Lipids
Composed of C, H and few O
Basic unit is fatty acid (glyceride)
Triglyceride is the major form of lipid = 3 fatty acids
Fats and oils
Monounsaturated Fatty Acids
Polyunsaturated Fatty Acids
Saturated Fatty Acids
Essential Fatty Acids
Energy yielding (9 kcal /gm)
Sources of Dietary Lipids
Properties of Lipids
•
•
•
•
Do not readily dissolve in water
Fats are solid at room temperature
Oils are liquid at room temperature
Triglycerides are the main form of lipids in food
and body (storage)
• Energy dense (9 kcal /gm)
The building block of lipids are fatty acids
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
Note that all carbons have two hydrogens – this is a fully saturated
fatty acid.
Triglycerides
H
O
H--C--OH
HO-C-R
H
H--C--O--C-- R + H2O
O
H--C--OH
+
HO-C-R
O
H--C--O--C-- R + H20
O
H--C--OH
HO-C-R
H
Glycerol
O
O
H--C--O--C-- R + H20
H
+ 3 FA’s
(Ester bond)
Triglyceride +
3 H20
Triglycerides
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
desterfication
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
When two Hs are lost from two adjacent Carbons, a double
bond is formed. This is an unsaturated fatty acid.
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
Two or more double bonds results in a polyunsaturated fatty
acid.
The more double bonds, the lower the melting
point of a fat/oil
• Beef fat or lard has a large amount of saturated fatty acids
that are long. It is solid at room temperature.
• Butter has about the same number of saturated as
unsaturated fatty acids. Butter is beginning to melt at room
temperature.
• Vegetable oil is 100% unsaturated fatty acids. It is liquid at
room temperature and will solidify at around –5 °F.
• What about vegetable shortening?????
The chain length has an effect on how liquid a
fat/oil is at room temperature
• Long chain FA
> 12 Carbons
• Medium chain FA
6 - 10 Carbons
• Short chain FA
< 6 Carbons
Hydrogenation of Fatty Acids
• Process used to solidify an oil
• Addition of H to C=C double bonds
• Formation of trans fatty acid
Health Dangers of Excessive Trans Fatty Acid
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•
•
•
•
Raises LDL
Lowers HDL
Increases risk for heart disease
Current intake is~3% of total kcals
Soon to be on food labels
Minimize Intake of Trans Fatty Acid
• Limit use of hydrogenated fats
– partially hydrogenated vegetable oil
• Limit deep-fried foods
• Limit high fat baked goods
• Limit use of non-dairy creamers
Essential Fatty Acids
Body can only make double bonds after the 9th carbon
from the omega end
Needed for immune function, vision, cell membrane,
and production of hormone-like compounds
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
Primarily from fish oil
Also found in canola or soybean oil
Eicosapentaenoic acid (EPA) and docosahexaenoic acid
(DHA) are related
Metabolized to form eicosanoids
Recommend intake of ~2 servings of fish per week
Omega 3 (Alpha-linolenic acid, C18:3)
2C
2H
Eicosapentaenoic acid (EPA, C20:5)
2C
2H
Docosahexaenoic acid (DHA, C22:6)
Eicosanoids
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 Acid
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•
•
•
Found in vegetable oils and meat
Only need ~ 1 tablespoon a day
Arachidonic acid can be made from omega-6 (18:2 w6)
Metabolized to form certain eicosanoids
O
C
C
OH
H3C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
C
Omega 6 (linoleic acid, C18:2)
2C
2H
Dihomo-gamma-linolenic acid (C20:3)
2H
Arachidonic acid (C20:4)
Eicosanoids
Eicosanoids
Eicosanoids are a group of hormone-like compounds
Regulators of blood pressure, childbirth, clotting, immune
responses, inflammatory responses, & stomach secretions
By-pass the blood stream and work in the area of origin
Eicosanoids Have Different Effects
Omega-6 eicosanoids; Archidonic acid
increase blood cot
increase inflammatory responses
Omega-3 eicosanoids, DHA, EPA
decrease blood clotting
reduces heart attack
excess may cause hemorrhagic stroke???
