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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
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 end
One 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 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 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 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
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-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 lipoproteinsLarge lipid droplet surrouned by protein,
triglyceride, phospholipid and cholesterol
Chylomicrons: LPPs produced by small intestine
AbsorptionLipoproteins 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 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
Hydrogenation
Addition of vitamin E
Addition 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 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-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-Lo
Used in milk and other dairy productsContains 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 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
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