The Lipids: Triglycerides, Phospholipids, and Sterols

1. The Lipids: Triglycerides, Phospholipids, and Sterols Chapter 5

2. Introduction • Poor health • Too much fat • Too little fat • Too much of some kinds of fat • Family of lipids • Triglycerides • Phospholipids • Sterols

3. Chemist’s View of Fatty Acids and Triglycerides • Energy provided per gram • More carbons and hydrogens • Preview of lipids • Triglycerides: glycerol and 3 fatty acids • Fatty acids: even number of carbons • Fatty acids: saturated or unsaturated • Omega-3 and omega-6 fatty acids

4. Chemist’s View of Fatty Acids and Triglycerides • Fatty acids • Organic acid • Methyl group at one end; acid group at other end • Usually even number of carbons • 18-carbon fatty acids abundant in food • Saturations • Saturated – full of hydrogens • Unsaturated – missing hydrogens

5. Chemist’s View of Fatty Acids and Triglycerides • Fatty acids • Location of double bonds • Nearest the methyl end of the carbon chain • Omega number • Linolenic acid • Monounsaturated fatty acids • Omega-9 groups

6. Chemist’s View of Fatty Acids and Triglycerides • Triglycerides • Glycerol backbone • Three fatty acids • Formed via series of condensation reactions • Usually contain mixture of fatty acids

7. Chemist’s View of Fatty Acids and Triglycerides

8. Chemist’s View of Fatty Acids and Triglycerides

9. Chemist’s View of Fatty Acids and Triglycerides • Degree of unsaturation • Firmness • Polyunsaturated fats • Saturated fats • Length of carbon chain • Stability • Oxidation and spoilage of fats

10. Chemist’s View of Fatty Acids and Triglycerides • Degree of unsaturation • Hydrogenation • Advantages • Trans-fatty acids • Configurations – cis and trans • Similarity to other types of fat

11. Chemist’s View of Fatty Acids and Triglycerides

12. Chemist’s View of Fatty Acids and Triglycerides

13. Chemist’s View of Phospholipids and Sterols • Phospholipids • Solubility in fat and water • Emulsifiers in food industry • Lecithin • Food sources • Roles • Part of cell membranes • Emulsifiers

14. Chemist’s View of Phospholipids and Sterols • Sterols • Food sources • Cholesterol • Plant sterols • Roles of sterols • Body compounds made from cholesterol

15. Lipid Digestion • Fats are hydrophobic • Digestive enzymes are hydrophilic • Goal of fat digestion • Dismantle triglycerides • Monoglycerides, fatty acids, and glycerol

16. Lipid Digestion

17. Lipid Digestion • Mouth • Lingual lipase • Stomach • Strong muscle contractions • Gastric lipase

18. Lipid Digestion • Small intestine • Cholecystokinin (CCK) • Gall bladder releases bile • Bile acts as emulsifier • Pancreatic lipase • Hydrolysis • Triglycerides and phospholipids • Bile routes • Blood cholesterol levels

19. Emulsification of Fat by Bile

20. Enzyme Fat Fat Watery GI juices Bile Emulsified fat Emulsified fat Enzymes Emulsified fat In the stomach, the fat and watery GI juices tend to separate. The enzymes in the GI juices can’t get at the fat. When fat enters the small intestine, the gallbladder secretes bile. Bile has an affinity for both fat and water, so it can bring the fat into the water. Bile’s emulsifying action converts large fat globules into small droplets that repel each other. After emulsification, more fat is exposed to the enzymes, making fat digestion more efficient. Stepped Art Fig. 5-14, p. 143

21. Hydrolysis of a Triglyceride

22. Enterohepatic Circulation of Bile

23. In the gallbladder, bile is stored. In the liver, bile is made from cholesterol. In the small intestine, bile emulsifies fats. Bile reabsorbed into the blood In the colon, bile that has been trapped by soluble fibers is lost in feces. Stepped Art Fig. 5-16, p. 144

24. Lipid Absorption • Directly into bloodstream • Glycerol and short- & medium-chain fatty acids • Lymphatic system • Micelles diffuse into intestinal cells • Reassembly of triglycerides • Packed with proteins – chylomicrons • Bypass liver at first

