Triglycerides and VLDL
Triglyceride is another form in which fat is transported
through the blood to the body tissues. Most of the body's stored
fat is in the form of triglycerides. Another lipoprotein--very low-
density lipoprotein, or VLDL--has the job of carrying triglycerides
in the blood. NHLBI considers a triglyceride level below 250 mg/dl
to be normal.
It is not clear whether high levels of triglycerides alone
increase an individual's risk of heart disease. However, they may
be an important clue that someone is at risk of heart disease for 
other reasons. Many people who have elevated triglycerides also
have high LDL-cholesterol or low HDL-cholesterol. People with
diabetes or kidney disease--two conditions that increase the risk
of heart disease--are also prone to high triglycerides.
Dietary Fat and Cholesterol Levels
Many people are confused about the effect of dietary fats on
cholesterol levels. At first glance, it seems reasonable to think
that eating less cholesterol would reduce a person's cholesterol
level. In fact, eating less cholesterol has less effect on blood
cholesterol levels than eating less saturated fat. However, some
studies have found that eating cholesterol increases the risk of
heart disease even if it doesn't increase blood cholesterol levels.
Another misconception is that people can improve their
cholesterol numbers by eating "good" cholesterol. In food, all
cholesterol is the same. In the blood, whether cholesterol is
"good" or "bad" depends on the type of lipoprotein that's carrying
it.
Polyunsaturated and monounsaturated fats do not promote the
formation of artery-clogging fatty deposits the way saturated fats
do. Some studies show that eating foods that contain these fats can
reduce levels of LDL-cholesterol in the blood. Polyunsaturated
fats, such as safflower and corn oil, tend to lower both HDL- and
LDL-cholesterol. Edible oils rich in monounsaturated fats, such as
olive and canola oil, however, tend to lower LDL-cholesterol
without affecting HDL levels.
How Do We Know Fat's a Problem?
In 1908, scientists first observed that rabbits fed a diet of
meat, whole milk, and eggs developed fatty deposits on the walls of
their arteries that constricted the flow of blood. Narrowing of the
arteries by these fatty deposits is called atherosclerosis. It is a
slowly progressing disease that can begin early in life but not
show symptoms for many years. In 1913, scientists identified the
substance responsible for the fatty deposits in the rabbits'
arteries as cholesterol.
In 1916, Cornelius de Langen, a Dutch physician working in
Java, Indonesia, noticed that native Indonesians had much lower
rates of heart disease than Dutch colonists living on the island.
He reported this finding to a medical journal, speculating that the
Indonesians' healthy hearts were linked with their low levels of
blood cholesterol.
De Langen also noticed that both blood cholesterol levels and
rates of heart disease soared among Indonesians who abandoned their
native diet of mostly plant foods and ate a typical Dutch diet
containing a lot of meat and dairy products. This was the first
recorded suggestion that diet, cholesterol levels, and heart
disease were related in humans. But de Langen's observations lay
unnoticed in an obscure medical journal for more than 40 years.
After World War II, medical researchers in Scandinavia noticed
that deaths from heart disease had declined dramatically during the
war, when food was rationed and meat, dairy products, and eggs were
scarce. At about the same time, other researchers found that people
who suffered heart attacks had higher levels of blood cholesterol
than people who did not have heart attacks.
Since then, a large body of scientific evidence has been
gathered linking high blood cholesterol and a diet high in animal
fats with an elevated risk of heart attack. In countries where the
average person's blood cholesterol level is less than 180 mg/dl,
very few people develop atherosclerosis or have heart attacks. In
many countries where a lot of people have blood cholesterol levels
above 220 mg/dl, such as the United States, heart disease is the
leading cause of death.
High rates of heart disease are commonly found in countries
where the diet is heavy with meat and dairy products containing a
lot of saturated fats. However, high-fat diets and high rates of
heart disease don't inevitably go hand-in-hand.
Learning from Other Cultures
People living on the Greek island of Crete have very low rates
of heart disease even though their diet is high in fat. Most of
their dietary fat comes from olive oil, a monounsaturated fat that
tends to lower levels of "bad" LDL-cholesterol and maintain levels
of "good" HDL-cholesterol.
The Inuit, or Eskimo, people of Alaska and Greenland also are
relatively free of heart disease despite a high-fat, high-
cholesterol diet. The staple food in their diet is fish rich in
omega-3 polyunsaturated fatty acids.
Some research has shown that omega-3 fatty acids, found in
fish such as salmon and mackerel as well as in soybean and canola
oil, lower both LDL-cholesterol and triglyceride levels in the
blood. Some nutrition experts recommend eating fish once or twice a
week to reduce heart disease risk. However, dietary supplements
containing concentrated fish oil are not recommended because there
is insufficient evidence that they are beneficial and little is
known about their long-term effects.
Omega-6 polyunsaturated fatty acids have also been found in
some studies to reduce both LDL- and HDL-cholesterol levels in the
blood. Linoleic acid, an essential nutrient (one that the body
cannot make for itself) and a component of corn, soybean and
safflower oil, is an omega-6 fatty acid.
At one time, many nutrition experts recommended increasing
consumption of monounsaturated and polyunsaturated fats because of
their cholesterol-lowering effects. Now, however, the advice is
simply to reduce dietary intake of all types of fat. (Infants and
young children, however, should not restrict dietary fat.)
The available information on fats may be voluminous and is
sometimes confusing. But sorting through the information becomes
easier once you know the terms and some of the history.
The "bottom line" is actually quite simple, according to John
E. Vanderveen, Ph.D., director of the Office of Plant and Dairy
Foods and Beverages in FDA's Center for Food Safety and Applied
Nutrition. What we should be doing is removing as much of the
saturated fat from our diet as we can. We need to select foods that
are lower in total fat and especially in saturated fat." In a
nutshell, that means eating fewer foods of animal origin, such as
meat and whole-milk dairy products, and more plant foods such as
vegetables and grains. n
Eleanor Mayfield is a writer in Silver Spring, Md.
Fat Words
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