Eicosanoids have different effects on different tissues
Signs and Symptoms of Essential Fatty Acids
Deficiency
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•
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Flaky, itchy skin
Diarrhea
Infections
Retarded growth and wound healing
Anemia
Phospholipids
Built on a glycerol backbone
Has at least one fatty acid replaced with phosphorus
compound
Found in body
Synthesized by the body as needed
Functions of Phospholipids
Makes up cell membrane
Eicosanoid synthesis
Emulsifier
Bile acids
Lecithins
Emulsifier
Hydrophilic end (attracts
water)
Hydrophobic end (attracts
lipid)
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Emulsification (Fig. 6-5)
Cell Membrane
Double layers of lipid, CHO, and protein
Controls passage of substances
Distinct identification structures
Sterols
A multi-ringed structure
Do not have a glycerol backbone
Waxy substance
Do not readily dissolve in water
Cholesterol is a sterol
Functions of Cholesterol
Essential component of cell membrane
Produced by the liver
Found only in animal products
Forms important hormones
Estrogen, testosterone, vitamin D
Precursor to bile acids
Digestion of Lipids
Where do dietary lipids go?
How does our body make lipid?
Where do lipids that our bodies make go?
Digestion of Fat in the Stomach
Gastric lipase works only in an acidic environment
Gastric lipase acts on triglycerides containing short & medium
chain fatty acid
Longer fatty acid chain is not affected by the stomach
Digestion of Fat in the Small Intestine
Primary site of fat digestion
CCK stimulates pancreas to release pancreatic lipase
Pancreatic colipase is release to help facilitate lipase enzyme
action
CCK stimulates the release of bile to help emulsify fat
Fat is broken down to monoglycerides and fatty acids
Transportation of Fat in the Bloodstream
Water (blood) and oil (fat) are incompatible
Unique system of fat transportation is needed
Fat
Transportation of Dietary Fat
What we do with it directly after eating it…
Re-formed into triglycerides
Packaged into chylomicrons
Lipoprotein lipase breakdown triglycerides in the
chylomicrons
Fatty acids are absorbed by cells
Takes 2-10 hours to clear chylomicron
Dietary Fat Absorption
Nutrient Absorption
Lipoproteins
Transportation of Synthesized Fat
Fat and cholesterol made primarily by the liver
Very Low Density Lipoprotein (VLDL)
VLDL remnant (or IDL)
Low Density Lipoprotein (LDL)
Receptor pathway for cholesterol uptake
Scavenger pathway for cholesterol uptake
Receptor Pathway
Scavenger Pathway
Scavenger WBC removes (oxidized) LDL from
circulation
Prevents oxidized LDL from returning to circulation
Build-up of plaque on walls of the blood vessels
Leads to atherosclerosis
Causes: smoking, diabetes, HTN, homocysteine,
LDL
Antioxidant
Reduces oxidation
Slows LDL uptake into scavenger cells
Need for supplements of antioxidants?
Composition of Lipoproteins
High Density Lipoprotein (HDL)
Synthesized by liver and intestine
High proportion of protein
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
Pre-menopausal women have higher HDL
Functions of Lipids
Provide energy
Efficient storage of energy
Insulation
Protection
Transport fat-soluble vitamins
Satiety
Flavor and mouth feel
Rancidity
Decomposed oils
Breakdown of the C=C double bonds by ultraviolet
rays, O2
Yields unpleasant odor and flavor
PUFA more susceptible
Limits shelf life
Prevention of Rancidity
Hydrogenation
Addition of vitamin E
Addition of Butylated hydroxyanisol (BHA) and
Butylated hydroxytolune (BHT)
American Heart Association’s
Recommendations
No RDA for fat
< 30% of total energy intake (TEI) from all fats
8% -10% of TEI from saturated fat
< 10% of TEI from PUFA
< 15% of TEI from MUFA
< 300 mg cholesterol /day
Limit intake of trans fatty acid
Low fat is not recommended for children under 2 years of age
The National Cholesterol Education Program
Reduce fat intake to 7% of total energy intake
from saturated fat if elevated LDL does not
respond to previous reduction
Limit cholesterol to ~300 mg/day
Reduce cholesterol to 200 mg/day if LDL
remains high
Here fat, there fat, everywhere fat, fat
Read labels carefully
Use of monoglycerides and diglycerides in foods
High in nuts, cheeses, fatty meats, whole milk
Reduce Fat Labels
“Low fat”
< 3 gm of fat/serving
“Reduced fat” or “Less fat”
> 25% less fat than reference food
“Fat free”
< 0.5 gm of fat/serving
“Fat Free” = “All You Can Eat”?
