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Chapter 5
The Lipids: Fats
and Oils
Ask Yourself
True or False?
1. The body can store fat in virtually unlimited
amounts.
2. Dietary cholesterol is found only in animal foods.
3. A person’s blood level of cholesterol is a
predictor of that person’s risk of having a heart
attack.
4. For the health of your heart, the fat you should
avoid eating, most of all, is cholesterol.
5. The more monounsaturated fats you consume,
the better it is for your health.
Ask Yourself
6. Fruits are essentially fat-free.
7. In general, the softest margarines are
the most polyunsaturated.
8. Polyunsaturated fat has the same
number of calories as saturated fat.
9. All the foods you eat should contain
less than 10% of calories from
saturated fat.
10. No one is free of atherosclerosis.
A Primer on Fats
• Lipids: a family of compounds that
includes:
 Triglycerides (fats and oils)
 Phospholipids (lecithin)
 Sterols (cholesterol)
• Obvious sources of fat are oil, butter,
margarine, and shortening.
• Other foods contributing fat include
meat, nuts, mayonnaise, salad
dressings, eggs, bacon, gravy, cheese,
ice cream, and whole milk.
A Primer on Fats
• Fats
Lipids that are
solid at room
temperature.
• Oils
Lipids that are
liquid at normal
room temperature.
Muscles derive
fuel from fat.
A Primer on Fats
Within the fat cell, lipid is
stored in a droplet. This
droplet can enlarge, and
the cell membrane will
grow to accommodate its
swollen contents.
• After eating, the body
stores some fat as an
energy reserve.
• The body has unlimited
potential to store fat.
• Excess carbohydrate and
protein can be converted to
fat, but they cannot be
made from fat.
• One pound of body fat is
worth 3,500 calories.
Fat droplet
Cell membrane
Cell nucleus
A Primer on Fats
• Satiety
The feeling of
fullness or
satisfaction that
people feel after
meals.
 Fats slow the rate
at which the
stomach empties.
A Closer View of Fats
• Excess energy from the energyyielding nutrients is stored as fat.
• The fat is first broken into
fragments called fatty acids.
• Fatty acids
Basic units of fat composed of chains of
carbon atoms with an acid group at one
and and hydrogen atoms attached all
along their length.
A Closer View of Fats
About 95 percent of the
lipids in foods and in the
human body are
triglycerides.
• Triglycerides
The major class of
dietary lipids, including
fats and oils.
• A triglyceride is made
up of three units known
as fatty acids and one
unit called glycerol.
• Glycerol
An organic compound
that serves as the
backbone for
triglycerides.
G
l
y
c
e
r
o
l
Fatty acid
+
Fatty acid
Fatty acid
Glycerol + Fatty acids
Triglyceride
A Closer View of Fats: Other Lipids
•Phospholipid
A lipid similar to a triglyceride but containing
phosphorus; one of the three main classes of lipids.
Examples include:
 Lecithin
A major constituent of cell membranes,
manufactured by the liver and found in many
foods.
•Sterols
Lipids with a structure similar to that of cholesterol;
one of the three main classes of lipids.
Examples include:
 Cholesterol
One of the sterols, manufactured in the body for
a variety of purposes.
A Closer View of Fats
• Fatty Acids differ in chain length or
the number of carbons in a fatty
acid.
• Chain length affects solubility.
• Fatty acids can be:
Short-chain
Medium-chain
Long-chain
A Closer View of Fats
• Fatty acids differ in the degree of
saturation.
• Saturation refers to the chemical
structure—specifically to the number of
hydrogens the fatty acid chain holds.
Saturated fatty acids are filled to
capacity with hydrogen.
Unsaturated fatty acids hold an
“empty spot” or point of unsaturation.
Saturated vs. Unsaturated Fats
• Saturated fatty acid
A fatty acid carrying the maximum possible
number of hydrogen atoms (having no points of
unsaturation). Saturated fats are found in animal
foods like meat, poultry, and full-fat dairy products,
and in tropical oils such as palm and coconut.
Saturated vs. Unsaturated Fats
• Unsaturated fatty acid: a fatty acid with one or more
points of unsaturation. Unsaturated fats are found in
foods from both plant and animal sources. Unsaturated
fatty acids are further divided into monounsaturated fatty
acids and polyunsaturated fatty acids.
• Monounsaturated fatty acid: a fatty acid containing
one point of unsaturation, found mostly in vegetable oils
such as olive, canola, and peanut.
