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Chap. 6: Lipids

Chap. 6: Lipids. Properties of Lipids. Non-polar: water insoluble Energy density = Monomers: fatty acids & glycerol. LIPIDS: Classes. True fats: 95 % are triglycerides Fats: generic name, solid at room temp Oils: Phospholipids Sterols. omega end (methyl) alpha end (Carboxylic)

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Chap. 6: Lipids

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  1. Chap. 6: Lipids

  2. Properties of Lipids • Non-polar: water insoluble • Energy density = • Monomers: • fatty acids & glycerol

  3. LIPIDS: Classes • True fats: 95 % are triglycerides • Fats: generic name, solid at room temp • Oils: • Phospholipids • Sterols

  4. omega end (methyl) alpha end (Carboxylic) Hydrocarbon chain 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

  5. omega end alpha end Only single carbon-carbon bonds Linear, pack tightly; solids Red meat- highest % of SF; Chicken has lower % of Saturated fat 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

  6. omega end alpha end One double bond Canola oil and Olive oil high in monounsaturated FA 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

  7. omega end alpha end > 2 double bonds Corn, soybean, sunflower, safflower oils rich in polyunsaturated FA. 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

  8. Chain Length of Fatty Acids: Affects fluidity • Long chain Saturated FA • > 12 Carbons • Solid at room temperature • Medium chain FA (e.g coconut oil) • 6 - 10 Carbons • Short chain FA: (e.g. dairy fats) • < 6 Carbons • Direct absorption from intestinal cell into the blood

  9. Essential fatty acids: EFAs • Humans cannot synthesize double bonds within the fist 9 carbons from the methyl end (n) of any fatty acid chain • Fatty acids with double bonds in those locations must therefore come from the diet—and are considered essential • Thus, EFA are (poly)unsaturated • There are no essential saturated fats

  10. Essential Fatty Acids • Omega-3 fatty acids: alpha linolenic acid (C18:3; w3) • Omega- 6 fatty acids: Linoleic acid (C18:2; w6) • Role in • Immune systems • Cardiovascular systems • Nervous systems • vision, • cell membrane, • production of eicosanoids • Omega 9 FA necessary but not essential • oleic acid (C18:1; w-9)

  11. omega end alpha end 1st double bond is located on the 3rd carbon from the omega end Essential Fatty Acid- Omega-3 (alpha-linolenic acid) 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

  12. Omega-3 Fatty AcidsFamily • Alpha linolenic acids • Eicosapentaenoic acid (EPA) (C20:5; w3) • Docosahexaenoic acid (DHA)(C22:6;w3) • Primarily from fish oil & also canola or soybean oil • Metabolized to form eicosanoids: • hormone-like compounds required for growth • Regulates blood pressure, childbirth, clotting, immune responses, & stomach secretions for growth • Recommend: ~2 servings fish/week • 1g/d needed esp in cases of CVD

  13. omega end alpha end 1st double bond is located on the 6th carbon from the omega end Essential Fatty Acid- Omega-6 (alpha-linoleic acid) 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

  14. Omega-6 Fatty AcidsFamily • Linoleic acid, • Arachidonic acid , • Dihomo-gama linoleic acid • Metabolized to form eicosanoids • In vegetable oils; need ~ 1 TBS a day • Read page 184

  15. Signs and Symptoms of Essential Fatty Acids Deficiency • Flaky, itchy skin • Diarrhea • Infections • Retarded growth and wound healing • Anemia

  16. esterification/reesterification deesterification Deesterification can form di and monoglycerides This is the breaking of FA from glycerol, reesterfication is the reverse Free FA, monoglyceride and glycerol can freely cross the cell membrane Triglycerides: ester bonds H H--C--OH H--C--OH H--C--OH H Fatty Acid Fatty Acid Fatty Acid H O H--C--O--C-- O H--C--O--C-- O H--C--O--C-- H Fatty Acid + Fatty Acid Fatty Acid

  17. Functions of Triglycerides • Provide energy: for light activity, rest & sleep • Efficient storage of energy: • 9kcal/kg; adipose cells can increase in size x50 to accommodate more fat pg 166 • More cells can be synthesised, body efficient in storing fats • Insulation • Loss of subcutaneous fats results in Lanugo • Downy hair that appears after a person has lost much fat through semi-starvation • Seen in people with anorexia nervosa • Protection • Transport fat-soluble vitamins • Satiety • Flavor and mouth feel

