What You Should
Know About Triglycerides and Fatty Acids
Elisabeth Schafer, Ph.D. Extension Nutrition Specialist
Diane Nelson. Extension Communications Specialist
Iowa State University
Triglycerides = "fat"
Triglycerides form one of the
five types of lipids or fats that occur in living things. The others are
* sterols (cholesterol, some
hormones);
* fat-soluble vitamins (A,E,K);
* sphingolipids (components of
cell membranes) and;
* fatty acids (saturated or
unsaturated).
Thus, cholesterol and fats are
not the same thing. Although they are related, they are completely different
in chemical structure and behavior in the body.
Triglycerides include such
substances as body fat, cooking oil, lard, butter, and beef fat. As found in
the blood stream, triglycerides are fats being transported from intestines to
body cells. They may originate from foods or be manufactured within the body.
Chemical definition of
triglycerides
A molecule of triglyceride is
composed of a backbone of glycerol to which three fatty acids
("tri") are bound. Any combination of saturated, monounsaturated, or
polyunsaturated fatty acids can be in a triglyceride molecule.
A good way to envision a
triglyceride molecule is to look at your hand. Hold out the three center
fingers and fold back the thumb and little finger. The three fingers are the
three fatty acids and your hand is the glycerol. As the three fingers are
different, so the three fatty acids in a triglyceride can be different. The
fatty acids can be long or short, saturated (stiff) or unsaturated (bendable).
The fatty acids may bend at different locations along the chain Just as the
space between knuckles may differ.
Ingredient labels on foods such
as bread or breakfast cereals often list mono- and diglycerides. These are
glycerol backbones with only one (mono-) or two (di-) fatty acids attached.
They are added to foods to prolong freshness.
What are fatty acids?
Fatty acids are long chains of
carbon atoms with an acid group at one end and a methyl group at the other
end. The length of the carbon chain may vary from 4 to more than 20 carbon
atoms. Fatty acids in foods, plasma triglycerides, and body fat typically have
16 to 20 carbon atoms. These fatty acids are not water soluble. The fatty
acids in fish oils are generally 20 to 22 carbon atoms long. Table 1 gives
information about eight important fatty acids.
Saturated or unsaturated?
Hydrogen can be attached to
these carbon atom chains. If each carbon atom is bound to as many hydrogen
atoms as is chemically possible, it is saturated" (no more hydrogen can
be added). A monounsaturated fatty acid has one site where hydrogen atoms can
be added. A polyunsaturated fatty acid has two or more sites for additional
hydrogen atoms.
Table 1. Important fatty acids.
Name Type Food sources
-------------------------------------------------------------------------------------------------------
Palmitic saturated beef fat, palm and palm kernel oil, butter, lard
Stearic saturated beef fat
Oleic monounsaturated (omega-9) olive oil, canola oil
Linoleic* polyunsaturated (omega-6) soybean oil, safflower oil, corn oil
Linolenic* polyunsaturated (omega-3) soybean oil, canola oil
Arachidonic* polyunsaturated (omega-6) -
Eicosapentaenoic polyunsaturated (omega-3) fish oils
Docosahexaenoic polyunsaturated (omega-3) fish oils
-----------------------------------------------------------------------------------------------------
*essential fatty acids
Saturated, monounsaturated, and
polyunsaturated fatty acids all have the same calorie content and are used
similarly for energy in the body However, the difference in hydrogen content
makes a difference in their physical properties.
The saturated fatty acid is a
rigid chain. At room temperature it is a solid.
The polyunsaturated fatty acid
is a chain with missing" hydrogens; these gaps act as hinges, permitting
the fatty acid to bend. A polyunsaturated fatty acid is flexible. At room
temperature polyunsaturated fatty acids are liquids.
Location of gaps affects
function
Omega-3 means the first
unsaturated site, or gap, on the carbon chain is three carbons from the methyl
or omega end. The omega-3 fatty acids cannot be made by humans but are
abundant in fish and soybean oil.
Omega-6 fatty acids cannot be
made by humans and are considered essential in the diet. Omega-6 fatty acids
are common in corn oil, soybean oil, safflower oil, and many other foods. The
essential fatty acids are incorporated into cell membranes and are used to
make localized hormones called prostaglandins and leukotrienes which regulate
blood clotting, muscle contractions, and immune responses.
Omega-3 fatty acids compete
with omega-6 fatty acids to perform these functions. In some cases the
prostaglandins and leukotrienes made from omega-3 fatty acids are more
effective and in others less effective than the omega-6 forms. Omega-9 fatty
acids, with the first unsaturated site 9 carbons away from the methyl end, can
be made in our bodies and are common in olive oil, peanuts, avocado, and
canola oils. Omega-9 fatty acids cannot substitute for the essential omega-6
fatty acids in body functions.
