The Lipids: Triglycerides, Phospholipids, and Sterols

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

2. Introduction • Poor health from fat consumption is seen when a person consumes either • Too much fat • Too little fat • Too much of some kinds of fat • Lipids = Fat • Family of lipids • Triglycerides (TG) (fats & oils)* • Phospholipids • Sterols

3. Chemist’s View of Fatty Acids and Triglycerides • Lipids = • TG, Phosolipids, and sterols • Composed of C, H, and O • Have more C & H = supply more E per gram • Most are TG w/ glycerol backbones and three fatty acids (f.a.)

4. Chemist’s View of Fatty Acids and Triglycerides • F.A. vary in C chain lengths, degree of unsaturation, and # of double bonds (d.b.) • Trans-fatty acids

5. Chemist’s View of Fatty Acids and Triglycerides • Preview of lipids • Triglycerides: glycerol and 3 fatty acids • Fatty acids: even number of carbons • 4-24Cs; 18C most common in foods • Saturated or unsaturated • Mono or polyunsaturated

6. Chemist’s View of Fatty Acids and Triglycerides • Fatty acids • Organic acid • Methyl group (CH3) at one end; acid group (COOH) at other • Usually even number of Cs • Saturation

7. Chemist’s View of Fatty Acids and Triglycerides • Unsaturated • Monounsaturated f.a. : • Lack 2H atoms & have 1 d.b. • When most of the f.a.s are monounsat its called a monounsaturated fat • Polyunsaturated f.a.s (PUFA) • Lack 4 or more Hs & have at least 2 or more d.b. • When most of the f.a.s are polyunsaturated its called a polyunsaturated fat

8. Chemist’s View of Fatty Acids Location of d.b. • Nearest the methyl end of the carbon chain • Assigned an Omega number • Omega- 3-polyunsat f.a. • Linolenic acid are essential f.a. • Soybean and canola oils, flaxseed, walnuts • Omega- 6-polyunsat f.a. • Linoleic acids are essential f.a. • Vegetable, i.e. sunflower, safflower, corn, and soy bean oils • Monounsaturated fatty acids • Omega-9 groups • Oleic acid most predominate in diet • Olive, canola oils

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

10. Chemist’s View of Fatty Acids and Triglycerides pg 137

11. Chemist’s View of Fatty Acids and Triglycerides • Degree of unsaturation • Firmness • Polyunsaturated fats • Saturated fats • Length of carbon chain • Stability • Sat fat is more resistant to oxidation • monounsat fat is slightly less susceptible to spoilage • Polyunsat fat spoils most readily • Protection from rancidity:

12. Chemist’s View of Fatty Acids and Triglycerides • Degree of unsaturation • Hydrogenation • Trans-fatty acids

13. Chemist’s View of Fatty Acids and Triglycerides

14. Chemist’s View of Fatty Acids and Triglycerides

15. Chemist’s View of Phospholipids and Sterols • Phospholipids • Contain glycerol, 2 f.a. and a phosphate group with a molecule of choline • Solubility in fat and water • Emulsifiers in food industry • Roles

16. Chemist’s View of Phospholipids and Sterols • Sterols • Food sources • Cholesterol • Plant sterols • Roles of sterols • Starting material for bile acids, sex hormones, adrenal hormones, and vit. D • Structural component of cell membranes • Liver produces 800-1500mg cholesterol per day • Atherosclerosis

17. Lipid Digestion • Fats are hydrophobic • Tend to separate from watery fluids in GI tract • Digestive enzymes are hydrophilic • Goal of fat digestion • Dismantle triglycerides for body to absorb and use

19. Lipid Digestion • Mouth • Lingual lipase released by salivary glands • Stomach • Strong muscle contractions disperse fat into smaller droplets • Fat then exposed to Gastric lipase

20. Lipid Digestion • Small intestine • Cholecystokinin (CCK) • Pancreatic and intestinal enzymes • Phospholipids are hydrolyzed • Sterols are absorbed • Bile routes • Enterohepatic circulation • Soluble fibers are effective • in trapping some bile and • excreting it from the body thru the large intestine

21. Emulsification of Fat by Bile

22. Hydrolysis of a Triglyceride

23. Enterohepatic Circulation of Bile

24. Lipid Absorption • Directly into bloodstream • Glycerol and short- & medium-chain fatty acids diffuse and are re-absorbed directly into the bloodstream • Lymphatic system • Larger molecules, Monoglycerides and long-chain f.a.s, form micelles that get reabsorbed, and are reformed into new triglycerides. With protein they are transported by chylomicrons • When packaged with protein it’s then transported so that cells all over body may select needed lipids

25. Lipid Transport • Lipid transport is made possible by a group of vehicles known as lipoproteins • Four main types of lipoproteins • Chylomicrons • Very-low-density lipoproteins (VLDL) • Low-density lipoproteins (LDL) • High-density lipoproteins (HDL)

27. Health implications • High LDL is associated with higher risk of heart attack and is known as a “bad” cholesterol • High HDL seems to have a protective effect and is known as “good” cholesterol • Factors that lower LDL and raise HDL • Genes influence lipopro activity

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

29. Essential Fatty Acids • Linoleic acid – Omega-6 fatty acid • Linolenic acid – Omega-3 fatty acid • EPA & DHA-important for eyes, brain, and heart • Fatty acid deficiencies • Rare in US and Canada • Occur in infants and children with fat-free or low-fat diets

30. A Preview of Lipid Metabolism • Adipose cells store fat after meals • Lipoprotein lipase • Triglycerides reassembled inside adipose cells • Using fat for energy • Hormone-sensitive lipase inside the adipose cells hydrolyzes TG when needed for E • During fasting the body metabolizes fat, but requires CHO and pro for complete fat breakdown • Ketone bodies can be made from fat fragments

31. Health Effects of Lipids • Heart disease • Elevated blood cholesterol • Saturated fat • Dietary choices • Trans-fats • Dietary cholesterol

32. 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

33. Health Effects of Lipids • Cancer • Promotion rather than initiation of cancer • Dietary fat and cancer risk • Obesity • Cutting fat from diet reduces kcalories

34. 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

35. From Guidelines to Groceries • Very lean and lean options of meat and meat alternative products • Fat-free and low-fat milk products • Wide variety of vegetables, fruits, and whole grains • Avoid invisible fat from high-fat cheese, baked & fried goods • Choose wisely from many available food products

36. From Guidelines to Groceries • Fat replacers • Ingredients derived from CHO, pro, or fat • Replace fat in foods • Artificial fats offer sensory and cooking qualities but no kcalories. • Research on olestra supports its safety but it decreases the absorption of fat-soluble vits and may cause digestive distress in some • Read food labels • Total fat, saturated fat, trans fat, and cholesterol • Compare products • % Daily Value vs. % kcalories from fat