Your Guide to Fats
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
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
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
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
such as vegetable shortening and margarine, are solid at room
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,
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
(See "Lowering Cholesterol" in the March 1994 FDA
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"
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
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
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
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
"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
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
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.
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
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
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
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.