Transcript C=C--C--C =C--C--C=C

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:
H H H H H H H H H H H H H H H HHO
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)
(Carboxylic)
Hydrocarbon chain
alpha end
Saturated Fatty Acid Structure
H H H H H H H H H H H H H H H HHO
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 HH 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
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Medium chain FA (e.g coconut oil)
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6 - 10 Carbons
Short chain FA: (e.g. dairy fats)
< 6 Carbons
 Direct absorption from intestinal cell into the blood
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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
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Essential Fatty Acids
Omega-3 fatty acids: alpha linolenic acid (C18:3; w3)
Omega- 6 fatty acids: Linoleic acid (C18:2; w6)
Role in
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Immune systems
Cardiovascular systems
Nervous systems
vision,
cell membrane,
production of eicosanoids
Omega 9 FA necessary but not essential
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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 HH 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
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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
H--C--OH
Fatty Acid
H--C--OH
+
Fatty Acid
H--C--O--C-- Fatty Acid
O
H--C--O--C-- Fatty Acid
Fatty Acid
H--C--OH
O
O
H--C--O--C-- Fatty Acid
H
H
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:
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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
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Loss of subcutaneous fats results in Lanugo
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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
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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
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Pancreatic colipase- coenzyme
Products of fat digestion are
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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
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Lymphatic system via lacteals & then circulatory
system
In blood vessels
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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:
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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.
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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
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Very Low Density Lipoprotein (VLDL)
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Transport cholesterol, & lipid produced by the liver
VLDL goes into the blood stream from the liver
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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
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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,
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a thick, hard deposit that can clog those arteries
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Atherosclerosis
Antioxidants (Vit C, Vit E, carotenoids) found in
fruits and vegetables reduces risk of coronary heart
disease
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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
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Hydrogenation of Fatty Acids
Process used to solidify an oil
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Forms trans fatty acid with
hydrogen on opposite sides of the
double bond.
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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:
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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
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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
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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
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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
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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
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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)
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Salad oils
Butter
Margarine: 80%
Mayonnaise
Foods with 80% energy as fat
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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
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Animal Fats
40-60% of fat is saturated
Saturated fats contributes to high LDL
Lauric acid: 12 C
 Myristic acid: 14 C
 Palmitic: 16
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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