriched margarines Drawbacks Fats to avoid Choose carefully among high-fat foods
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Impact of Change in Saturated Fatty Acid Intake on Blood LDL Cholesterol and Heart Disease Risk
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