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 ALL ABOUT FATS AND 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 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.

 

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