  18. Functions of Phospholipids • Non-essential • Cell membrane • Eicosanoid synthesis • Lecithin emulsifies fat to micelles (small fat droplets) • Plenty in peanuts, egg yolk, liver, soybean • Bile acids contains lecithins, acids,cholesterol

  19. Sterols • Waxy substance, no glycerol or FA backbone; a multi-ringed structure • Non essential; made from acetyl CoA • Cholesterol is a sterol only in animal products • Essential component of cell membrane • Forms important hormones • Estrogen, testosterone, vitamin D • Precursor of bile acids • See table 6.2

  20. Digestion of Fat in the Stomach • Little digestion in stomach aided by • Gastric lipase • Short & medium FA chain triglycerides • Long FA chain unaffected

  21. Digestion of Fat in the Small Intestine (SI) • SI is the primary site of fat digestion • Cholecystokinin (CCK): hormone in duodenum • causes the gallbladder to release bile and the • the pancreas to secrete pancreatic lipase • Pancreatic colipase- coenzyme • Products of fat digestion are • Monoglycerides, glycerol &fatty acids

  22. Absorption • FA, Glycerol and monoglycerides form little micelles /spherical structures • Absorption is by enterocyte thru the villi of SI • Short chain FA ---hepatic portal vein to liver • 95 % absorption rate

  23. Absorption • Long Chain FA: reformed into triglycerides • Packaged into lipoproteins • Large lipid droplet surrouned by protein, triglyceride, phospholipid and cholesterol • Chylomicrons: LPPs produced by small intestine

  24. Absorption • Lipoproteins • Lymphatic system via lacteals & then circulatory system • In blood vessels • Lipoprotein Lipase breaks triglycerides in chylomicrons • FA are absorbed by cells (muscle or adipose) • Takes 2-10 hrs to clear the chylomicrons from the blood circulatory system

  25. From Last week • Chylomicrons consist of: • A core made of lipids (triglycerides and cholesterol bound to fatty acids) • A shell made of cholesterol, protein, phospholipids and apolipoproteins (apolipoproteins aid in transport of chylomicrons to target cells) • Chylomicrons transport diet-derived lipids (mostly triglycerides) from the small intestine to other body locations. • The chylomicron gets smaller and smaller as it hands off the triglycerides to body cells. • After ~ 2-10 hours following absorption, only protein remnants and small amounts of lipid remain. • The liver picks up these remnants, removing them from the circulation.

  26. Liver synthesizes fat and cholesterol using FA, glycerol and triglycerides in vessels Processes them into Very Low Density Lipoprotein (VLDL) Transport cholesterol, & lipid produced by the liver VLDL goes into the blood stream from the liver Are broken down by Lipoprotein Lipase, release FA, glycerol FA taken up by body cells As the triglycerides are removed, the lipoproteinbecomes heavier, or more dense The lipoprotein is now converted into a low-density lipoprotein, or LDL, containing mainly cholesterol. Fate of fats and cholesterol made in the liver

  27. Uptake of LDL • Receptor Pathway for cholesterol • A process by which LDL is bound by cell receptors and incorporated into cells where cholesterol is broken down or used for building cells • when diet is low in saturated fat and cholesterol • Removes LDL from circulation

  28. Uptake of LDL • Scavenger pathway for cholesterol • A process by which LDL is taken by scavenger cells embedded in the endothelium of blood vessels • LDL is oxidized, forms a plaque, • a thick, hard deposit that can clog those arteries • Atherosclerosis • Antioxidants (Vit C, Vit E, carotenoids) found in fruits and vegetables reduces risk of coronary heart disease • Prevent oxidation of LDLs

  29. High Density Lipoprotein (HDL) • Synthesized by liver and intestine • High proportion of protein, thus dense • Picks up cholesterol from dying cells and other sources • Transfers cholesterol to other lipoprotein for transport to the liver for excretion • HDL can also transfer directly back to the liver

  30. Benefits of (a high) HDL (level) • Remove cholesterol from the blood stream • HDL may block oxidation of LDL • Reduce risk of heart disease • High HDL in blood = good • Low HDL in blood = problems • Little cholesterol to the liver for excretion • Common in men

