Properties of Lipids
Do not readily dissolve in water
Fats are solid at room temperature
Oils are liquid at room temperature
Energy dense (9 kcal /gm)

Three Groups of Lipids
Triglycerides: the main form of lipids in food and body (storage)
Phospholipids
Sterols

Triglyceride (TG)
Structure
Contain Carbons (C), Hydrogens (H),
Oxygens (O)
Glycerol + 3 fatty acids

H
H--C--OH
H--C--OH
H--C--OH
H
Triglycerides
+
O
HO-C-R
O
HO-C-R
O
HO-C-R
H O
H--C--O--C-R + H2O
O
H--C--O--C-R + H20
O
H--C--O--C-R + H20
H
(Ester bond)
Glycerol + 3 FA’s Triglyceride +
3 H
2
0

H
H--C--OH
H--C--OH
H--C--OH
H
Triglycerides
+
Fatty Acid
Fatty Acid
Fatty Acid
H O
H--C--O--C-Fatty Acid
O
H--C--O--C-Fatty Acid
O
H--C--O--C-Fatty Acid
H esterification desterfication

Phospholipid
Built on a glycerol backbone
Has at least one fatty acid replaced with phosphorus compound
Found in body
Synthesized by the body as needed

Phospholipid Structure

Functions of
Phospholipids
Make up cell membrane
Emulsifier
 Bile acids
 Lecithins
 Improves food products

Emulsifier
Hydrophilic end
(attracts water)
Hydrophobic end
(attracts lipid)

Emulsification

Cholesterol
Most common sterol
A multi-ringed structure
Does not have a glycerol backbone
Waxy substance
Do not readily dissolve in water
Cholesterol is a sterol

Cholesterol Structure

Dietary Sources of
Cholesterol
Found in animal products only
Never found in plants
However ↑ saturated fat intake ↑ serum cholesterol

Serum (blood)
Cholesterol
Dietary cholesterol
Endogenous cholesterol
 Made in liver
 Increases with increased SFA intake

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

Fatty Acids
Simplest form of lipids
Common to most lipids, in the body and in foods
Chain of 4-26 carbons bonded together, flanked by hydrogens
Alpha end: is an acid
Omega end: a methyl group
Fats in foods are generally fatty acid mixtures

Differences in
Fatty Acids
Number of carbons
Degree of saturation
 Number of single or double bonds in carbon chain
 Saturated
 Monounsaturated
 Polyunsaturated
Point of first unsaturated bond
 Omega-3
 Omega-6

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 stearic acid (C18:0) alpha end

Saturated Fatty Acids
(SFA)
All the bonds between carbons are single connections and the carbons are filled with hydrogen
Foods containing primarily saturated fats tend to be solid at room temperature
Medium chain (coconut oil) and shortchain saturated fatty acids (dairy fat) may be liquid

Saturated Fatty Acids
Don’t spoil easily, therefore longer shelf life
High intakes of sfa are associated with an increased risk of cardiovascular disease

Sources of SFA
Animal fats (meat, dairy)
Tropical oils (coconut and palm oil)
Hydrogenated fats

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 degree of saturation: single carbon bond stearic acid: C18:0

Monunsaturated
Fatty Acids (MFA)
One double bond between the carbons (missing hydrogens)
Liquid at room temperature
Easily oxidized → becomes rancid
 Double bonds are weak points
 Easily broken by oxygen (oxidized)

Monounsaturated
Fatty Acids
Canola, olive, peanut oil contain a high percentage of monounsaturated fatty acids
MFA decreases CVD risk

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
One double bond
ω-9 C18:1 alpha end

Polyunsaturated
Fatty Acids (PUFA)
More than one double bond between the carbons
Liquid at room temperature
Easily oxidized
Polyunsaturated fat decreases
CVD risk when substituted for SFA

Polyunsaturated
Fatty Acids
Corn, soybean, sunflower, and safflower oils are rich in polyunsaturated fatty acids (PUFA)

Polyunsaturated Fatty
Acid Structure
(Fig. 5-1-C)
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
> 2 double bonds alpha end

Fatty Acid Profiles in Foods

Hydrogenation of Fatty
Acids
Addition of H to C=C double bonds
Breaks double bonds
Formation of trans fatty acid
(similar to shape of saturated fatty acid)

