Fats are a type of nutrient that you get from your diet. It is essential to eat some fats, though it is also harmful to eat too many.
The fats you eat give your body energy that it needs to work properly. During exercise, your body uses calories from carbohydrates you have eaten. But after 20 minutes, exercise then 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, the so-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 give 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 carbohydrates and protein, which each have 4 calories per gram.
All fats are made up of saturated and unsaturated fatty acids. Fats are called saturated or unsaturated depending on how much of each type of fatty acid they contain.
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.
Eating unsaturated fats instead of saturated fats can help lower your LDL cholesterol. Most vegetable oils that are liquid at room temperature have unsaturated fats. There are two kinds of unsaturated fats:
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 some restaurants. They can raise LDL cholesterol levels in your blood. They can also lower your HDL ("good") cholesterol levels.
Trans fats are under review for their health effects. Experts are working to limit the amount of trans fats used in packaged foods and restaurants.
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 the amount of 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 according to a schedule your health care provider gives you.
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Updated by: Michael A. Chen, MD, PhD, Associate Professor of Medicine, Division of Cardiology, Harborview Medical Center, University of Washington Medical School, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.
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