© 2011 Pearson Education, Inc. 5 Lipids: Essential Energy-Supplying Nutrients

© 2011 Pearson Education, Inc. What Are Lipids? Lipids Diverse group of molecules that are insoluble in water Fats The lipid content of diets and foods

© 2011 Pearson Education, Inc. What Are Lipids? Three types of lipids are found in foods and in body cells and tissues: Triglycerides Phospholipids Sterols

© 2011 Pearson Education, Inc. Triglycerides Triglycerides (triacylglycerides) contain: Three fatty acid molecules One glycerol molecule

© 2011 Pearson Education, Inc. Triglycerides Fatty acids are classified by: Carbon chain length Saturation level Shape

© 2011 Pearson Education, Inc. Triglycerides: Chain Length Short-, medium-, or long-chain fatty acids Carbons can be numbered Carboxyl end (COOH):  -carbon (alpha—first) Methyl end (CH 3 ): Ω-carbon (omega—last) Determines method of lipid digestion, absorption, metabolism, and use

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Triglycerides: Saturation Saturated fatty acids have hydrogen atoms surrounding every carbon in the chain Monounsaturated fatty acids lack one hydrogen atom (one double bond) Polyunsaturated fatty acids have more than one double bond

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Triglycerides: Shape Determined by the saturation of the carbon chains Saturated fatty acids pack tightly together and are solid at room temperature Animal fats, butter, and lard are high in saturated fatty acids

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Triglycerides: Shape Unsaturated fatty acids do not stack together well and are more liquid at room temperature Hydrogen atoms at the unsaturated part can be arranged in different positions: Cis: same side of the carbon chain Trans: opposite sides of the chain

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Triglycerides Hydrogenation: hydrogen atoms are added to unsaturated fatty acids Make oils more solid and more saturated Create trans fatty acids Reduce oxidation; resist rancidity Increase risk of cardiovascular disease

© 2011 Pearson Education, Inc. Triglycerides Essential fatty acids: cannot be made by the body and must be obtained from food Linoleic acid (omega-6 fatty acid) Found in vegetable and nut oils Alpha-linolenic acid (omega-3 fatty acid) Found in vegetables, soy, flaxseeds, walnuts

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Triglycerides Omega-3 fatty acids found in fish and fish oil Eicosapentaenoic acid (EPA) Docosahexaenoic acid (DHA) Reduce risk of heart disease Stimulate prostaglandins and thromboxanes that reduce inflammatory responses Reduce blood clotting and plasma triglycerides

© 2011 Pearson Education, Inc. Phospholipids Phospholipids contain Glycerol backbone, two fatty acids, phosphate Soluble in water Transport fat in the bloodstream Manufactured in our bodies (not required)

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Sterols Sterols contain multiple rings of carbon atoms Plant sterols appear to block the absorption of dietary cholesterol Cholesterol is made in our bodies and therefore is not necessary in the diet Sex hormones, vitamin D, bile

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Digestion of Fats Fat digestion begins in the small intestine Cholecystokinin (CCK) and secretin: gallbladder contractions release bile Bile is produced by the liver and stored in the gallbladder Bile emulsifies fat into small droplets Pancreatic enzymes break fat into two fatty acids and a monoglyceride Fat Digestion

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Absorption of Fats Lipoprotein transports lipids for absorption Chylomicron: lipoprotein produced in intestine to transport lipids from a meal Composed of fatty acids surrounded by phospholipids and proteins Soluble in water

© 2011 Pearson Education, Inc. Absorption of Fats Chylomicrons are absorbed by cells of the small intestine, then: Travel through the lymphatic system Transferred to the bloodstream Short- and medium-chain fatty acids are absorbed more quickly since they are not arranged into chylomicrons

© 2011 Pearson Education, Inc. Absorption of Fats Triglycerides in the chylomicrons must be disassembled by lipoprotein lipase before they can enter body cells In body cells, triglycerides can be: Used immediately for energy Used to make lipid-containing compounds Stored in muscle and adipose tissues Lipid Absorption

