Fats &
Cholesterol
- Barbara Struempler, Extension
Nutritionist, Professor, Nutrition and Food Science, Auburn
University.
- Originally prepared by J.
Yvonne Jackson, former Nutrition Specialist.
The controversy over the health risks of
dietary fat and cholesterol has not been resolved. In fact, the issues seem to
be getting more complicated. Heart disease ranks as the leading cause of death
in the United States, and many health professionals consider fats and
cholesterol potential risk factors associated with the cause of heart disease.
Yet, both dietary fats and cholesterol are natural components of the body and
have very important functions for your good health.
Fats
Fats are vital to the normal functioning
of the body. They provide an essential fatty acid, linoleic acid, which
is needed for growth. Fats are the carriers for the fat-soluble vitamins A, D,
E, and K. During digestion, fat must be present so these vitamins can be
absorbed and used in the body.
Fats also are very important energy
sources. They provide 9 calories for each gram of fat. This is at least twice
as many calories as you get from either carbohydrates or proteins.
Much of the flavor of foods is provided
by fats. The body digests fats slowly, and they stay in the stomach longer to
keep you from feeling hungry, providing satiety, or a feeling of fullness.
How Much Fat Do You Need?
The body makes some fatty acids. The ones the body cannot make are called essential
fatty acids and must come from food. Most food fats are triglycerides. A
triglyceride is three acids attached to glycerol, a common chemical compound.
The amount of fat in food varies.
Vegetable oil is 100 percent fat. Butter and margarine are 80 percent fat and
20 percent water and milk solids. Other concentrated fats are lard,
shortening, bacon, and fat back. These fats are easily recognized. The less
visible fats are the ones that tend to cause people to eat too much fat. These
foods include some meats, eggs, milk, cheese, ice cream, nuts, peanut butter,
bakery products, potato chips, and many processed foods.
It has not been determined exactly how
much fat a person should eat. A reasonable level for total fat in the diet for
a healthy person is about 30 percent of the total calories needed.
Saturated And Unsaturated Fats
There are two major types of dietary fat saturated and unsaturated.
Unsaturated fats are further classified as either polyunsaturated or
monounsaturated fats. Together, saturated and unsaturated fats equal total
fat. All foods containing fat contain a mixture of these fats.
Saturated fat raises your blood
cholesterol level more than anything else in your diet. Some of the best ways
to reduce the amount of saturated fat that you eat are to trim meats of fat,
use low-fat dairy products such as milk and cheese, and eat moderate amounts
of meats.
Animal products as a group are a major
source of saturated fat in the average American diet. Butter, cheese, whole
milk, cream, and ice cream all contain high amounts of saturated fat.
Saturated fat is also concentrated in the fat that surrounds meat and in the
white streaks of fat in the muscle of meat (marbling). Poultry, fish, and
shellfish also contain saturated fat, although generally less than meat.
Unsaturated fat actually helps to
lower cholesterol levels when it is substituted for saturated fat. Therefore,
health professionals recommend that you substitute unsaturated fats
(polyunsaturated and monounsaturated fats) for part of any saturated fat
whenever possible.
Polyunsaturated fats are found
primarily in safflower, corn, soybean, cottonseed, sesame, and sunflower oils,
which are common cooking oils. Polyunsaturated fats are also contained in most
salad dressings.
Olive and canola oil (rapeseed oil) are
examples of oils that are high in monounsaturated fats. Like other vegetable
oils, these oils are used in cooking as well as in salads. Recent research
shows that substituting monounsaturated fat (like substituting polyunsaturated
fat) for saturated fat reduces blood cholesterol levels.
The terms saturated and unsaturated
refer to the chemical structure-of the fatty acids. Hydrogenation is a process
of adding hydrogen to change a liquid oil to a more solid form for margarines
and shortenings. Hydrogenation changes polyunsaturated fatty acids into more
saturated fatty acids. The margarines highest in polyunsaturates have liquid
vegetable oil listed as the first ingredient. The next ingredient will be
hydrogenated or partially hydrogenated vegetable oil. If these oils are listed
in reverse, the margarine is not as high in polyunsaturates.
Cholesterol
Cholesterol is essential for forming the
protective covering of nerve cells. It is important to the building of
hormones, and it is a part of the formation of vitamin D.
Cholesterol has received a great deal of
attention since researchers found that the amount of cholesterol in the blood
stream is a good indication of your risk of heart disease. The higher your
blood cholesterol, the higher your risk of having heart disease. Much of the
blood cholesterol is made in the body.
Dietary cholesterol comes only from
animal products; this includes not only the meat of animals but also crab,
shrimp, lobster, and animal products such as milk, egg yolk, butter, and lard.
Plants do not make cholesterol. Therefore, foods made from plants have no
cholesterol unless animal products have been added during processing or
preparation.
Cholesterol and other fat (lipid)
substances are carried in the blood attached to protein. This combination is
called a lipoprotein -- lipid + protein. There are many types of lipoproteins.
High-density lipoproteins (HDL) are the ones responsible for carrying
cholesterol in the blood stream.
The Controversy
There is little dispute over the fact
that your diet influences your levels of blood cholesterol, lipoprotein, and
triglycerides.
- Eating foods with saturated fats
increases your blood level of both cholesterol and triglycerides.
- Eating foods high in cholesterol
increases your blood cholesterol level.
The controversy concerns just how
important this really is. The only relationship between diet and heart disease
that researchers seem to agree on unanimously is that overweight increases
risk of heart disease. There is strong evidence that weight control is the
best protection against heart disease. However, the incidence of heart disease
in the United States is decreasing. And, while the exact reasons are unknown,
contributing factors seem to be that people are eating fewer foods with high
levels of saturated fats and cholesterol and are eating more polyunsaturated
fats. The USDA Dietary Guidelines for Americans suggest that you limit fats,
saturated fat, and cholesterol in your diet and and that you maintain a
healthy weight.
Researchers have now found that the
level of high-density lipoprotein (HDL) in the blood may be a better predictor
of heart disease than blood cholesterol. HDLs remove cholesterol from body
tissues and prevent its buildup. Therefore, the higher your blood level of HDL,
the less risk of your developing heart disease. Factors leading to the
development of HDLs include maintaining normal weight, controlling the fat and
calories in your diet, exercising, not smoking, and reducing alcohol
consumption.
It's important to remember that diet is
only one of the many risk factors associated with cardiovascular diseases.
Others are heredity, your age and sex, smoking, exercise, overweight, blood
pressure, and diseases such as diabetes.
References
Diet and Health: Implications for
Reducing Chronic Disease Risk. 1989. National Research Council, National
Academy Press, Washington, D.C.
Eating to Lower Your High Blood
Cholesterol. 1987. U.S. Department of Health and Human Services, NIH
Publication No. 87-2920, Bethesda, MD 20892.
Ernst, Nancy D., et al. 1988. The National
Cholesterol Education Program: Implications for dietetic practitioners from the
Adult Treatment Panel Recommendations. Journal of the American Dietetic
Association 88:1401-11.
Kris-Etherton, P. M. et al. 1988. The
effect of diet on plasma lipids, lipoproteins and coronary heart disease. Journal
of the American Dietetic Association, 88:1373-1400.
Nutrition and Your Health: Dietary
Guidelines for Americans. 1990. USDA and HEW. Recommended Dietary Allowances.
1989. 10th ed., National Research Council, National Academy Press, Washington,
D.C.
The Surgeon General's Report on Nutrition
and Health. 1988. U.S.Department of Health and Human Services, Public Health
Service, DHHS Publication No. 88-50210, Washington, D.C.
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