Section 1
Fundamentals of Nutrition
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Chapter 5
Lipids, or Fats
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Objectives
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State the functions of fats in the body
Identify sources of dietary fats
Explain common classifications of fats
Describe disease conditions with which
excessive use of fats is associated
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Facts
Fats belong to a group of organic
compounds called lipids.
Greasy substances that are insoluble in
water.
Each gram of fat contains 9 kcal.
Composed of carbon, hydrogen, and
oxygen; lower proportion of oxygen than
carbohydrates.
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Functions
Provide energy
Carry fat-soluble vitamins
Supply essential fatty acids
Protect and support organs and bones
Insulate from cold
Provide satiety to meals
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Food Sources
Animal
Plant
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Fatty meats
Lard
Butter
Cheese
Cream; whole
milk
Egg yolk
Vegetable oils
Nuts
Chocolate
Avocados
Olives
Margarine
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Visible and Invisible Fats
Visible fats
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Fats in foods
that are
purchased and
used as fats,
such as butter or
margarine, lard,
cooking oils
Invisible fats
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Fats that are not
immediately
noticeable such
as those in egg
yolk, cheese,
cream, and
salad dressings
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Stop and Share
You are the nurse teaching a class about
nutrition.
A client asks about ways to decrease the
amount of fat in the diet.
What are some suggestions you can give?
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Stop and Share
Beware of hidden fats!
Decrease the amount of fatty meats
(bacon, sausage, luncheon meats) and use
lean meats instead.
Use low-fat or skim milk.
Use egg whites instead of yolks when
possible. (Egg white contains no fat; it is
almost entirely protein and water.)
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Classification
Triglycerides
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Most lipids in the body (95%) are
triglycerides
Composed of three fatty acids attached to
a framework of glycerol
Phospholipids
Sterols
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Cholesterol
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Fatty Acids
Fatty acids are organic compounds of
carbon atoms to which hydrogen atoms are
attached.
They may be classified in two ways.
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Fatty Acid Classification
May be classified by the body’s need for
them
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Essential
Nonessential
May be classified by degree of saturation
with hydrogen atoms
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Saturated
Unsaturated
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Monounsaturated
Polyunsaturated
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Essential Fatty Acids
Cannot be synthesized by the body
Must be obtained from the diet
Types
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Linoleic acid
Linolenic acid
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Non-essential Fatty Acids
Can be synthesized by the body
Arachidonic fatty acid, previously thought
to be essential, can be synthesized in the
body from linoleic fatty acid.
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Saturated Fats
Each of its carbon atoms carries all the
hydrogen atoms possible.
In general, animal foods contain more
saturated fatty acids than unsaturated.
Usually solid at room temperature.
Examples: Meat, poultry, egg yolks,
whole milk, whole milk cheeses, cream,
ice cream, butter, chocolate, coconut, palm
oil
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Monounsaturated Fats
Fewer hydrogen atoms attached to one
place among the carbon atoms of its fatty
acids than saturated fats.
Lowers low-density lipoprotein (LDL or
“bad cholesterol”).
Examples: Olive oil, canola oil, avocados,
cashew nuts
Recommended: 15% of total daily kcal
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Polyunsaturated Fats
Fewer hydrogen atoms attached to two or
more places among the carbon atoms of its
fatty acids than saturated fats.
Examples: Cooking oils made from
sunflower, safflower, sesame seeds or from
corn or soybeans, soft margarines whose
major ingredient is liquid vegetable oil,
and fish
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Polyunsaturated Fats
Foods containing high proportions of
polyunsaturated fats are usually soft or
oily.
Omega-3 fatty acids (found in fish) lower
the risk of heart disease.
Omega-6 (linoleic acid) has a cholesterollowering effect.
Recommended: 10% of total daily kcal
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Hydrogenated Fats
Polyunsaturated vegetable oils to which
hydrogen has been added commercially to
make them solid at room temperature.
This process, called hydrogenation, turns
polyunsaturated vegetable oils into
saturated fats.
Margarine is made in this way.
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Trans-Fatty Acids (TFAs)
Produced when hydrogen atoms are added
to monounsaturated or polyunsaturated fats
to produce a semi-solid product like
margarine and shortening.
TFAs raise low-density lipoproteins (LDL)
and total cholesterol.
Major source: baked goods and restaurant
foods
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Phospholipid
Found in both plant and animal foods, and
is synthesized in the liver.
Natural emulsifier that helps transport fat
in the bloodstream.
Example: Lecithin
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Cholesterol
Cholesterol is a sterol
Fatlike substance
Exists in animal foods and body cells
Does not exist in plant foods
Essential for the synthesis of bile, sex
hormones, cortisone, and vitamin D
Needed by every cell in the body
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Stop and Share
Your client has been diagnosed with a high
cholesterol level greater than 200 mg/dl.
