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Dietary fats explained

 

What Are Fats

The fats you eat give your body energy that it needs to work properly. During exercise, your body uses up calories, or energy, from carbohydrates after 20 minutes. Then it depends on calories from fat to keep you going.

You also need fat to keep your skin and hair healthy. Fat also helps you absorb vitamins A, D, E, and K. Because these vitamins need fat for your body to be able to use them, they are called fat-soluble vitamins. Fat also fills your fat cells and insulates your body to help keep you warm.

The fats your body gets from your food gives your body essential fatty acids called linoleic and linolenic acid. They are called "essential" because your body cannot make them itself, or work without them. Your body needs them for brain development, controlling inflammation, and blood clotting.

Fat has 9 calories per gram, more than 2 times the number of calories in both carbohydrates and protein, which have 4 calories per gram. That is why foods that are high in fat are called "fattening."

All fats are made up of saturated and unsaturated fatty acids. They are called saturated or unsaturated depending on how much of each type of fat they contain.

Types of Fat

Saturated fats raise your LDL ("bad") cholesterol level. High LDL cholesterol puts you at risk for heart attack, stroke, and other major health problems. You should avoid or limit foods that are high in saturated fats.

  • Keep saturated fats to only 10% of your total daily calories.
  • Foods with a lot of saturated fats are animal products, such as butter, cheese, whole milk, ice cream, cream, and fatty meats.
  • Some vegetable oils -- coconut, palm, and palm kernel oils -- also contain saturated fats. These fats are solid at room temperature.
  • A diet high in saturated fat causes cholesterol to build up in your arteries (blood vessels). Cholesterol is a soft, waxy substance that can cuase clogged, or blocked, arteries.

Eating unsaturated fats instead of saturated fats can help lower your LDL cholesterol. Most vegetable oils that are liquid at room temperature are unsaturated. There are 2 kinds of unsaturated fats:

  • Mono-unsaturated fats, which include olive and canola oil
  • Polyunsaturated fats, which include safflower, sunflower, corn, and soy oil

Trans fatty acids are unhealthy fats that form when vegetable oil hardens in a process called hydrogenation. Hydrogenated fats, or "trans fats," are often used to keep some foods fresh for a long time.

Trans fats are also used for cooking in fast food restaurants. They can raise LDL cholesterol levels in your blood. They can also lower your HDL ("good") cholesterol levels.

  • Trans-fatty acids are found in fried foods, commercial baked goods (donuts, cookies, and crackers), processed foods, and margarines.
  • You should avoid foods made with hydrogenated and partially hydrogenated oils (such as hard butter and margarine). They contain high levels of trans-fatty acids.

It is important to read nutrition labels on foods. This will help you know what kinds of fats, and how much, your food contains.

Talk with your health care provider about how to cut down on how much fat you eat. Your doctor can refer you to a dietitian who can help you learn more about foods and help you plan a healthy diet. Make sure you have your cholesterol levels checked.

References

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.

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.

Krauss RM. Nutrition and cardiovascular disease. In: Libby P, Bonow RO, Mann DL, Zipes DP, eds. Libby: Braunwald's Heart Disease: A Textbook of Cardiovascular Medicine. 8th ed. Saunders;2007:chap 44.


Review Date: 12/13/2008
Reviewed By: Larry A. Weinrauch MD, Assistant Professor of Medicine, Harvard Medical School, Cardiovascular Disease and Clinical Outcomes Research, Watertown, MA. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.
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