Saturated vs. Unsaturated Fats
• Polyunsaturated fatty acid:
(sometimes abbreviated PUFA) a fatty
acid in which two or more points of
unsaturation occur, found in nuts and
vegetable oils such as safflower,
sunflower, and soybean, and in fatty
fish.
Saturated vs. Unsaturated Fats
The Essential Fatty Acids
• The human body can synthesize all fatty acids
except:
 Linoleic acid, linolenic acid
Polyunsaturated fatty acids, essential for
human beings.
• Essential fatty acid
A fatty acid that cannot be synthesized in the
body in amounts sufficient to meet
physiological need.
Omega-6 vs. Omega-3 Fatty Acids
• Omega-3 fatty acids,
found in fish oils, offer
a protective effect on
health.
 Interest in fish oils first
kindled when someone
thought to ask why the
Eskimos of Greenland,
who eat a diet very high
in fat, have such a low
rate of heart disease.
 Blood clot formation,
inflammation (e.g.
arthritis, asthma),
irregular heart rhythm,
and cancer also seem to
be beneficially affected
by DHA and/ or EPA.
Something’s Fishy
Eating fish at least two times per week as
part of a balanced diet can:
 Reduce blood clot formation ( heart
attacks and strokes).
 Decrease risk of heart arrhythmias.
 Decrease blood triglycerides.
 Decrease atherosclerotic plaque formation.
 Improve health of arteries.
 Slightly lower blood pressure.
Characteristics of Fats in Foods
The more unsaturated a fat, the more liquid it is at room temperature.
The more polyunsaturated the fat is, the sooner it melts.
Characteristics of Fats in Foods
• Unsaturated fats are more likely to react with
oxygen and become rancid.
• Food manufacturers may alter fats and oils by:
 Hydrogenation
The process of adding hydrogen to
unsaturated fat to make it more solid and
more resistant to chemical change.
 Antioxidants
A compound that protects other compounds
from oxygen by itself reacting with oxygen.
 Emulsifiers
A substance that mixes with both fat and
water and can break fat globules into small
droplets, thereby suspending fat in water.
Other Members of the Lipid Family
A Phospholipid: Lecithin
Phospholipids…
 Important components of
cell membranes.
 Can serve as emulsifiers
in the body, joining with
both water and fat.
 Also used in foods such as
margarine, chocolate,
salad dressings, and
frozen desserts to keep
the fats dispersed.
 Widespread in foods.
Other Members of the Lipid Family
Sterols such as cholesterol
have a multiple-ring
structure.
Sterols such as cholesterol
• Incorporated as an
integral part of the
structure of cell
membranes.
• Used to make bile for
digestion.
• Used to make sex
hormones (estrogen and
testosterone).
• Made into vitamin D.
• Deposited in the artery
walls, leading to plaque
buildup and heart
disease.
Digestion of fat
A. Digestion of Fat
1. Mouth
Some hard fats begin to melt as
they reach body temperature.
Mouth
2. Stomach
The stomach’s churning
action mixes fat with water and
acid. A stomach enzyme
accesses and breaks apart a
small amount of fat. Fat is last to
leave the stomach.
3. Liver, Gallbladder, and
Liver
Small Intestine
Once in the small intestine, fat
encounters bile, an emulsifier
made in the liver (see Part B).
The gallbladder, a storage
organ, squirts bile into the
contents of the small intestine to
blend the fat with the watery
Gallbladder
digestive secretions.
4. Pancreas
Fat-digesting enzymes from the pancreas
(pancreatic lipase) enter the small
intestine. The enzymes can attack fat
only after emulsification by bile. They
break down the triglycerides to fatty
acids, glycerol, and monoglycerides.
5. Large intestine
Some fat and cholesterol, trapped in
fiber, are carried out of the body with
other wastes.
Salivary
glands
Stomach
Pancreas
Small
intestine
Large
intestine
How the Body Handles Fat
• The products of fat digestion are fatty acids,
glycerol, and monoglycerides.
 Monoglyceride
A glycerol molecule with one fatty acid attached
to it. A diglyceride is a glycerol molecule with
two fatty acids attached to it.
• The shortest fatty acids and glycerol pass by
simple diffusion into the absorptive cells and
without further processing can enter the blood
stream, travel to the liver, and be converted and
used by the body.
How the Body Handles Fat
• Bile
A mixture of compounds, including
cholesterol, made by the liver, stored in
the gallbladder, and secreted into the
small intestine. Bile emulsifies lipids to
ready them for enzymatic digestion and
helps transport them into the intestinal
wall cells.
How the Body Handles Fat
• Long-chain fatty acids, phospholipids, and
cholesterol are insoluble in water and
cannot be accepted by the body’s blood
and lymph system.