Answer the following questions:
What risks are associated with a high
cholesterol level?
What can be done to lower a high
cholesterol level?
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Stop and Share
High cholesterol leads to atherosclerosis, a
cardiovascular disease in which plaque
(fatty deposits containing cholesterol and
other substances) forms on the inside of
artery walls. This can lead to heart
attacks and strokes.
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Stop and Share
Reduce the amount of total fat,
saturated fats, and cholesterol.
Increase monounsaturated fats in the
diet, lose weight and exercise.
Increase consumption of soluble
dietary fiber. Medication may be
prescribed in some cases. Daily
cholesterol intake should not exceed
300 mg.
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Digestion and Absorption
95% of ingested fats are digested
Complex process
Chemical digestion of fats occurs mainly
in the small intestine
No digestion of fats occurs in the mouth
Slight digestion in stomach where gastric
lipase acts on emulsified fats such as those
found in cream and egg yolk.
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Digestion and Absorption
Digestion in the small intestine
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Bile emulsifies the fats
The enzyme pancreatic lipase reduces the
fats to fatty acids and glycerol
The body subsequently absorbs through
the villi of the small intestine
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Digestion and Absorption
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Lipoproteins
In the initial stages of fat absorption, bile
joins with the products of fat digestion to
carry fat.
Later, protein combines with the final
products of fat digestion to form special
carriers called lipoproteins.
Lipoproteins carry the fat in the blood to
the body cells.
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Lipoproteins
Classified according to mobility and
density
Types
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Chylomicrons
Very-low-density lipoproteins (VLDLs)
Low-density lipoproteins (LDLs)
High-density lipoproteins (HDLs)
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Chylomicron
First lipoprotein identified after eating
Largest lipoprotein
Lightest in weight
Composed of 80-90% triglycerides
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Very-low-density Lipoproteins
(VLDLs)
Made by the liver to transport lipids
throughout the body.
Composed of 55-65% triglycerides.
Carry triglycerides and other lipids to all
cells.
As the VLDL lose triglycerides, they pick
up cholesterol from other lipoproteins in
the blood and they then become LDL.
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Low-density Lipoproteins (LDLs)
Composed of 45% cholesterol with few
triglycerides.
Carry most of the blood cholesterol from
the liver to the cells.
Elevated blood levels greater than 130
mg/dl of LDL are thought to be
contributing factors in atherosclerosis.
“Bad cholesterol”
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High-density Lipoproteins
(HDLs)
Carry cholesterol from the cells to the liver
for eventual excretion.
Levels of HDL greater than 35 mg/dl are
thought to reduce the risk of heart disease.
Exercise, maintaining a desirable weight,
and giving up smoking are all ways to
increase one’s HDL.
“Good cholesterol”
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Metabolism and Elimination
The liver controls fat metabolism.
The metabolism of fats occurs in the cells.
Fatty acids are broken down to carbon
dioxide and water, releasing energy.
Portion of fat not needed for immediate
use stored as adipose tissue.
Carbon dioxide and water are waste
products removed from the body by the
circulatory, respiratory, and excretory
systems.
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Stop and Share
Your client asks you about a new dietary
supplement that advertisers claim provides
essential nutrients and lowers cholesterol
“naturally”.
How do you advise your client?
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Stop and Share
Any new dietary “supplement” for which a
nutrition claim is made should be carefully
evaluated.
If the item is not included in the RDA or DRI,
it is safe to assume that medical research has
not determined that it is essential.
Ingestion of dietary supplements of unknown
value could, ironically, be damaging to one’s
health.
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Fat Alternatives
Olestra: Made from carbohydrates and fat
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FDA approved for use in snack food
Government requires that food labels
indicate olestra “inhibits absorption of
some vitamins and other nutrients”
Contains no calories; can cause cramps
and diarrhea
Simplesse: Made from egg white or milk
protein
Oatrim: Carbohydrate-based; derived
from
oat
fiber
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Dietary Requirements
The Food and Nutrition Board’s
Committee on Diet and Health
recommends that people reduce their fat
intake to 30% of total kcal.
American Heart Association’s newest
recommendation is to consume </=7% of
saturated fats, 8-10% polyunsaturated fats
and 15% monounsaturated fats.
At present, 36% of kcal in U.S. diets is
derived from fats.
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Conclusion
Fats provide energy, carry essential fatty
acids and fat-soluble vitamins, protect
organs and bones, insulate from cold, and
provide satiety to meals.
Composed of carbon, hydrogen, and
oxygen and are found in both animal and
plant foods.
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Conclusion
Each gram of fats provides 9 kcal.
Digestion occurs primarily in small
intestines.
An excess of fat in the diet can result in
obesity and possible heart disease or
cancer.
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