  31. Hydrogenation of Fatty Acids • Process used to solidify an oil • Forms trans fatty acid with hydrogen on opposite sides of the double bond. • Causes backbone to remain straight and allows tighter packing just like saturated FA • CIS configuration common in mono & polyunsaturated fatty acid • See figure 6.15

  32. Health Dangers of Excessive Trans Fatty Acid • Raises LDL levels • Lowers HDL • Increases risk for heart disease • Current intake is~3% of total kcals (10g/d) • FDA requires trans fat content on food labels • Examples of spreads with low or no trans fats: • Smart beat • Promise • Fleischmann

  33. Minimize Intake of Trans Fatty Acid • Limit use of hydrogenated fats • Limit deep-fried foods • Limit high fat baked goods • Limit use of non-dairy creamers • Restaurant foods high in trans-fatty acids and saturated FA • Read page 222

  34. Rancidity • Decomposed oils emit an odor, taste, sour taste due to • Breakdown of the C=C double bonds by ultraviolet rays, and O2 • Yields unpleasant odor, flavor, and sickness when consumed • Limits shelf life • Food more prone • Food with high PUFA • Deep fried foods • Powdered eggs • Powdered milk, cake mixes, • Fat in fish

  35. Prevention of Rancidity • Hydrogenation • Addition of vitamin E • Addition of Butylated hydroxyanisol (BHA) and Butylated hydroxytolune (BHT) • Common synthetic antioxidants

  36. Emulsifiers • Monoglycerides • Diglycerides • Polysorbate 60 • Eggs added to cake batter • Added to salad dressing and cake mixes to vegetable oil in water

  37. American Heart Association’s Recommendations • AI set by American Heart Association • 20%-30% of total energy intake (TEI) from all fats • 47-70g/d • 7% -10% of TEI from saturated and trans fat • 200-300 mg cholesterol /day • Limit intake of trans fatty acid • Low fat is not recommended for children under 2 years of age • See also Tables 6.6 & 6.7 • Essential fatty acids intake~ 5 % of total energy intake • Linoleic acid (omega-6) 17g/d for men and 12 g/d for women • Alpha linolenic acid (Omega –3), 16 (men); 1.1 (women)

  38. Fats in Foods • Fat rich foods (~100% of energy as fat) • Salad oils • Butter • Margarine: 80% • Mayonnaise • Foods with 80% energy as fat • Walnuts • Bologna • Avocadoes • Bacon • Peanut – butter: 75 % • Cheddar cheese: 75 %

  39. Fats in Foods • Foods with 35% of energy as fat • Eggs • Pumpkin pie • Cup cakes • Lean cuts • Meat-top round

  40. Animal Fats • 40-60% of fat is saturated • Saturated fats contributes to high LDL • Lauric acid: 12 C • Myristic acid: 14 C • Palmitic: 16 • Dairy foods also high in fats that raise LDL levels in blood, rich in myristic acid

  41. Plant Oils • Mostly unsaturated FA: 73-94% of total • Canola, olive, & peanut oils: • 50-80% monounsaturated FA • Corn, cottonseed, sunflower, soybean, safflower: • mostly poly-unsaturated FA • 50-80% of total fat • Supply omega -3 and omega- 6 FA

  42. FAT-Free = “all you can eat” • Sales of reduced fat food were projected to rise to 32 billion by year 2001 • When fat is removed, sugar is added in its place • Fat free = Calorie free • Calorie content is still similar to full-fat version • Eat reduced fat foods in moderation

  43. Fat Substitutes Z-trim • Starch derivative • Made from hulls of soybean, peas & rice or bran (corn or wheat) • Absorbs large amounts of water to form a gelatin-like product • Used in a variety of foods • Creates mouth-feel • Contains less calorie than fat but does not remove all calories • Not used for frying

  44. Fat Substitutes Dairy-Lo Used in milk and other dairy products • Contains eggs, milk protein treated with microscopic protein globules • Mouth feel of fat, without the fat • 1-2 kcal/gm due to pn & water • High water content

  45. Fat Substitutes Olestra (Olean) • Engineered fat • Fatty acids linked to sucrose • Not digested by human or bacterial enzymes • Yields no calories • Can be used in frying or can replace all fat in salad dressing and cakes • Problem: bind fat soluble vitamins and carotenoids in a meal • Over-consumption may cause cramping and loose stool • May bind to carotenoids in the meal

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