Knowing which fats raise LDL cholesterol and which ones don't is the first step in lowering your risk of heart disease. In addition to the LDL produced naturally by your body, saturated fat, trans-fatty acids and dietary cholesterol can also raise blood cholesterol. Monounsaturated fats and polyunsaturated fats appear to not raise LDL cholesterol; some studies suggest they might even help lower LDL cholesterol slightly when eaten as part of a low-saturated and trans-fat diet.
The American Heart Association's Nutrition Committee strongly advises these fat guidelines for healthy Americans over age 2:
- Limit total fat intake to less than 25–35 percent of your total calories each day;
- Limit saturated fat intake to less than 7 percent of total daily calories;
- Limit trans fat intake to less than 1 percent of total daily calories;
- The remaining fat should come from sources of monounsaturated and polyunsaturated fats such as nuts, seeds, fish and vegetable oils; and
- Limit cholesterol intake to less than 300 mg per day, for most people. If you have coronary heart disease or your LDL cholesterol level is 100 mg/dL or greater, limit your cholesterol intake to less than 200 milligrams a day.
For example, a sedentary female who is 31–50 years old needs about 2,000 calories each day. Therefore, she should consume less than 16 g saturated fat, less than 2 g trans fat and between 50 and 70 grams of total fat each day (with most fats coming from sources of polyunsaturated and monounsaturated fats, such as fish, nuts, seeds and vegetable oils).
Saturated fat
Saturated fat is the main dietary cause of high blood cholesterol. Saturated fat is found mostly in foods from animals and some plants. Foods from animals include beef, beef fat, veal, lamb, pork, lard, poultry fat, butter, cream, milk, cheeses and other dairy products made from whole and 2 percent milk. All of these foods also contain dietary cholesterol. Foods from plants that contain saturated fat include coconut, coconut oil, palm oil and palm kernel oil (often called tropical oils), and cocoa butter.
Back to top of page
Hydrogenated fat
During food processing, fats may undergo a chemical process called hydrogenation. This is common in margarine and shortening. These fats also raise blood cholesterol. The saturated fat content of margarines and spreads is printed on the package or Nutrition Facts label.
Back to top of page
Polyunsaturated and monounsaturated fats
Polyunsaturated and monounsaturated fats are the two unsaturated fats. They're found mainly in many fish, nuts, seeds and oils from plants. Some examples of foods that contain these fats include salmon, trout, herring, avocados, olives, walnuts and liquid vegetable oils such as soybean, corn, safflower, canola, olive and sunflower.
Both polyunsaturated and monounsaturated fats may help lower your blood cholesterol level when you use them in place of saturated and trans fats. But a moderate intake of all types of fat is best. Keep total fat intake between 25 and 35 percent of calories, with most fats coming from sources of polyunsaturated and monounsaturated fatty acids such as fish, nuts and vegetable oils.
Back to top of page
Trans-fatty Acids and Hydrogenated Fats
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. The trans fat content of foods is printed on the package of the Nutrition Facts label. Keep trans fat intake to less than 1 percent of total calories. For example, if you need 2,000 calories a day, you should consume less than 2 grams of trans fat.
Trans-fatty acids are also formed during the process of hydrogenation. "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.
Back to top of page
How are trans-fatty acids harmful?
In clinical studies, TFA or hydrogenated fats tended 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.
As of January 2006, the FDA requires trans fat to be listed on the nutrition label. 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 grams of TFA to one's diet, so the lack of regulations for labeling restaurant foods can be harmful to your health.
Back to top of page
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.
Back to top of page
Regulating your intake of trans-fatty acids
The American Heart Association's Nutrition Committee strongly advises that healthy Americans over age 2 limit their intake of trans fat to less than 1 percent of total calories.
Based on current data, the American Heart Association recommends that consumers follow these tips:
- Choose a diet rich in fruits, vegetables, whole-grain, high-fiber foods, and fat-free and low-fat dairy most often.
- Keep total fat intake between 25 and 35 percent of calories, with most fats coming from sources of monounsaturated and polyunsaturated fats such as fish, nuts, seeds and vegetable oils most often.
- Use naturally occurring, unhydrogenated vegetable oils such as canola, safflower, sunflower or olive oil most often.
- Look for processed foods made with unhydrogenated oil rather than partially hydrogenated or hydrogenated vegetable oils or saturated fat.
- Use soft margarine as a substitute for butter, and choose soft margarines (liquid or tub varieties) over harder stick forms. Look for ”0 g trans fat” on the Nutrition Facts label.
- French fries, doughnuts, cookies, crackers, muffins, pies and cakes are examples of foods that are high in trans fat. Don't eat them often.
- 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 trans fat.
- Limit commercially fried foods and baked goods made with shortening or partially hydrogenated vegetable oils. Not only are these foods very high in fat, but that fat is also likely to be very hydrogenated, meaning a lot of trans fat.
- Limited fried fast food. Commercial shortening and deep-frying fats will continue to be made by hydrogenation and will contain saturated fat and trans fat.
