All About Fat & Cholesterol


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All About Fats & Cholesterol

 

Once upon a time, we didn't know anything about fat except that it made
foods tastier. We cooked our food in lard or shortening. We spread butter on
our breakfast toast and plopped sour cream on our baked potatoes. Farmers
bred their animals to produce milk with high butterfat content and meat
"marbled" with fat because that was what most people wanted to eat.

But ever since word got out that diets high in fat are related to heart
disease, things have become more complicated. Experts tell us there are
several different kinds of fat, some of them worse for us than others. In
addition to saturated, monounsaturated and polyunsaturated fats, there are
triglycerides, trans fatty acids, and omega 3 and omega 6 fatty acids.

Most people have learned something about cholesterol, and many of us
have been to the doctor for a blood test to learn our cholesterol
"number." Now, however, it turns out that there's more than one
kind of cholesterol, too.

Almost every day there are newspaper reports of new studies or
recommendations about what to eat or what not to eat: Lard is bad, olive oil
is good, margarine is better for you than butter-- then again, maybe it's
not.

Amid the welter of confusing terms and conflicting details, consumers
are often baffled about how to improve their diets. FDA recently issued new
regulations that will enable consumers to see clearly on a food product's
label how much and what kind of fat the product contains. (See "A Little
Lite Reading" in the June 1993 FDA Consumer.) Understanding the terms
used to discuss fat is crucial if you want to make sure your diet is within
recommended guidelines (see accompanying article).

Fats and Fatty Acids

Fats are a group of chemical compounds that contain fatty acids. Energy
is stored in the body mostly in the form of fat. Fat is needed in the diet to
supply essential fatty acids, substances essential for growth but not
produced by the body itself.

There are three main types of fatty acids: saturated, monounsaturated
and polyunsaturated. All fatty acids are molecules composed mostly of carbon
and hydrogen atoms. A saturated fatty acid has the maximum possible number of
hydrogen atoms attached to every carbon atom. It is therefore said to be
"saturated" with hydrogen atoms.

Some fatty acids are missing one pair of hydrogen atoms in the middle
of the molecule. This gap is called an "unsaturation" and the fatty
acid is said to be "monounsaturated" because it has one gap. Fatty
acids that are missing more than one pair of hydrogen atoms are called
"polyunsaturated."

Saturated fats (which contain saturated fatty acids) are mostly found
in foods of animal origin. Monounsaturated and polyunsaturated fats (which
contain monounsaturated and polyunsaturated fatty acids) are mostly found in
foods of plant origin and some seafoods. Polyunsaturated fatty acids are of
two kinds, omega-3 or omega-6. Scientists tell them apart by where in the
molecule the "unsaturations," or missing hydrogen atoms, occur.

Recently a new term has been added to the fat lexicon: trans fatty
acids. These are by products of partial hydrogenation, a process in which
some of the missing hydrogen atoms are put back into polyunsaturated fats.
"Partially hydrogenated vegetable oils," such as vegetable
shortening and margarine, are solid at room temperature.

Cholesterol

Cholesterol is sort of a "cousin" of fat. Both fat and
cholesterol belong to a larger family of chemical compounds called lipids.
All the cholesterol the body needs is made by the liver. It is used to build
cell membranes and brain and nerve tissues. Cholesterol also helps the body
produce steroid hormones needed for body regulation, including processing
food, and bile acids needed for digestion.

People don't need to consume dietary cholesterol because the body can
make enough cholesterol for its needs. But the typical U.S. diet contains
substantial amounts of cholesterol, found in foods such as egg yolks, liver,
meat, some shellfish, and whole- milk dairy products. Only foods of animal
origin contain cholesterol.

Cholesterol is transported in the bloodstream in large molecules of fat
and protein called lipoproteins. Cholesterol carried in low-density
lipoproteins is called LDL-cholesterol; most cholesterol is of this type.
Cholesterol carried in high-density lipoproteins is called HDL-cholesterol.
(See "Fat Words.")

A person's cholesterol "number" refers to the total amount of
cholesterol in the blood. Cholesterol is measured in milligrams per decilitre
(mg/dl) of blood. (A decilitre is a tenth of a litre.)

Doctors recommend that total blood cholesterol be kept below 200 mg/dl.
The average level in adults in this country is 205 to 215 mg/dl. Studies in
the United States and other countries have consistently shown that total
cholesterol levels above 200 to 220 mg/dl are linked with an increased risk
of coronary heart disease. (See "Lowering Cholesterol" in the March
1994 FDA Consumer.)

