History. Aron first proposed that fat may be essential for normal growth Tested on animals-vitamins A,D,E added. Fat deficiency severely affected

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1 Chapter 5 LIPIDS

3 History 1918 Aron first proposed that fat may be essential for normal growth Tested on animals-vitamins A,D,E added Fat deficiency severely affected Bone growth Reproduction Called Vitamin F essential substance contained in fat

4 History 1929 Burr Nutritional importance of specific lipids in fat Fat free diet given to rats led to impaired growth Scaly skin Tail necrosis Increased mortality Symptoms reversed with linoleic acid Coined term essential fatty acids (EFA)

5 Lipids Characteristics Do not readily dissolve in water Solid at room temperature Oils are liquids Triglycerides storage form Energy dense (9 kcal /gm) Types of lipids: Triglycerides Phospholipids Sterols (Cholesterol)

6 Triglycerides Triacylglycerols Largest proportion of dietary lipids consumed Composed of 3 fatty acids (FA) Glycerol molecule TG vary in the type of FA and their bonding pattern Oils Generally unbranched hydrocarbon chains Even number of carbons (4-25 C atoms) FA vary in the number and arrangement of double bonds

7 Fatty Acid Structure H H H H H H H H H H H H H H H H H O H-C--C--C--C--C--C--C--C--C--C--C--C--C--C--C--C--C-C-OH H H H H H H H H H H H H H H H H H omega end degree of saturation alpha end

8 Saturated Fatty Acid Structure H H H H H H H H H H H H H H H H H O H-C--C--C--C--C--C--C--C--C--C--C--C--C--C--C--C--C-C-OH H H H H H H H H H H H H H H H H H omega end alpha end degree of saturation: single carbon bond

9 Monounsaturated Fatty Acid Structure H H H H H H H H H H H H H H H O H-C--C--C--C--C--C--C--C--C=C--C--C--C--C--C--C--C--C-OH H H H H H H H H H H H H H H H H H omega end One double bond alpha end

10 Polyunsaturated Fatty Acid Structure H H H H H H H H H H H H H O H-C--C--C--C--C--C=C--C--C=C--C--C--C--C--C--C--C--C-OH H H H H H H H H H H H H H H H H H omega end > 2 double bonds alpha end

11 Essential Fatty Acids Location of double bond Omega-3 fatty acid (alpha-linolenic acid) Omega-6 fatty acid (linoleic acid) Body can only make double bonds after the 9th carbon from the omega end Functions Immune function, vision, cell membrane, and production of hormone-like compounds

12 Essential Fatty Acids Omega-3 Omega 6 Alpha-linolenic acid Linolenic acid DHA EPA (docosahexanoic (eicosapentaenoic acid) acid) Arachidonic Acid

13 Essential Fatty Acids DHA, EPA Decrease blood clotting Not with anticoagulant medication Having surgery Reduce heart attacks Decrease inflammation, pain Too much hemorrhagic stroke Other possible uses: Lower triglycerides, rheumatoid arthritis, Arachidonic Acid Increases blood clotting Increases inflammatory response

14 Triglycerides Form of fat in foods Form of fat in body structures Some FA transported in bloodstream attached to proteins Most FA formed into TG by body

15 Trans Fat Bonds the result of hydrogenation Increases viscosity of oils High melting point Cis form has H on same side as double bond Processing H transferred to opposite side

16 Fig. 5.4

17 Phospholipids Small amount of dietary lipid in form of PL Contain polar head groups Hydrophilic head Hydrophobic tail (two FA chains)

18 Phospholipids Built on a glycerol backbone Contains phosphorus compound(s) Found in body Synthesized by the body as needed Not needed in diet

19 Fig

20 Functions of Phospholipids Component of cell membrane Emulsifier Bile acids Lecithins Improves food products Found in wheat germ, peanuts, yolks, soy beans, organ meat

21 Emulsifiers

22 Sterols Multi-ringed structure Do not have a glycerol backbone Cholesterol is a sterol Waxy substance Do not readily dissolve in water Found in animal foods

23 Functions of Cholesterol Essential component of cell membrane Produced by the liver Found only in animal products Forms important hormones Estrogen, testosterone, vitamin D Precursor to bile acids

24 Fig

25 Lipids in Foods

26 Hidden Fat Look on the Nutrition Facts labels Look on the lists of ingredients Control portion size Reduced-Fat Foods Calorie content is about the same Sugar is commonly added in place of fat

27 Fat Substitutes Water Diet margarine Adding water, less fat per serving Z-trim Starch derivative that binds with water Fiber cellulose Luncheon meats, salad dressings, baked goods Few calories, half the amount of fat

28 Fat Substitutes Dairy-Lo Protein globules Feel like fat, no FA Used in baked goods, frostings, salad dressings 1-2 kcal/g Olestra or Olean (links fatty acid to sucrose) Engineered fat, not digested FDA approved for fried snack foods Fat-soluble vitamins bind with Side effects, abdominal cramping, loose stools (>20g)

