Chapter 5
The Lipids:
Triglycerides,
Phospholipids,
and Sterols
Chemist’s View of Fatty Acids and
Triglycerides
• Preview of lipids
– Triglycerides: glycerol and three fatty acids
– Fatty acids
 Saturated or unsaturated
– Omega-3 and omega-6 fatty acids
 18-carbon polyunsaturated fatty acids
Fatty Acids
Saturated fatty acids
- Are fully loaded with hydrogens
- Fully saturated with hydrogens
- No double bonds
Fatty Acids
Unsaturated fatty acids
- Has at least one double bond
- Not every carbon is “saturated” with hydrogens and
therefore must form a double bond.
Polyunsaturated fatty acid
- Has more than one double bond.
18-Carbon Fatty Acids
Name
Number of
Carbon
Atoms
Number of
Double
Bonds
Saturation
Common Food Sources
Stearic acid
18
0
Saturated
Most animal fats
Oleic acid
18
1
Monounsaturated
Olive and canola oils
Linoleic acid
18
2
Polyunsaturated
Sunflower, safflower, corn,
and soybean oils
Linolenic acid
18
3
Polyunsaturated
Soybean and canola oils,
flaxseed, walnuts
NOTE: Chemists use a shorthand notation to describe fatty acids. The first
number indicates the number of carbon atoms; the second, the number of the
double bonds. For example, the notation for stearic acid is 18:0.
Characteristics of Solid Fats and
Oils
Which fatty acids tend to
be solid at room
temperature?
a) Unsaturated
b) Saturated
Answer:
b
Explanation:
Saturated fats tend to be solid
because their tails are straight and
they “stack” well, for example,
butter. Fats with a double bond
have “kinked” chains, they don’t
“stack,” therefore form liquids, for
example, oil.
Fats spoil (go rancid) when
exposed to oxygen.
Polyunsaturated fats spoil most
readily. Heat and light exposure
speed up rancidity.
Diagram of Saturated and
Unsaturated Fatty Acids Compared
Fatty Acid Composition of Common
Food Fats
Hydrogenation
• Hydrogenation
– Protects against oxidation – prolonging shelf
life
– Alters the texture of food
• Trans-Fatty Acids
– Act like a saturated fat in the body
– Heart disease connection being researched
Degree of Unsaturation
• Saturated fat is more resistant to oxidation
– Oxidation = substance combines with oxygen and
losses an electron
• Monounsaturated fat is slightly less susceptible
to spoilage
• Polyunsaturated fat spoils most readily
• Protection from rancidity
– Seal in airtight containers away from light
– Add antioxidants
– Hydrogenation
Phospholipids
• Solubility in fat and water
• Emulsifiers in food industry
• Lecithin is best-known
– Found in eggs, liver,
soybeans, wheat germ, and
peanuts
• Food sources
– Seafood, eggs, seed oils
and meat.
• Roles
– Part of cell membranes
– Emulsifiers
Sterols
• Food sources
– Cholesterol
– Plant sterols
• Roles of sterols
– Made in the body
– Structural component of
cell membranes
– Liver produces 8001500mg cholesterol per
day
Lipid Digestion
• Fats are hydrophobic
– Digestive enzymes are hydrophilic
• Goal of fat digestion
– Dismantle triglycerides
 Monoglycerides, fatty acids, and glycerol
Fat Digestion in the GI Tract
The Beginning of Fat Digestion
• Mouth
– Lingual lipase plays role in fat digestion in infants
• Stomach
– Strong muscle contractions
– Gastric lipase
– Little fat digestion
Lipid Digestion in the Small Intestine
• Cholecystokinin (CCK)
– Gallbladder releases bile
– Bile acts as emulsifier
• Pancreatic lipase
• Hydrolysis
– Triglycerides and phospholipids
• Bile routes
– Effect on blood cholesterol levels
Emulsification of Fat by Bile
• How An Emulsifier Works
– Lipids are hydrophobic
– Separate from watery fluids of digestion
– Digestive enzymes are hydrophilic
– Bile from the liver emulsifies lipids
– Enzymes are then able to break down lipids to
monoglycerides and fatty acids
Enterohepatic Circulation
2
Answer:
1. Liver
2. Bile
3. Small
4. Colon
1
3
4
Lipoproteins
• Lipoproteins
– LDL (Low Density Lipoproteins) “Bad”
• Composed primarily of cholesterol
• Transport lipids to the tissues
• High LDL is associated w/ higher risk of heart
attack
– HDL (High Density Lipoproteins) “Good”
• Composed primarily of protein
• Transport cholesterol from the cells to the liver
• Seems to have a protective effect
Lipoproteins
• Health Implications
– High LDL – associated with higher risk of
heart attack
– High HDL – has a protective effect
– Factors that lower LDL and raise HDL
–
–
–
–
–
–
Weight Control
Replace Sat Fat with Mono- & PolyUnsaturated fat
Soluble Fibers
Phytochemicals
Moderate alcohol consumption
Physical activity
Sizes and Compositions of the
Lipoproteins
Roles of Triglycerides
• Provide the cells with energy
– Virtually unlimited ability to store
fat energy
• Adipose tissue stores body fat
– Secretes hormones (adipokines)
• Other uses of fat in the body
–
–
–
–
Skin insulation
Shock absorption
Cell membrane material
Cell signaling pathways
An Adipose Cell
Omega-6 and Omega-3 Fatty Acids
• Linoleic acid—Omega-6 fatty acid
– Essential fatty acid
 Can make other omega-6 fatty acids
– Sources: vegetable oils and meats
• Linolenic acid—Omega-3 fatty acid
– Essential fatty acid
 Must be supplied by food
– DHA
– EPA
Eicosanoids
• Eicosanoids
– “Hormonelike”
– Health benefits
• Omega-6 to Omega-3 ratio
• Fatty acid deficiencies
– Rare in the United States
– Symptoms
A Preview of Lipid Metabolism
1. _______ cells store fat
after meals.