 Lymph
The body fluid that transports the products of fat
digestion toward the heart and eventually drains
back into the bloodstream.
• Lymph consists of the same components as
blood with the exception of red blood cells.
• These fats must be packaged into one of
four types of lipoproteins for transport.
How the Body Handles Fat
•
Lipoproteins
Clusters of lipids associated with protein that
serve as transport vehicles for lipids in blood
and lymph. The four main types of lipoproteins
are:
1.
Chylomicron
A type of lipoprotein that transports newly digested
fat—mostly triglyceride—from the intestine through
lymph and blood.
2. VLDL (very-low-density lipoprotein)
Carries fats packaged or made by the liver to various
tissues in the body.
3. LDL (low-density lipoprotein)
Carries cholesterol (much of it synthesized in the liver)
to body cells. A high blood cholesterol level usually
reflects high LDL.
4. HDL (high-density lipoprotein)
Carries cholesterol in the blood back to the liver for
recycling or disposal.
C. Absorption of Fat: The Chylomicron
Most of the newly digested fats are absorbed into lymph as
part of a special package—the chylomicron. A chylomicron
(lipoprotein) contains an interior of triglycerides and
cholesterol surrounded by phospholipids.
Proteins cover the
Phospholipid
Cholesterol
structure. Such an
Protein
arrangement of
Triglyceride
hydrophobic (waterfearing) molecules
(the fatty acids) on
the inside and
hydrophilic (waterloving)
molecules
(proteins) on the
outside allows lipids
to travel through the
watery fluids of the
body.
A. Functions and Interactions of Lipoproteins
Small intestine
Newly digested fats
are transported by
chylomicrons.
Chylomicron
VLDL
VLDL makes
fats available to
body cells via
enzyme action.
Lipids processed or made in
The liver are released in VLDL.
Remnants of
chylomicron
return to liver.
Liver
LDL (derived from VLDL)
carriesfats (mostly
LDL
cholesterol) to
body cells. LDL travels
through blood vessels,
is vulnerable to attack by
oxygen, and has affinity for
linings of artery walls—contributing
to plaque buildup.
HDL
HDL transports
cholesterol from
body cells back
to liver for recycling
or disposal.
Fat is made available to body
cells via enzyme action;
afterward, the remnants of
the chylomicron are returned
to the liver.
(Cholesterol)
Body cells
“Good” vs. “Bad” Cholesterol
• ATHEROSCLEROSIS: As LDL particles
penetrate the walls of the arteries, they
become oxidized-LDL and next are
scavenged by the body’s white blood
cells.
• These foam cells are then deposited into
the lining of the artery wall.
• This process, known as atherosclerosis,
causes plaque deposits to enlarge, artery
walls to lose elasticity, and the passage
through the artery to narrow.
“Good” vs. “Bad” Cholesterol
• Oxidized LDL-cholesterol
The cholesterol in LDLs that
is attacked by reactive
oxygen molecules inside the
walls of the arteries.
 Oxidized LDL is taken up
by scavenger cells and
deposited in plaque.
• Foam cells:
Cells from the immune
system containing
scavenged oxidized LDLcholesterol that are thought
to initiate arterial plaque
formation.
Atherosclerosis
Smooth muscle layer
Artery lining
Vessel
opening
Plaque
Normal artery
Early injury triggers
inflammation*
Oxidized LDL
Scavenger +
oxidized LDL
(incorporated
into lining
of artery as
Cholesterol
loaded foam
cell)
Atherosclerosis
White blood cell (scavenger)
LDL +
oxygen
White blood cell
Muscle cells
Accumulation of cholesterolloaded
foam cells—plaque formation
Fats Can Be Healthy
• Phytochemicals
 Physiologically
active compounds
found in plants
that appear to
help promote
health and reduce
risk for cancer,
heart disease, and
other conditions.
The
Mediterranean
food pyramid
Fats Can Be Healthy
• Use olive oil and other plant
oils that are rich in
monounsaturated and
polyunsaturated fats.
• Consume more omega-3 fats.
 Consider eating fish twice a week
as part of a balanced diet.
 Plant sources of omega-3 fats
include soybeans, flaxseed,
pecans, and walnuts.
• Consume a diet that is lower
in saturated fat and higher in
complex carbohydrates and
fiber.
 Include more fruits, vegetables,
whole-grain breads, and other
grains and legumes.
Fat Can Be Healthy
• One place to find omega-3 fats is
fish, especially fatty fish like
salmon.
• Nuts are rich in many nutrients
and other beneficial substances
but are also high in fat.
