Fats are organic compounds that are made up of carbon, hydrogen, and oxygen. They are a source of energy in foods. Fats belong to a group of substances called lipids, and come in liquid or solid form. All fats are combinations of saturated and unsaturated fatty acids.

Fat is one of the three nutrients (along with protein and carbohydrates) that supply calories to the body. Fat provides nine calories per gram, more than twice the number provided by carbohydrates or protein.

Fat is essential for the proper functioning of the body. Fats provide essential fatty acids, which are not made by the body and must be obtained from food. The essential fatty acids are linoleic and linolenic acid. They are important for controlling inflammation, blood clotting, and brain development.

Fat serves as the storage substance for the body's extra calories. It fills the fat cells (adipose tissue) that help insulate the body. Fats are also an important energy source. When the body has used up the calories from carbohydrates, which occurs after the first 20 minutes of exercise, it begins to depend on the calories from fat.

Healthy skin and hair are maintained by fat. Fat helps the body absorb and move the vitamins A, D, E, and K through the bloodstream.

SATURATED FATS

These are the biggest dietary cause of high LDL levels ("bad cholesterol"). When looking at a food label, pay very close attention to the percentage of saturated fat and avoid or limit any foods that are high. Saturated fat should be limited to 10% of calories. Saturated fats are found in animal products such as butter, cheese, whole milk, ice cream, cream, and fatty meats. They are also found in some vegetable oils -- coconut, palm, and palm kernel oils. (Note: Most other vegetable oils contain unsaturated fat and are healthy.)

UNSATURATED FATS

Fats that help to lower blood cholesterol if used in place of saturated fats. However, unsaturated fats have a lot of calories, so you still need to limit them. Most (but not all!) liquid vegetable oils are unsaturated. (The exceptions include coconut, palm, and palm kernel oils.) There are two types of unsaturated fats:

• Monounsaturated fats: Examples include olive and canola oils.
• Polyunsaturated fats: Examples include fish, safflower, sunflower, corn, and soybean oils.

TRANS FATTY ACIDS

These fats form when vegetable oil hardens (a process called hydrogenation) and can raise LDL levels. They can also lower HDL levels ("good cholesterol"). Trans-fatty acids are found in fried foods, commercial baked goods (donuts, cookies, crackers), processed foods, and margarines.

HYDROGENATED AND PARTIALLY HYDROGENATED FATS

This refers to oils that have become hardened (such as hard butter and margarine). Partially hydrogenated means the oils are only partly hardened. Foods made with hydrogenated oils should be avoided because they contain high levels of trans fatty acids, which are linked to heart disease. (Look at the ingredients in the food label.)

Eating too much saturated fat is one of the major risk factors for heart disease. A diet high in saturated fat causes a soft, waxy substance called cholesterol to build up in the arteries. Too much fat also increases the risk of heart disease because of its high calorie content, which increases the chance of becoming obese (another risk factor for heart disease and some types of cancer).

A large intake of polyunsaturated fat may increase the risk for some types of cancer. Reducing daily fat intake is not a guarantee against developing cancer or heart disease, but it does help reduce the risk factors.

• Choose lean, protein-rich foods such as soy, fish, skinless chicken, very lean meat, and fat free or 1% dairy products.
• Eat foods that are naturally low in fat such as whole grains, fruits, and vegetables.
• Get plenty of soluble fiber such as oats, bran, dry peas, beans, cereal, and rice.
• Limit fried foods, processed foods, and commercially prepared baked goods (donuts, cookies, crackers).
• Limit animal products such as egg yolks, cheeses, whole milk, cream, ice cream, and fatty meats (and large portions of meats).
• Look at food labels, especially the level of saturated fat. Avoid or limit foods high in saturated fat.
• Look on food labels for words like "hydrogenated" or "partially hydrogenated" -- these foods are loaded with bad fats and should be avoided.
• Liquid vegetable oil, soft margarine, and trans fatty acid-free margarine are preferable to butter, stick margarine, or shortening.

Children under age 2 should NOT be on a fat-restricted diet because cholesterol and fat are thought to be important nutrients for brain development.

It is important to read the nutrition labels and be aware of the amount of different types of fat contained in food. If you are 20, ask your health care provider about checking your cholesterol levels.

American Heart Association Nutrition Committee; Lichtenstein AH, Appel LJ, Brands M, Carnethon M, Daniels S, et al. Diet and lifestyle recommendations revision 2006: a scientific statement from the American Heart Association Nutrition Committee. Circulation. 2006 Jul 4;114(1):82-96.

Mosca L, Banka CL, Benjamin EJ, Berra K, Bushnell C, Dolor RJ, et al. Evidence-based guidelines for cardiovascular disease prevention in women: 2007 update. Circulation. 2007 Mar 20;115(11):1481-501.