2. Lipoprotein lipase
________ triglycerides.
3. Fat supplies ___ percent of
energy needs during rest.
4. During times of energy
deprivation, fat and lean
________ tissue are used
for energy.
Answer:
1. Adipose
2. Hydrolyzes
3. 60
4. Protein
Health Effects of Saturated Fats,
Trans Fats, and Cholesterol
•
•
•
•
Focus on quality and quantity
Current US diet contains excessive solid fats
Blood lipid profile
Heart disease
– Elevated LDL cholesterol a risk factor
 Saturated fats increase LDL cholesterol
o Promote blood clotting
 Ways to lower dietary saturated fat
 Trans fats increase LDL and lower HDL cholesterol
 Dietary cholesterol
Fat Links to Cancer and Obesity
• Cancer
– Promotion rather than
initiation of cancer
– Dietary fat and cancer risk
 Differs for various types of
cancer
• Obesity
– Cutting fat from diet often
reduce kcalories
– Dietary recommendations
Recommended Intakes of Saturated
Fat, Trans Fat, and Cholesterol
• DRI and Dietary Guidelines
– 20 to 35 percent of daily energy from fat
 Less than 10 percent from saturated fat
 As little trans fat as possible
– No longer limit to <300 mg cholesterol
– Average US consumption of fat
• Avoid getting too little fat
– Recommendation: one teaspoon of fat at meals
Health Effects of Monounsaturated
and Polyunsaturated Fats
1. Replacing ________ fats with
__________ fats helps reduce risk of
heart disease.
2. Regular consumption of omega-__ fatty
acids suppresses ___________, which
may protect against some cancers.
Answer:
1. Saturated,
unsaturated
2. 3; inflammation
Explanation:
Fish oil supplements
are available but not
recommended for
routine
supplementation due
to side effects.
Replacing Saturated Fat with
Unsaturated Fat
Portion sizes have been adjusted so that each of these foods
provides approximately 100 kcalories. Notice that for a similar
number of kcalories and grams of fat, the second choices offer
less saturated fat and more unsaturated fat.
…with these foods.
Replace these foods…
Saturated
Fat (g)
Unsaturated
Fat (g)
Total
Fat (g)
Olive oil (1 tbs)
2
9
11
Sunflower seeds (2
tbs)
1
7
8
Mixed nuts (2 tbs)
1
8
9
Avocado (6 slices)
2
8
10
5
Salmon (2 oz)
1
3
4
40
Totals
7
35
42
Saturated
Fat (g)
Unsaturat
ed Fat (g)
Total
Fat
(g)
Butter (1 tbs)
7
4
11
Bacon (2 slices)
3
6
9
Potato chips (10
chips)
2
5
7
Cheese (1 slice)
4
4
8
Steak (1'/2 0z)
2
3
Totals
18
22
Recommended Intakes of Monoand Polyunsaturated Fats
• 20 to 35 percent of kcalories from fat
– Includes essential fatty acids
 Established AI
• DRI
– Linoleic acid: 5–10 percent of daily energy
– Linolenic acid: 0.6–1.2 percent of daily energy
 No DRI for EPA and DHA
Selecting Groceries
• Fat-soluble vitamins
– A, D, E, and K
• Flavor, texture, and palatability
• Protein foods
– Best choices
• Milk and milk products
– Best choices
Cutting Fat Cuts kCalories and
Saturated Fat
Grocery Choices
• Vegetables, fruits, and grains
– Lowers consumption of fats
 Fats from avocado and olive benefits
 Provides vitamins, fiber, phytochemicals
– Caution on refined grain products
• Solid fats and oils
– Source of fat—discretionary or not
Food Labeling
•
•
•
•
Read food labels
Total fat, saturated fat, trans fat, cholesterol
Compare products
Percent Daily Value VS percent kcalories from fat
(How-To 5-3)
• Fat replacers
– Types
– Risks
 Nutrient absorption
Highlight 5
High-Fat
Foods—Friend
or Foe?
Guidelines for Fat Intake
• Lower saturated and trans fat
– Moderate kcalories
– Enough fats for good health
– Not too much of the harmful
fats
– Consumer education on
types of fat
• DRI recommendations
– Compatible with low rates of
disease
High-Fat Foods and Heart Health
• Olive oil
– Benefits for heart health
– Replace saturated fats
• Nuts
– Fat composition
– Benefits for heart health
 Blood pressure, LDL,
inflammation
– Cautious advice for dietary
inclusion
Fish
• Omega-3 fatty acids
– Benefits for heart health
 Benefits for hypertension or
atherosclerosis
– Dietary recommendations
• Environmental contaminants
– Mercury
High-Fat Foods and Heart Disease
• Saturated fat main determinant of LDL cholesterol
– Sources of saturated fat in the United States
 Meats
 Whole milk products
 Tropical oils
– Zero saturated fat is not possible
• Trans fat
– Limit hydrogenated foods
Two Meals Compared
The Mediterranean Diet
• Features of a traditional Mediterranean diet
– Low in saturated fat
– Very low in trans fat
– Diet composition




Whole foods—vegetables, legumes, fruits
Limited meat
Monounsaturated and polyunsaturated fats
Complex carbohydrates, fiber, and phytochemicals
• Benefits for heart disease risk
Mediterranean Diet Pyramid