Dietary Fats: the Good, the Bad and the Ugly

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Fat has gotten a bum rap over the years. Some fats are actually good, and you need them in your diet. Good fats can help you manage your emotions, stay sharp, fight fatigue, and control your weight. But bad fats do exist. They're the ones that can lead to weight gain and raise your risk of heart disease. 

Of the four major types of fats, two are good fats: monounsaturated fats and polyunsaturated fats. They're mostly liquids at room temperature. An example is olive oil. The other two are bad fats: trans fats and saturated fats. They tend to be solid, like butter. 

What You Should Know About Good Fats

Monounsaturated fats come from oils, nuts, seeds, fruits and legumes. They include:

  • Olive oil
  • Canola oil
  • Sunflower oil
  • Peanut oil
  • Sesame oil 
  • Avocados 
  • Peanuts, almonds, macadamia nuts, hazelnuts, cashews and pecans 

This type of fat—in moderation—can help reduce the levels of LDL (low-density lipoprotein), the bad type of cholesterol, in your blood. Monounsaturated fats also are loaded with vitamin E. Vitamin E is an antioxidant that can help protect your cells. 
Polyunsaturated fats also are in oils made from plant sources. But they can also come from seeds, nuts, fatty fish, and soy. Common sources include:

  • Soybean oil
  • Corn oil
  • Safflower oil
  • Walnuts
  • Sunflower, sesame and pumpkin seeds
  • Flaxseed
  • Fatty fish like salmon, tuna, mackerel, herring, trout and sardines
  • Soy milk
  • Tofu 

Polyunsaturated fats also can lower the bad cholesterol in your bloodstream and reduce your risk of heart disease

Two types of polyunsaturated fats are essential to your health: omega-6 and omega-3 fatty acids: 

  • Omega-6s. They can reduce your risk of diabetes and help lower your blood pressure. Good sources of omega-6 fatty acids are seed oils. 
  • Omega-3s. They are good for brain growth and development. They can also help reduce inflammation that leads to heart disease. Main sources of omega-3 fatty acids are fatty fish like salmon and mackerel, as well as flaxseed and walnuts.

What Your Should Know About Bad Fats

Fats that are thought to be harmful include saturated fats that come from animals. They're in meat, butter and cheese, for instance. Saturated fats are also in tropical oils, like coconut, palm and palm kernel. 

The other main type of bad fat is trans fat. These fats are created by a manufacturing process that makes them into solids. You'll find trans fats in snack foods, fried foods, and commercially baked goods like cookies, muffins and doughnuts. Trans fats can increase the bad cholesterol in your blood and lower the good cholesterol (HDL, or high-density lipoprotein). Eating too much trans fat can also make you more prone to type 2 diabetes

Do the Math on Fats 

All fats, whether good or bad, have the same number of calories: 9 per gram of the food they're in. Fats are dense, so small amounts can add lots of calories to your diet. For good health, adults should limit total fat intake to between 20% and 35% of their daily calories.

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Medical Reviewer: William C. Lloyd III, MD, FACS
Last Review Date: 2020 Sep 10
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  2. Healthy Eating Pyramid. Harvard T.H. Chan School of Public Health.

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  4. Nutrition. Centers for Disease Control and Prevention.