Sales of reduced-fat foods are projected to soar to ~$32 billion
by year 2001
When fat is removed, sugar is usually added in its place
“Fat Free” is NOT “Calorie Free”
Calorie content is still similar to full-fat version
Eat “Reduced-fat” foods in moderation
Fat Substitutes
Z-trim
Starch derivative
Binds with water to create mouth-feel
Contains less calorie than fat
Fat Substitutes
Simplesse
Egg and milk protein globules
High water content
1-2 kcal/gm
Not heat stable
Fat Substitutes
Olestra (Olean)
Engineered fat
Fatty acids linked to sucrose
Not digested by enzymes or bacteria
Yields no calories
Addition of fat soluble vitamins
Over-consumption may cause cramping and loose stool
May bind to carotenoids in the meal
Uses for Fat Substitutes
Use in moderation
Use in place of high fat option
Avoid over-eating
Treat it as you would a full fat food
Signs of a Heart Attack
Intense, prolong chest pain
Shortness of breath
Sweating
Nausea and vomiting
Dizziness
Weakness
Jaw, neck, shoulder pain
Irregular heartbeat
Coronary Heart Disease
Symptoms take years to develop
Plaque build-up can begin in childhood
Myocardial infarction (heart attack)
Stroke
Conditions Leading to a Heart Attack
Risk Factors for Heart Disease
Family history
Smoking
High blood pressure
High blood cholesterol (hyperlipidemia)
>200 mg/dl of total cholesterol
HDL < 35 mg/dl
Diabetes
Lack of regular exercise and obesity
Reducing Your Risks--Primary Prevention
Reduce dietary saturated fat and cholesterol
Increase MUFA and PUFA to recommended amounts
Increase dietary fiber
Increase activity; develop a exercise routine
Adequate caloric intake to maintain healthy weight
Secondary Prevention (After a Heart Attack)
Primary prevent techniques
Medication
Hormone therapy
Megadoses of vitamin E (400-800 IU/day)
Myth: Women Don’t Die of Heart Disease
44% of women die from cardiovascular disease
(versus 38% in men)
33% of women die from heart disease(versus 31% in
men)
Doctors are more likely to consider heart disease for
men (than women)
Men develop heart disease earlier in life
Early research focused on men
Benefits of Female Hormones?
Not fully understood
Decrease LDL
Increase HDL
Estrogen is associated with decrease risk
Women’s risk for heart disease increases after menopause
Estrogen therapy
Medical Therapy
Cholestin (Mevacor)
Derived from Chinese red yeast
Successful in reducing blood cholesterol
Pure cholestin is very expensive
Benecol and Take Control
Plant sterol ester
Cholesterol-lowering effect
Compete with cholesterol in the micelle and reduce
absorption of dietary cholesterol
Other Strategies
Healthy body weight
Moderate to vigorous physical activity daily
nonsmoker
Alcohol in moderation
Intakes of cereal fiber, omega-3 fatty acids, and
folate
Low intakes of sat. fat and higher intakes of PUFAs
Low glycemic index load
CVD Detection
C-reactive protein (hs-CRP)
Measures protein made in the liver in response to
inflammation
Inexpensive
Fast CT-scan
X-ray revealing calcium deposits (plague composition)
Expensive