LDL-cholesterol and HDL-cholesterol act differently in the body. A high
level of LDL-cholesterol in the blood increases the risk of fatty deposits
forming in the arteries, which in turn increases the risk of a heart attack.
Thus, LDL-cholesterol has been dubbed "bad" cholesterol.

On the other hand, an elevated level of HDL-cholesterol seems to have a
protective effect against heart disease. For this reason, HDL-cholesterol is
often called "good" cholesterol.

In 1992, a panel of medical experts convened by the National Institutes
of Health (NIH) recommended that individuals should have their level of
HDL-cholesterol checked along with their total cholesterol.

According to the National Heart, Lung, and Blood Institute (NHLBI), a
component of NIH, a healthy person who is not at high risk for heart disease
and whose total cholesterol level is in the normal range (around 200 mg/dl)
should have an HDL-cholesterol level of more than 35 mg/dl. NHLBI also says
that an LDL- cholesterol level of less than 130 mg/dl is
"desirable" to minimise the risk of heart disease.

Some very recent studies have suggested that LDL-cholesterol is more
likely to cause fatty deposits in the arteries if it has been through a
chemical change known as oxidation. However, these findings are not accepted
by all scientists.

The NIH panel also advised that individuals with high total cholesterol
or other risk factors for coronary heart disease should have their
triglyceride levels checked along with their HDL- cholesterol levels.

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

Here are brief definitions of the key terms important to an
understanding of the role of fat in the diet. Cholesterol: A chemical
compound manufactured in the body. It is used to build cell membranes and
brain and nerve tissues. Cholesterol also helps the body make steroid
hormones and bile acids.

Dietary cholesterol:

Cholesterol found in animal products that are part of the human diet.
Egg yolks, liver, meat, some shellfish, and whole-milk dairy products are all
sources of dietary cholesterol. Fatty acid: A molecule composed mostly of
carbon and hydrogen atoms. Fatty acids are the building blocks of fats.

Fat:

A chemical compound containing one or more fatty acids. Fat is one of
the three main constituents of food (the others are protein and
carbohydrate). It is also the principal form in which energy is stored in the
body.

Hydrogenated fat:

A fat that has been chemically altered by the addition of hydrogen
atoms (see trans fatty acid). Vegetable oil and margarine are hydrogenated
fats. Lipid: A chemical compound characterised by the fact that it is
insoluble in water. Both fat and cholesterol are members of the lipid family.

Lipoprotein:

A chemical compound made of fat and protein. Lipoproteins that have
more fat than protein are called low-density lipoproteins (LDLs).
Lipoproteins that have more protein than fat are called high-density
lipoproteins (HDLs). Lipoproteins are found in the blood, where their main
function is to carry cholesterol.

Monounsaturated fatty acid:

A fatty acid that is missing one pair of hydrogen atoms in the middle
of the molecule. The gap is called an "unsaturation."
Monounsaturated fatty acids are found mostly in plant and sea foods.

Monounsaturated fat:

A fat made of monounsaturated fatty acids. Olive oil and canola oil are
monounsaturated fats. Monounsaturated fats tend to lower levels of
LDL-cholesterol in the blood.

Polyunsaturated fatty acid:

A fatty acid that is missing more than one pair of hydrogen atoms.
Polyunsaturated fatty acids are mostly found in plant and sea foods.

Polyunsaturated fat:

A fat made of polyunsaturated fatty acids. Safflower oil and corn oil
are polyunsaturated fats. Polyunsaturated fats tend to lower levels of both
HDL-cholesterol and LDL-cholesterol in the blood.

Saturated fatty acid:

A fatty acid that has the maximum possible number of hydrogen atoms
attached to every carbon atom. It is said to be "saturated" with
hydrogen atoms. Saturated fatty acids are mostly found in animal products
such as meat and whole milk. Saturated fat: A fat made of saturated fatty
acids. Butter and lard are saturated fats. Saturated fats tend to raise levels
of LDL- cholesterol ("bad" cholesterol) in the blood. Elevated
levels of LDL-cholesterol are associated with heart disease.

Trans fatty acid:

A polyunsaturated fatty acid in which some of the missing hydrogen
atoms have been put back in a chemical process called hydrogenation. Trans
fatty acids are the building blocks of hydrogenated fats.

--E.M.

Government Advice

Dietary guidelines endorsed by the U.S. Department of Agriculture and
the U.S. Department of Health and Human Services advise consumers to:

Reduce total dietary fat intake to 30 percent or less of total
calories.

Reduce saturated fat intake to less than 10 percent of calories.

Reduce cholesterol intake to less than 300 milligrams daily.





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