Chap. 6: Lipids

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

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

Fatty Acid Structure: omega end (methyl) alpha end (Carboxylic) 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 (methyl) alpha end (Carboxylic) Hydrocarbon chain

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

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 alpha end One double bond Canola oil and Olive oil high in monounsaturated 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 omega end alpha end > 2 double bonds Corn, soybean, sunflower, safflower oils rich in polyunsaturated FA.

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

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

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)

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 omega end alpha end 1st double bond is located on the 3rd carbon from the omega end

Omega-3 Fatty Acids Family 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

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 omega end alpha end 1st double bond is located on the 6th carbon from the omega end

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

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

Triglycerides: ester bonds H H--C--OH Fatty Acid H O H--C--O--C-- O H Fatty Acid + Fatty Acid Fatty Acid 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

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

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

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

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

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

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

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

Absorption Lipoproteins In blood vessels 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

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.

Fate of fats and cholesterol made in the liver 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 lipoprotein becomes heavier, or more dense The lipoprotein is now converted into a low-density lipoprotein, or LDL, containing mainly cholesterol.

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

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

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

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

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

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

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

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

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

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

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)

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 %

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

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

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

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

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

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

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