25. Absorption of Fat

26. Lipid Transport • Four main types of lipoproteins • Chylomicrons • Largest and least dense • Transport diet-derived lipids • Liver removes remnants from blood • Very-low-density lipoproteins (VLDL) • Made in the liver • Proportion of lipid shift

27. Lipid Transport • Four main types of lipoproteins • Low-density lipoproteins (LDL) • Cell needs • Liver regulation • High-density lipoproteins (HDL) • Remove cholesterol from cells • Carry cholesterol to liver for recycling • Anti-inflammatory properties • Health implications

28. Lipid Transport

29. Role of Triglycerides • Provide the cells with energy • 9 kcalories per gram • Virtually unlimited ability to store fat energy in body • Adipose tissue • Secretes hormones • Adipokines • Skin insulation, shock absorption, cell membranes, and cell signaling pathways

30. Essential Fatty Acids • Linoleic acid – Omega-6 fatty acid • Sources • Linolenic acid – Omega-3 fatty acid • Sources • DHA • EPA • Eicosanoids • Fatty acid deficiencies

31. A Preview of Lipid Metabolism • Adipose cells store fat after meals • Lipoprotein lipase • Hydrolyzes triglycerides • Triglycerides reassembled inside adipose cells • Using fat for energy • Protein sparing • Energy deprivation • Fasting and ketone bodies

32. Health Effects of Lipids • Heart disease • Elevated blood cholesterol • Saturated fat – increase LDL cholesterol, promote blood clotting • Dietary choices • Trans-fats – increase LDL cholesterol • Dietary cholesterol

33. Health Effects of Lipids • Heart disease • Monounsaturated fats • Replace saturated and trans fats • Reduces blood cholesterol • Dietary sources • Omega-3 fats • Benefits • Dietary sources • Omega-6 to omega-3 ratio

34. Health Effects of Lipids • Cancer • Promotion rather than initiation of cancer • Dietary fat and cancer risk • Differs for various types of cancer • Obesity • Cutting fat from diet reduces kcalories • Dietary recommendations

35. Recommended Intakes of Fat • DRI and Dietary Guidelines • Diet low in saturated and trans fat • Diet low in cholesterol • 20 to 35 percent of daily energy from fat • AI set for linoleic and linolenic acids • Daily Values (DV) on food labels • Saturated fat and cholesterol • Risk of insufficient fat intake

36. From Guidelines to Groceries • Fat-soluble vitamins • A, D, E, and K • Flavor, texture, and palatability • Meats and meat alternatives • Selections • Milk and milk products • Selections

37. From Guidelines to Groceries • Vegetables, fruits, and grains • Lowers consumption of various fats in the diet • Invisible fat • Fried and baked goods • Choose wisely • Unprocessed foods

38. From Guidelines to Groceries • Fat replacers • Types • Risks • Read food labels • Total fat, saturated fat, trans fat, and cholesterol • Compare products • % Daily Value vs. % kcalories from fat

39. Butter and Margarine Labels Compared

40. Highlight 5 High-Fat Foods – Friend or Foe?

41. Guidelines for Fat Intake • Limit saturated fat and trans fat intake • Moderate kcalories • Enough fat for good health • Not too much of the harmful fats • DRI recommendations • Compatible with low rates of disease

42. High-Fat Foods and Heart Health • Olive oil • Benefits for heart health • Replace saturated fats • Nuts • LDL cholesterol • Fat composition • Benefits for heart health • Cautious advice for dietary inclusion

43. High-Fat Foods and Heart Health • Fish • Omega-3 fatty acids • Benefits for heart health • Environmental contaminants • Dietary recommendations

44. High-Fat Foods and Heart Health

45. High-Fat Foods and Heart Disease • Saturated fat and LDL cholesterol • Sources of saturated fat in the U.S. • Meats • Whole milk products • Tropical oils • Zero saturated fat is not possible • Trans fat • Limit hydrogenated foods

46. High-Fat Foods and Heart Disease

47. High-Fat Foods and Heart Disease

48. High-Fat Foods and Heart Disease

49. The Mediterranean Diet • Traditionally • Low in saturated fat • Very low in trans fat • Rich in unsaturated fat • Rich in complex carbohydrate and fiber • Rich in nutrients and phytochemicals • Benefits for heart disease risk