Chap. 6: Lipids

Properties of Lipids

Non-polar: water insolubleEnergy density = Monomers: fatty acids & glycerol

LIPIDS: ClassesTrue fats: 95 % are triglycerides Fats: generic name, solid at room temp Oils:

Phospholipids

Sterols

Fatty Acid Structure:

omega end (methyl) alpha end

(Carboxylic)Hydrocarbon chain

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

Saturated Fatty Acid Structure

omega end alpha endOnly single carbon-carbon bondsLinear, pack tightly; solids Red meat- highest % of SF; Chicken has lower % of

Saturated fat

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

Monounsaturated Fatty Acid Structure

omega end alpha endOne double bond Canola oil and Olive oil high in monounsaturated FA

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

Polyunsaturated Fatty Acid Structure

omega end alpha end > 2 double bondsCorn, soybean, sunflower, safflower oils rich in

polyunsaturated FA.

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

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 chainFatty 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 AcidsOmega-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)

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

the omega end

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-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 growthRegulates blood pressure, childbirth, clotting, immune

responses, & stomach secretions for growth

Recommend: ~2 servings fish/week1g/d needed esp in cases of CVD

Essential Fatty Acid- Omega-6 (alpha-linoleic acid)

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

the omega end

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-6 Fatty AcidsFamily

Linoleic acid, Arachidonic acid , Dihomo-gama linoleic acidMetabolized to form eicosanoidsIn vegetable oils; need ~ 1 TBS a dayRead page 184

Signs and Symptoms of Essential Fatty Acids Deficiency

Flaky, itchy skinDiarrheaInfectionsRetarded growth and wound healingAnemia

Triglycerides: ester bonds

esterification/reesterification deesterification

Deesterification can form di and monoglyceridesThis is the breaking of FA from glycerol, reesterfication is the reverseFree FA, monoglyceride and glycerol can freely cross the cell membrane

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

Functions of Triglycerides

Provide energy: for light activity, rest & sleepEfficient 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

ProtectionTransport fat-soluble vitaminsSatietyFlavor and mouth feel

Functions of Phospholipids

Non-essentialCell membraneEicosanoid synthesisLecithin 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 structureNon essential; made from acetyl CoACholesterol 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 lipaseShort & medium FA chain triglyceridesLong FA chain unaffected

Digestion of Fat in the Small Intestine (SI)

SI is the primary site of fat digestionCholecystokinin (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 structuresAbsorption is by enterocyte thru the villi of SIShort chain FA ---hepatic portal vein to liver95 % absorption rate

Absorption

Long Chain FA: reformed into triglyceridesPackaged into lipoproteinsLarge lipid droplet surrouned by protein,

triglyceride, phospholipid and cholesterolChylomicrons: LPPs produced by small intestine

AbsorptionLipoproteins Lymphatic system via lacteals & then circulatory

systemIn blood vessels Lipoprotein Lipase breaks triglycerides in

chylomicronsFA 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 vesselsProcesses 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 intestineHigh proportion of protein, thus densePicks up cholesterol from dying cells and other sourcesTransfers cholesterol to other lipoprotein for transport to the liver for excretionHDL can also transfer directly back to the liver

Benefits of (a high) HDL (level)

Remove cholesterol from the blood streamHDL may block oxidation of LDLReduce risk of heart diseaseHigh HDL in blood = goodLow 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 levelsLowers HDLIncreases risk for heart diseaseCurrent intake is~3% of total kcals (10g/d)FDA requires trans fat content on food labelsExamples of spreads with low or no trans fats: Smart beat Promise Fleischmann

Minimize Intake of Trans Fatty Acid

Limit use of hydrogenated fatsLimit deep-fried foodsLimit high fat baked goodsLimit use of non-dairy creamersRestaurant 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 consumedLimits shelf lifeFood more prone Food with high PUFA Deep fried foods Powdered eggs Powdered milk, cake mixes, Fat in fish

Prevention of Rancidity

HydrogenationAddition of vitamin EAddition of Butylated hydroxyanisol (BHA) and Butylated hydroxytolune (BHT)Common synthetic antioxidants

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 Association20%-30% of total energy intake (TEI) from all fats 47-70g/d

7% -10% of TEI from saturated and trans fat200-300 mg cholesterol /dayLimit intake of trans fatty acidLow fat is not recommended for children under 2 years of ageSee also Tables 6.6 & 6.7Essential 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 saturatedSaturated 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 totalCanola, olive, & peanut oils: 50-80% monounsaturated FACorn, 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 2001When fat is removed, sugar is added in its placeFat free = Calorie freeCalorie content is still similar to full-fat versionEat reduced fat foods in moderation

Fat Substitutes

Z-trimStarch derivativeMade from hulls of soybean, peas & rice or bran (corn or wheat)Absorbs large amounts of water to form a gelatin-like productUsed in a variety of foodsCreates mouth-feelContains less calorie than fat but does not remove all caloriesNot used for frying

Fat Substitutes

Dairy-LoUsed in milk and other dairy products

Contains eggs, milk protein treated with microscopic protein globulesMouth feel of fat, without the fat1-2 kcal/gm due to pn & waterHigh water content

Fat Substitutes

Olestra (Olean)Engineered fatFatty acids linked to sucroseNot digested by human or bacterial enzymes Yields no caloriesCan be used in frying or can replace all fat in salad dressing and cakesProblem: bind fat soluble vitamins and carotenoids in a mealOver-consumption may cause cramping and loose stoolMay bind to carotenoids in the meal