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The Roles of Fat 9 kcal per gram Major fuel at rest Endurance exercise Stored energy Essential fatty acids Fat-soluble vitamins Regulates cell function Maintains membrane Protects the body Provides flavors and textures of foods Helps us feel satiated

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How Much Fat? Acceptable Macronutrient Distribution Range (AMDR) for fat: 20−35% of calories Minimize saturated and trans fatty acid intake to lower risk of heart disease Active people may need more energy from carbohydrates and can reduce their fat intake to 20−25% of total calories

© 2011 Pearson Education, Inc. How Much Fat? Dietary Reference Intakes (DRIs) set for essential fatty acids Linoleic acid: AMDR of 5−10% of energy Alpha-linolenic acid: 0.6−1.2% of energy 5:1 to 10:1 ratio of linolenic:alpha-linolenic acid Saturated fat: less than 7% of energy Trans fats: reduced to the absolute minimum

© 2011 Pearson Education, Inc. Food Sources of Fat Visible fats Fats we add to foods Butter, cream, mayonnaise, salad dressings Invisible fats Fats hidden within foods Occur naturally or added during processing Baked goods, dairy, meats, fast foods

© 2011 Pearson Education, Inc. Food Sources of Fat Beneficial fats Omega-3 fatty acids may be low in diets Fish, walnuts, soy, canola, flaxseed Switching to more healthful fats without increasing total fat intake Use olive or canola oil in place of butter or margarine Select low-fat or nonfat dairy products

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Food Sources of Fat Fat replacers Used to lower fat content of foods Found in chips, cakes, cookies May cause GI side effects in large amounts Example: olestra (Olean) Fats in Food

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Cardiovascular Disease Cardiovascular disease Dysfunction of the heart or blood vessels Can result in heart attack or stroke

© 2011 Pearson Education, Inc. Cardiovascular Disease Risk factors for cardiovascular disease: Being overweight Physical inactivity Smoking High blood pressure Diabetes mellitus Inflammation

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Cardiovascular Disease Dietary fats increase blood lipids Highly saturated and trans fat intakes increase blood cholesterol Omega-3 fatty acids reduce inflammation and blood triglycerides

© 2011 Pearson Education, Inc. Cardiovascular Disease Blood lipids include: Chylomicrons—present only after a meal Very-low-density lipoproteins (VLDL) Low-density lipoproteins (LDL) High-density lipoproteins (HDL) Lipoproteins: VLDL, LDL, and HDL

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Cardiovascular Disease Diets high in saturated fats Decrease the removal of LDLs from the blood Increase blood cholesterol levels Contribute to the formation of plaques that can block arteries

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Cardiovascular Disease Diets high in trans fatty acids: Can raise blood levels of LDL-cholesterol as much as saturated fat Are abundant in hydrogenated vegetable oils (margarine, baked goods, fried foods) FDA requires that trans fatty acid content be listed on labels for conventional foods and some dietary supplements

© 2011 Pearson Education, Inc. Cardiovascular Disease Lifestyle changes can prevent or reduce cardiovascular heart disease Total fat intake: 20−35% total calories Saturated fat: less than 7% total calories Cholesterol: less than 300 mg per day Trans fat: reduce to absolute minimum Increase omega-3 fatty acids Dietary fiber: 20−30 grams per day Folate: 400 micrograms/day

© 2011 Pearson Education, Inc. Cardiovascular Disease Lifestyle changes can prevent or reduce cardiovascular heart disease Maintain normal blood glucose level Eat throughout the day No more than 2 alcoholic beverages per day for men and 1 drink per day for women Maintain an active lifestyle Maintain a healthful body weight Decrease salt intake (DASH diet) Fast Food Trends

© 2011 Pearson Education, Inc. Cardiovascular Disease Medicines help reduce risk Endogenous cholesterol synthesis inhibitors: statins Bile acid sequestrants Nicotinic acid