know your fats
american heart association article

Knowing which fats raise LDL cholesterol and which ones don't is the first step in lowering your risk of heart disease. Saturated fat, trans-fatty acids and dietary cholesterol raise blood cholesterol. Monounsaturated fats and polyunsaturated fats don't. Some studies suggest they might even help lower LDL cholesterol slightly when eaten as part of a low-saturated-fat diet.

Saturated fats
Saturated fat is the main dietary cause of high blood cholesterol. The American Heart Association recommends that you limit your saturated fat intake to 7–10 percent of total calories (or less) each day. If you have coronary heart disease or your LDL cholesterol level is 100 mg/dL or greater, your doctor should recommend the Therapeutic Lifestyle Change (TLC) Diet. It recommends 25–35 percent of calories from fat, with less than 7 percent coming from saturated fat. Cholesterol is limited to less than 200 milligrams a day.

Saturated fat is found mostly in foods from animals and some plants.

Foods from animals — These include beef, beef fat, veal, lamb, pork, lard, poultry fat, butter, cream, milk, cheeses and other dairy products made from whole milk. These foods also contain dietary cholesterol.

Foods from plants — These include coconut oil, palm oil and palm kernel oil (often called tropical oils), and cocoa butter.

Hydrogenated fats
During food processing, fats may undergo a chemical process called hydrogenation. This is common in margarine and shortening. These fats also raise blood cholesterol. Use hydrogenated fats only if they contain no more than two grams of saturated fat per tablespoon. The saturated fat content of most margarines and spreads is printed on the package or Nutrition Facts label.

Polyunsaturated and monounsaturated fats — Polyunsaturated and monounsaturated fats are the two unsaturated fats. They're found primarily in oils from plants.

Polyunsaturated fats — These include safflower, sesame and sunflower seeds, corn and soybeans, many nuts and seeds, and their oils.

Monounsaturated fats — These include canola, olive and peanut oils, and avocados.

Both polyunsaturated and monounsaturated fats may help lower your blood cholesterol level when you use them in place of saturated fats in your diet. But a moderate intake of all types of fat is best. Use polyunsaturated or monounsaturated oils — and margarines and spreads made from them — in limited amounts. This is recommended in place of using fats with a high saturated fat content, such as butter, lard or hydrogenated shortenings.

Trans-fatty acids
Unsaturated fatty acids can be in one of two shapes — "cis" and "trans." These terms refer to the physical positioning of hydrogen atoms around the carbon chain. The cis form is more common than the trans form. Trans-fatty acids (TFA) are found in small amounts in various animal products such as beef, pork, lamb and the butterfat in butter and milk. TFA are also formed during the process of hydrogenation, making margarine, shortening, cooking oils and the foods made from them a major source of TFA in the American diet. Partially hydrogenated vegetable oils provide about three-fourths of the TFA in the U.S. diet.

To make foods that will stay fresh on the shelf or to get a solid fat product, such as margarine, food manufacturers hydrogenate polyunsaturated oils. "Hydrogenate" means to add hydrogen. When unsaturated fatty acids are hydrogenated, some of the hydrogen atoms are added on opposite sides of the molecule to the already attached hydrogen. Cis double bonds convert to trans double bonds, and the fatty acids become saturated.

How are trans-fatty acids harmful?
In clinical studies, TFA or hydrogenated fats tend to raise total blood cholesterol levels. Some scientists believe they raise cholesterol levels more than saturated fats. TFA also tend to raise LDL ("bad") cholesterol and lower HDL ("good") cholesterol when used instead of cis fatty acids or natural oils. These changes may increase the risk of heart disease.

Because there are no standard methods, it's difficult to estimate the TFA content of food items. It's also difficult to estimate intake, especially long-term intake. The four most important sources of TFA in one large group of women studied included margarine; beef, pork or lamb as the main dish; cookies (biscuits); and white bread.

Recently the FDA passed a regulation requiring trans fat to be listed on the nutrition label by January 2006. Although changes in labeling are important, they aren't enough. Many fast foods contain high levels of TFA. There are no labeling regulations for fast food, and it can even be advertised as cholesterol-free and cooked in vegetable oil. Eating one doughnut at breakfast (3.2 g of TFA) and a large order of french fries at lunch (6.8 g of TFA) add 10 g of TFA to one's diet, so the lack of regulations for labeling restaurant foods can be harmful to your health.

Is butter better than margarine?
Recent studies on the potential cholesterol-raising effects of TFA have raised public concern about the use of margarine and whether other options, including butter, might be a better choice. Some stick margarines contribute more TFA than unhydrogenated oils or other fats.

Because butter is rich in both saturated fat and cholesterol, it's potentially a highly atherogenic food (a food that causes the arteries to be blocked). Most margarine is made from vegetable fat and provides no dietary cholesterol. The more liquid the margarine, i.e., tub or liquid forms, the less hydrogenated it is and the less TFA it contains.

What can I do to regulate my intake of trans-fatty acids?
The American Heart Association's Nutrition Committee strongly advises that healthy Americans over age 2 limit their intake of saturated fat to 7–10 percent of total calories. Individuals should adjust total fat intake to meet their caloric needs. People who are overweight or obese should limit their total fat intake to no more than 30 percent of total calories.

On the basis of current data, the American Heart Association recommends that consumers follow these tips:

  • Use naturally occurring, unhydrogenated oil such as canola or olive oil when possible.
  • Look for processed foods made with unhydrogenated oil rather than hydrogenated or saturated fat.
  • Use margarine as a substitute for butter, and choose soft margarines (liquid or tub varieties) over harder stick forms. Shop for margarine with no more than 2 grams of saturated fat per tablespoon and with liquid vegetable oil as the first ingredient. Look for those labeled "trans-fat free."
  • French fries, doughnuts, cookies and crackers are examples of foods that are high in TFA. Consume them infrequently.
  • Limit the saturated fat in your diet. If you don't eat a lot of saturated fat, you won't be consuming a lot of TFA.
  • Eat commercially fried foods and commercial baked goods infrequently. Not only are these foods very high in fat, but that fat is also likely to be very hydrogenated, meaning a lot of TFA.
  • Commercial shortening and deep-frying fats will continue to be made by hydrogenation and will contain TFA. That's just one more reason to eat fried fast food infrequently.