Fatty acids in foods
Most dietary fats, as well as
body fat, are combinations of all three types of fatty acids. If the fat is
hard, the majority of fatty acids on the triglycerides are saturated. If the
fat is liquid, the majority of fatty acids on the triglycerides are
polyunsaturated. Table 2 shows how three common food fats compare.
Table 2. Percentage of fatty
acids in common fats.
Butter Coconut Soybean
oil oil
--------------------------------------------
Saturated 51 87 14
Monounsaturated 23 6 23
Polyunsaturated 3 2 58
--------------------------------------------
Source: USDA Handbook 8-4, Composition of Foods, 1979.
Hydrogenation and trans fatty
acids
Polyunsaturated fatty acids can
be converted to saturated fatty acids by adding hydrogen. This is called
hydrogenation.
During hydrogenation the fatty
acids may be twisted at the site where hydrogen is added. The natural
structure for a fatty acid is "cis." The hydrogenated fatty acid
that has been distorted is "trans."
Despite rumors to the contrary,
trans fatty acids are probably not harmful to health. Laboratory rats fed high
levels of trans fatty acids had normal lifespan, normal reproduction, and
appeared healthy in every way. Early studies in humans linked trans fatty
acids to elevated serum cholesterol. However, the studies had serious flaws
making their results questionable.
Plasma triglycerides and heart
disease
The evidence linking elevated
blood triglyceride levels with cardiovascular disease is less compelling than
the evidence linking elevated blood cholesterol. Plasma triglycerides are
correlated with cardiovascular disease but the association can be almost
entirely explained by the fact that triglycerides are carried on LDL (low
density lipoprotein) and its metabolic precursor VLDL (very low density
lipoprotein). Furthermore, there is an inverse relationship between
concentrations of triglyceride and high density lipoprotein (HDL). When
triglyceride levels are low, HDL levels are high. When triglyceride levels are
high, HDL is low. Thus plasma triglyceride concentration is probably not an
independent risk factor.
Desirable plasma triglyceride
levels are 40 to 150 mg/dL. Some medications can raise plasma triglycerides.
Omega-3 fatty acids and fish oil
Recent research has shown the
omega-3 fatty acids in fish oil can be effective in lowering elevated plasma
triglyercides. However, the quantity of fish oil needed is large and there
could a undesirable side effects such as altered immune response,
hemorrhaging, and vitamin E deficiency. For these reasons you may safely eat
fish twice a week but should use fish oil capsules only under a physician's
supervision.
In general cold water marine
fish, such as mackerel, salmon and herring, have more omega-3 fatty acids than
fish from fresh water or warmer waters, such as trout, catfish, halibut, and
tuna.
Recommended diet
The diet usually recommended
for lowering high triglycerides is low in calories, fat, saturated fat, sugar,
and alcohol. Your body makes triglycerides from the fats and carbohydrates you
eat. Triglycerides are made when cells have an abundance of energy and need to
store it.
The diet for lowering blood
triglycerides is almost identical to the recommendations for lowering blood
cholesterol or losing weight, Table 4 shows how following dietary
recommendations can affect health conditions.
Table 4, Common dietary
recommendations for health risks.
Elevated blood Elevated blood
cholesterol triglycerides Overweight
--------------------------------------------------------------------------------
Reduce calories x x x
Reduce saturated fat x x
Reduce total fat x x x
Reduce sugar x x
Reduce cholesterol x
Increase soluble fiber x x
Reduce alcohol x x x
--------------------------------------------------------------------------------
Quiz
Here's a quiz to check what you
know about triglycerides and fatty acids.
T F 1. All vegetable fats are polyunsaturated.
T F 2. Tub margarine is probably less saturated than stick margarine.
T F 3. A triglyceride is a type of lipoprotein.
T F 4. Desirable blood triglyceride level is 200 mg/dL.
T F 5. Some fatty acids are essential in the diet.
Answers
1. False. Coconut, palm, and
palm kernel oils are primarily saturated.
2. True. The softer the fat the
more polyunsaturated fatty acids it usually contains.
3. False. Triglyceride is fat:
three fatty acids bound to a molecule of glycerol.
4. False. The desirable range
is 40-150 mg/dL.
5. True. Some omega-3 and
omega-6 fatty acids are considered essential since the human body cannot
manufacture them. At least 3 percent of calories each day should be linoleic
acid.
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