29 Digestion of Fats and Oils Digestive process very specific Absorption through water-soluble environment Begins in mouth Lingual lipase-released from glands in tongue Starts hydrolysis (breakdown of TG to FFA) Chewing begins mechanical dispersion Enlarges surface area

30 Digestion of Fat in the Stomach Gastric lipase Activated by an acidic environment Acts on triglycerides containing short- & medium-chain fatty acids Fat entering duodenum is 70% TG + partially digested products

31 Digestion of Fat in the Small Intestine Primary site of fat digestion Bile salts Pancreatic lipase Presence of fat digestion products Causes release of hormone Cholecystokinin (CCK) from mucosa of upper intestine- Stimulates contraction of gallbladder Stimulates release of pancreatic lipase

32 Digestion of Fat in the Small Intestine Bile acid released Principal components Phospholipids, bile salts, phospholipids Fat is broken down To monoglycerides and fatty acids Bile emulsifies digested fat (suspends)

33 Digestion of Phospholipids Small portion of ingested lipid Secreted in large quantities in bile Enzymes released From pancreas phospholipase A 2 Broken down to Monoglycerides Fatty acids Glycerol

34 Digestion of Cholesterol Broken down into Free cholesterol, FFA Enzymes released From pancreas Cholesterol ester hydrolase Following digestion bile acids absorbed Returned to liver (98%), recycled Make bile acids

35 Absorption of Fat 95% of dietary fat is absorbed Passive diffusion into the absorptive cells Short- and medium-chain (<12 C) fatty acids Are water soluble Enter the portal system Long-chain fatty acids re-form into triglycerides Not water soluble Enter the lymphatic system

36 Carrying Fat in the Bloodstream Water (blood) and oil (fat) are incompatible Unique system of fat transportation is needed Aggregate (clump) of lipids and protein Lipoproteins Lipid portion Triglycerides Cholesterol, cholesterol esters Phospholipids Proteins Apolipoproteins-soluble

37 Transportation of Fats Following absorption by cells of small intestine Re-formed into triglycerides Int. cells package TG into chylomicrons Transported through lymph system Bloodstream Water soluble shell, chylomicrons

38 Transportation of Fats In bloodstream Lipoprotein lipase (blood vessel walls) Breaks down triglycerides in the chylomicrons (FA, glycerol) Fatty acids absorbed by cells Muscle cells use FA for fuel Adipose cells reform TG for storage Chylomicron remnant Delivered to the liver, recycled

39 Lipoproteins

40 Composition and Roles of Lipoproteins

41 Transportation of Synthesized Fat Made primarily by the liver Very-Low-Density Lipoprotein (VLDL) Low-Density Lipoprotein (LDL) High-Density Lipoprotein (HDL)

42 Very-Low-Density Lipoprotein Made by liver Mostly triglycerides, low in density Transported to tissues Energy source Structural component Converted back to TG Release of TG creates LDL

43 Low-Density Lipoprotein Primary function Transport cholesterol to tissues Provides building blocks for cell growth Cell membranes Synthesis of hormones High levels associated with increased risk of cardiovascular disease Oxidized LDL Preferentially taken up by scavenger receptors on macrophages

44 Scavenger Cells Scavenger WBC removes (oxidized) LDL from circulation Build-up of plaque on walls of the blood vessels Development of atherosclerosis Vessel damage caused by: Smoking, diabetes, hypertension, homocysteine, high LDL, infection

45 High-Density Lipoprotein (HDL) Synthesized by liver and intestine High proportion of protein Picks up cholesterol from dying cells and other sources Transfers cholesterol to other lipoproteins Transfers cholesterol directly back to the liver

46 Benefits of (a high) HDL (level) Removes cholesterol from the bloodstream HDL may block oxidation of LDL Reduces risk of cardiovascular disease Pre-menopausal women have higher HDL

47 Antioxidant Consuming fruits and vegetables Reduces oxidation Antioxidants for reduction of heart disease? No long term studies, yet

48 Functions of Essential Fatty Acids

49 Omega-3 Fatty Acid Primarily from fish oil Also found in canola, walnuts, flax seeds, mussels, crab, shrimp, and soybean oil Recommended intake of ~2 servings of fish per week

50 Omega-6 Fatty Acid Found in vegetable oils Only need ~ 2-4 tablespoons a day

51 Signs and Symptoms of Essential Fatty Acids Deficiency Flaky, itchy skin Diarrhea Infections Retarded growth and wound healing

52 Functions of Fatty Acids Provide energy Efficient storage of energy Insulation Protection Transport fat-soluble vitamins Some satiety Flavor and mouth feel

Fats and Other Lipids

Fats and Other Lipids Chapter 6 Chapter 6: Fats and other Lipids 1 6.1 Understanding Lipids Lipids include: 1. Fatty acids 2. Triglycerides 3. Phospholipids 4. Cholesterol Oil and Water Don t Mix Because