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Dietary Fats Are Not Created Equal |
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Copyright 2005 Kristy Haugen
Understanding the different types of fats can be difficult for
the consumer. Since not all fats are created equal in health, it
is important to understand the differences in dietary fats;
healthy versus unhealthy.
Triglycerides (triacylglycerols) are an important class of
dietary fats. The triglyceride consists of a molecule of
glycerol and three molecules of fatty acids. Biologic properties
of triglycerides are determined by the presence or absence of
double bonds, the number and location of double bonds, and the
configuration (cis, trans) of the unsaturated fatty acid. Fatty
acids consist of a hydrocarbon chain (C-H) with a carboxyl group
(COOH) at one end. The glycerol molecule contains three hydroxyl
groups (OH).
Much of the fat in the body is in the form of triglycerides.
Many of the foods we eat also contain triglycerides. Elevated
triglyceride levels in the blood have been linked to an
increased risk of heart disease. These triglycerides are not
directly from dietary fats but made in the liver from excess
sugars that have not been used for energy. The excess sugar
source is from foods containing carbohydrates such as refined
sugar and white flour.
Saturated fats are a type of triglyceride. This triglyceride
contains primarily fatty acids whose side chains do not contain
any double bonds. These fats are characteristically called
saturated because all available carbon bonds are occupied by a
hydrogen atom. Saturated fats are highly stable and can resist
oxidation. The saturated fat molecule is straight in form.
Hence, saturated fats form a solid or semisolid at |
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room
temperature. Main sources of saturated fats are meat and dairy
products, and a few vegetable oils (palm and coconut oils). A
diet high in saturated fat is associated with an increased risk
of heart disease.
Monounsaturated fats are another type of triglyceride. The fatty
acids contain only one double bond. A few sources of
monounsaturated fats are olive, peanut, and rapeseed (canola)
oil. This type of fat has the ability to favorably modify
lipoprotein levels. A good example of a diet high in
monounsaturated fat is the Mediterranean diet. The Mediterranean
cultures show that a diet rich in olive oil is correlated with a
low incidence of heart disease.
Polyunsaturated fats are a type of triglyceride in which the
fatty acids contain more than one double bond. Double bonds in
natural fats are rigid and introduce a kink in the molecule.
This kink prevents the fatty acids from packing close together.
As a result, unsaturated fats have a lower melting point than
saturated fats. Most unsaturated fats are liquid at room
temperature and referred to as oils.
The effect that the polyunsaturated fat has on heart disease is
influenced by the location of the double bond within the
molecule. Omega-6 fatty acids (n-6 fatty acids) are a type of
polyunsaturated fat. The omega-6 fatty acid, primarily linoleic
acid obtained from vegetable oils protects against heart
disease. Good sources of omega-6 fats are nuts, avocados,
olives, soybeans, along with sesame, cottonseed, and corn oil.
Omega-3 fatty acids (n-3 fatty acids) are a type of
polyunsaturated fat. The omega-3 fatty acid is primarily
linolenic acid. These fatty |
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