Trans Fatty Acid Controversy
• Trans fatty acid
A type of fatty acid created
when an unsaturated fat is
hydrogenated.
• Found primarily in
margarines, shortenings,
commercial frying fats,
and baked goods.
• Trans fatty acids have
been implicated in
research as culprits in
heart disease.
Trans Fat Controversy
Animal products
Candy: 1%
Breakfast cereal: 1%
Cakes, cookies, crackers,
pies, bread, etc.
21%
40%
Salad dressing: 3%
Household shortening: 4%
Potato chips, corn
chips, popcorn: 5%
17%
Fried potatoes: 8%
Margarine
Trans Fat Controversy
Compare spreads
In 2006, the Food and Drug Administration began
requiring that manufacturers list the trans fat
content on food labels.
Choose Fats Sensibly
Choose Fats Sensibly…
• Use nonstick sprays rather than fat
to coat pans.
• Try reducing the fat in recipes a
little at a time
• Try reducing fat in recipes a little
at a time and use nonstick sprays,
fat-free broth or wine in place of
butter or margarine.
• Refrigerate soups and broth, then
skim off the hardened fat.
• Prepare lean meats, trim visible
fats, remove poultry skin and cook
meats so that fats can drain off.
• Use herbs, spices, onions or garlic,
salsa, lemon juice, or mustard
instead of butter, margarine, or
oil. Experiment with substitutes.
Bake, broil, poach, or steam.
Season with herbs & spices.
Nourish the Heart
1. Become a savvy
supermarket
shopper.
2. Keep blood
cholesterol at or
below the
recommended
levels.
3. Balance energy
intake with energy
needs.
Checking Out the Food Label for Fat
Information
• Total fat refers to all the fat in the food:
saturated, monounsaturated,
polyunsaturated, and trans fat.
• Total fat, saturated fat, trans fat, and
cholesterol information are required on
the label.
• Listing the amount of monounsaturated
and polyunsaturated fats is voluntary.
Checking
out the
food label
for fat
information
Diet & Heart Disease
• More than half the people who die
in the U.S. each year die of heart
and blood vessel disease.
• Twin demons that lead to heart
disease are:
1. Atherosclerosis: narrowing of the
arteries caused by plaque build-up.
2. Hypertension: high blood pressure.
A normal artery provides
open passage for blood
to circulate.
Plaques along an artery
wall narrow the passage
and obstruct blood flow.
Leading Risk Factors for Heart Disease
• High LDL blood
• An “atherogenic” diet
cholesterol level
(high in saturated and
trans fats, & low in
• Low HDL blood
fruits, vegetables,
cholesterol level
legumes, & whole
• High blood pressure
grains)
• Cigarette smoking
• Other risk factors
• Obesity
cannot be changed:
• Physical inactivity
advanced age, male
gender, & family
• Diabetes
history
Diet and Heart Disease
• Eat a variety of antioxidant-rich fruits and
vegetables. Choose nine servings per day.
• Choose fat-free or low-fat dairy products, such
as fat-free milk or low-fat or fat-free yogurt.
Choose milk or yogurt more often than cheese
• Consume abundant legumes of many
varieties, including soybeans, kidney beans,
and lentils.
• Eat a variety of whole grains and other foods
high in soluble fibers and eat fewer refined
grain products.
• Choose soy foods, skinless poultry, lean meat, and
fish, especially fish such as salmon that is rich in
omega-3 fatty acids, in place of foods high in saturated
fat.
• Limit your intake of foods that are high in saturated fat
and trans fat, such as full-fat milk products, fatty
meats, tropical oils, and partially hydrogenated
vegetable oils.
• Limit your intake of foods that are high in calories from
solid fats and added sugars, such as cakes, cookies,
candy, and ice cream; pizza; cheese; processed and
fatty meats; and sweetened beverages.
• Adopt heart-healthy cooking methods, such as broiling,
baking, steaming, and stir-frying.
• Reduce daily sodium intake to less than 2,300
milligrams and further reduce intake to 1,500
milligrams if you are 51 or older, African American, or
have high blood pressure or diabetes.
• Get more potassium in your diet from foods such as
cantaloupe, bananas, beans, and yogurt.
• Consume alcohol only in moderation, if at all. Have no
more than one alcoholic drink per day if you’re a
woman and no more than two if you’re a man. “One
drink” means it has no more than 1⁄2 oz of pure
alcohol. Examples of one drink are 12 oz of beer, 5 oz
of wine, 11⁄2 oz of 80-proof spirits, or 1 oz of 100proof spirits.