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You are here : 3-RX.com > Medical Encyclopedia > Diet and Nutrition > Dietary Fat
      Category : Health Centers > Food, Nutrition, and Metabolism

Dietary Fat

Alternate Names : Fat, Fatty Acids

Overview & Description | Functions and Sources

Dietary fat is the fat that is found in food. Fat is one of four substances in food that provide calories. The other three are carbohydrate, protein, and alcohol. There are three types of natural fats found in foods. These are monounsaturated, polyunsaturated, and saturated fats. Most foods contain all three fats in different amounts.

The body can use all three types of fat. Dietary fat has very important functions in the body. Only a moderate amount of fat is needed for good health. Too much fat or the wrong type of fat can be harmful. A healthy diet should have more unsaturated fat than saturated fat.

Fat is the most concentrated source of calories. It provides 9 calories per gram. Carbohydrate and protein provide 4 calories per gram. Alcohol provides 7 calories per gram. So any type of fat should be used sparingly in the diet.


Fats and oils are made up of basic units called fatty acids. Each type of fat or oil is a mixture of different fatty acids. Most of the fat in a person's diet should come primarily from fats that contain mostly unsaturated fatty acids. These foods can be from both plant and animal sources. They are usually liquid at room temperature. Unsaturated fatty acids include monounsaturated and polyunsaturated fatty acids.

  • Fats that are mostly monounsaturated are canola, olive, and peanut oils.
  • Fats that are mostly polyunsaturated are safflower, corn, and sunflower oils, soybeans, many nuts and seeds, and seafood.
  • Replacing saturated fats with unsaturated fats in the diet has been shown to help lower blood cholesterol levels. NHLBI recommends that up to 20% of total daily calories should be monounsaturated fat. Up to 10% of total daily calories should be polyunsaturated fat. The American Heart Association recommends up to 10% of total daily calories from polyunsaturated fats and up to 15% from monounsaturated fats.

    An important polyunsaturated fat is omega-3 fatty acid, which comes mostly from fish sources. Omega-3 is an essential fat, which means that the body can't make it. It must be derived from foods. Some studies suggest that omega-3 may help lower the risk for heart disease and heart attacks.

    Saturated fats are considered bad fats. They come mostly from animal foods and are usually solid at room temperature. The only plant sources of saturated fats are oils made from coconut and palm. Saturated fat in the diet should be limited to no more than 8% to 10% of total calories.

    Eating a lot of saturated fat may raise the carriers of bad cholesterol in the blood. These bad carriers are called low-density lipoproteins, or LDL. A high amount of LDL in the blood can lead to plaque buildup in the arteries. This can cause atherosclerosis. Having high cholesterol levels in the blood is a major risk factor for heart disease.

    Another type of fat is trans fats. These fats are formed when vegetable oils are processed into margarine or shortening through a process called hydrogenation. Sources of trans fats in the diet include snack foods and baked goods made with partially hydrogenated vegetable oil or vegetable shortening. Trans fatty acids also occur naturally in some animal products such as dairy products. Trans fats raise LDL cholesterol levels and may also lower HDL cholesterol in the blood. They also raise total blood cholesterol levels but not as much as more saturated fatty acids. It's not clear if trans fats that occur naturally have the same effect on cholesterol and heart disease as those produced by hydrogenation of vegetable oils.

    To limit the amount of trans fats in the diet, the American Heart Association (AHA) recommends using a margarine with liquid vegetable oil as the first ingredient and no more than 2 grams of saturated fat per tablespoon. Daily intake of fats and oils should be limited to no more than 5 to 8 teaspoons.

    Fats are shown at the very top of the food guide pyramid. This means that these foods should be used sparingly for a healthy diet. But following a diet that is extremely low in fat can cause vitamin and mineral deficiencies. However, most people would find it very difficult to limit their fat intake severely enough to cause these deficiencies. It is important to include some fat in the daily diet.

    Reading food labels is a good way to identify foods that are high in fat. All food labels are required to list the grams of total fat and saturated fat. A food with 3 grams or less of fat per serving is considered a low-fat food. Be aware that just because a food is fat free doesn't mean it's calorie free! Many foods that are low in fat contain high levels of sugar and calories per serving.

    Tips for lowering fat intake include:

  • adding fish to the diet
  • choosing low-fat or skim dairy products
  • eating leaner cuts of meat
  • eating a meatless meal at least once a week
  • removing skin from poultry before eating
  • trimming off visible fat before cooking meat


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    Dietary Fat: Functions and Sources

    Author: Susan Harrow Rago, RD, MS
    Reviewer: Melissa Sanders, PharmD
    Date Reviewed: 06/11/01

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