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 byproducts
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
deciliter (mg/dl) of blood. (A
deciliter is a tenth of a liter.)
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 minimize
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
characterized 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. n
--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. n
.
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