Although much attention has been focused on the need to
reduce dietary fat, the body does need fat. During infancy and childhood, fat is necessary
for normal brain development. Throughout life, it is essential to provide energy and
support growth. Fat is, in fact, the most concentrated source of energy available to the
body. However, after about two years of age, the body requires only small amounts of
fat-much less than is provided by the average American diet. Excessive fat intake is a
major causative factor in obesity, high blood pressure, coronary heart disease, and colon
cancer, and has been linked to a number of other disorders as well. To understand how fat
intake is related to these health problems, it is necessary to understand the different
types of fats available and the ways in which these fats act within the body.
Fats are composed of building blocks called fatty acids.
There are three major categories of fatty acids-saturated, polyunsaturated, and
monounsaturated. These classifications are based on the number of hydrogen atoms in the
chemical structure of a given molecule of fatty acid.
acids are found primarily in animal
products, including dairy items, such as whole milk, cream, and cheese, and fatty meats
like beef, veal, lamb, pork, and ham. The fat marbling you can see in beef and pork is
composed of saturated fat. Some vegetable products including coconut oil, palm kernel oil,
and vegetable shortening-are also high in saturates.
The liver uses saturated fats to manufacture cholesterol.
Therefore, excessive dietary intake of saturated fats can significantly raise the blood
cholesterol level, especially the level of low-density lipoproteins (LDLs), or "bad
cholesterol. " Guidelines issued by the National Cholesterol Education Program
(NCEP), and widely supported by most experts, recommend that the daily intake of saturated
fats be kept below 10 percent of total caloric intake. However, for people who have severe
problems with high blood cholesterol, even that level may be too high.
fatty acids are found in greatest
abundance in corn, soybean, safflower, and sunflower oils. Certain fish oils are also high
in polyunsaturated fats. Unlike the saturated fats, polyunsaturated fats may actually lower your
total blood cholesterol level. In doing so, however, large amounts of
polyunsaturated fats also
have a tendency to reduce your high-density lipoproteins (HDLs)-your .good
cholesterol." For this reason-and because, like all fats, polyunsaturated
fats are high in
calories for their weight and volume-the NCEP guidelines state that an individual's intake
of polyunsaturated fats should not exceed 10 percent of total caloric intake.
fatty acids are found mostly in
vegetable and nut oils such as olive, peanut, and canola. These fats appear to reduce
blood levels of LDLs without affecting HDLs in any way. However, this positive impact upon
LDL cholesterol is relatively modest. The NCEP guidelines recommend that intake of
monounsaturated fats be kept between 10 and 15 percent of total caloric intake.
Although most foods-including some plant-derived foods
contain a combination of all three types of fatty acids, one of the types usually
predominates. Thus, a fat or oil is considered 'saturated" or "high in
saturates' when it is composed primarily of saturated fatty acids. Such saturated fats are
usually solid at room temperature. Similarly, a fat or oil composed mostly of
polyunsaturated fatty acids is called "polyunsaturated," while a fat or oil
composed mostly of monounsaturated fatty acids is called "monounsaturated."
One other element, trans-fatty acids, may also play a role in blood cholesterol levels. Also called trans
fats, these substances occur when polyunsaturated oils are altered through hydrogenation,
a process used to harden liquid vegetable oils into solid foods like margarine and
shortening. One recent study found that trans-monounsaturated fatty acids raise LDL
cholesterol levels, behaving much like saturated fats. Simultaneously, the trans-fatty
acids reduced HDL cholesterol readings. Much more research on this subject is necessary,
as studies have not reached consistent and conclusive findings. For now, however, it is
clear that if your goal is to lower cholesterol, polyunsaturated and
are more desirable than saturated fats or products with trans-fatty acids. just as
important, your total calories from fat should not constitute more than 20 to 25 percent
of daily calories.
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