Hydrogenation of
Fatty Acids
Process used to solidify an oil
Resistant to oxidation
 Increases shelf life
 Can be reused longer in frying
However resulting trans fatty acids are associated with ↑ CVD risk

Cis and Trans Fatty Acid

Health Dangers of
Trans Fatty Acids
Raises LDL
Lowers HDL
Increases risk for heart disease
Current intake is~3% of total kcals
Soon to be on food labels

Sources of
Trans Fatty Acid
Stick margarine
Shortening
Crackers
Hydrogenated fats
Deep-fried foods
High fat baked goods
Non-dairy creamers

Rancidity
Decomposed oils
Breakdown of the C=C double bonds by ultraviolet rays, &/or O
2
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)

Functions of Fats
Provide essential fatty acids
Provide energy (muscles and many organs burn fat)
Supply fat soluble vitamins
Satiety
Texture and flavor

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 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 Acid
Primarily from fish oil
Also found in canola or soybean oil
Recommend intake of ~2 servings of fish per week

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
Found in vegetable oils
Only need
~ 1 tablespoon a day

Essential Fatty Acids
Omega-3 Omega 6
Alpha-linolenic acid Linolenic acid
DHA EPA Arachidonic Acid
(docosahexanoic (eicosapentaenoic acid) acid)

Effects of Essential
Fatty Acids
Archidonic acid (Omega-6 )

 increase blood clotting increase inflammatory responses
DHA, EPA (Omega-3)
 decrease blood clotting

 reduces heart attack excess may cause hemorrhagic stroke
 large amounts may decrease inflammation pain with rheumatoid arthritis

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

Functions of Body Fat
Energy store
 Adipose cells
 1 pound fat = 3500 calories
Insulation
 Subcutaneous fat
Protection
 Internal organs

Lipids in Foods

Hidden Fat
Look on the Nutrition Facts
Look on the lists of ingredients
Control portion size

Reduced Fat Foods
Sugar is commonly added in place of fat
Check calorie content

Fat Substitutes
Water (diet margarine)
Z-trim (starch derivative that binds with water)
Fiber cellulose (Maltrin, Stellar, Oatrim)
Dairy-Lo (protein globules)
Olestra (links fatty acid to sucrose)
 not digested
 fat-soluble vitamins issue

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
Pancreas release lipase
Bile acid emulsifies digested fat
Fat is broken down to monoglycerides and fatty acids

Absorption of Fat
Diffuse into the absorptive cells
Short and medium chain (<12 C) fatty acids are water soluble
 Enters the portal system
Long chain fatty acids reforms into TG
 Enters the lymphatic system

Carrying Fat in the
Bloodstream
Water (blood) and oil (fat) are incompatible
Unique system of fat transportation is needed
Fat

Transportation of
Digested Fat
Re-formed into triglycerides
Packaged into chylomicrons
Lipoprotein lipase breaks down triglycerides in the chylomicrons
Fatty acids are absorbed by cells
Takes 2-10 hours to clear chylomicron

Lipoproteins

Transportation of
Synthesized Fat
Fat and cholesterol made primarily by the liver
Very Low Density Lipoprotein (VLDL)
Low Density Lipoprotein (LDL)
Receptor pathway for cholesterol uptake
Scavenger pathway for cholesterol uptake

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 plaque and atherosclerosis
Causes: smoking, diabetes, HTN, homocysteine, LDL

Antioxidant
Reduces oxidation
Slows LDL uptake into scavenger cells
Need for supplements of antioxidants?

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 lipoproteins 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

Recommendation
No RDA
4% of total kcal should come from essential fatty acids
No more than 15% from PUFA
Current diet supplies ~33% of total kcal from fat
 much from animal, whole milk, pastries, cheese, margarine, and mayo

Dietary Reference
Intakes (2002 Update)
20-35% total calories from fat
≤30% with typical American diet
Up to 35% with more monunsaturated fat

American Heart Association
Population Guidelines
≤10% total calories from lipid-raising fats (saturated fat and trans fat)
≤10% total calories from polyunsaturated fat
At least 10% of calories from monounsaturated fat
<300 mg cholesterol/day
Eat two servings of fish/week