Lipids: Essential Energy-Supplying Nutrients

1. 5 Lipids: Essential Energy-Supplying Nutrients

2. What Are Lipids? • Lipids • Diverse group of molecules that are insoluble in water • Fats • The lipid content of diets and foods

3. What Are Lipids? • Three types of lipids are found in foods and in body cells and tissues: • Triglycerides • Phospholipids • Sterols

4. Triglycerides • Triglycerides (triacylglycerides) contain: • Three fatty acid molecules • One glycerol molecule

5. Triglycerides • Fatty acids are classified by: • Carbon chain length • Saturation level • Shape

6. Triglycerides: Chain Length • Short-, medium-, or long-chain fatty acids • Carbons can be numbered • Carboxyl end (COOH): -carbon (alpha—first) • Methyl end (CH3): Ω-carbon (omega—last) • Determines method of lipid digestion, absorption, metabolism, and use

8. Triglycerides: Saturation • Saturatedfatty 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

10. 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

12. 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

14. 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

15. 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

18. 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

19. Phospholipids • Phospholipids contain • Glycerol backbone, two fatty acids, phosphate • Soluble in water • Transport fat in the bloodstream • Manufactured in our bodies (not required)

21. Sterols • Sterolscontain 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

23. 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

25. 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

26. 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

27. 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

32. 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

34. 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

35. 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

36. 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

37. 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

40. 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

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

43. Cardiovascular Disease • Risk factors for cardiovascular disease: • Being overweight • Physical inactivity • Smoking • High blood pressure • Diabetes mellitus • Inflammation

45. 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

46. 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

48. 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