Throughout the 1980s and ’90s, dietary trends led to the promotion of low-fat, higher carbohydrate diets as the healthiest way to eat. But statistics later revealed that as Americans adopted these lower fat diets, rates of overweight and obesity climbed. The number of people with diabetes, a condition directly related to being overweight or obese, also grew.

As a result, the trend shifted away from limiting all dietary fats and moved toward understanding the different types of fat in the diet, and choosing healthier fats, which may prevent or delay the development of some diseases.

The Different Types of Dietary Fat

There are four different categories of dietary fat: monounsaturated, polyunsaturated, saturated, and trans. These fats differ in their chemical structures and physical states—and how your body responds to them.

Mono and polyunsaturated fats are generally liquid at room temperature. Monounsaturated fats are found in vegetable oils like canola, olive, and sunflower oils; non-oil sources include avocados and nuts. Polyunsaturated fats include omega-3 and omega-6 fatty acids. Omega-3s are found in oily fish such as salmon and anchovies as well as some plant foods, including flaxseeds and walnuts. Omega-6 fatty acids are found in vegetable oils like soybean, corn, and safflower oils.

Saturated and trans fats are usually solid at room temperature. They include animal fats such as lard and butter, the visible fat seen on cuts of meat and poultry, coconut and palm oils, cocoa butter, and the fats found in whole-milk dairy products. Trans fats are formed when liquid fats are processed and hardened into solids; these are considered the most dangerous fats of all.

Monounsaturated, polyunsaturated, saturated, and trans fats play different roles in various body processes, including the transport of cholesterol in the bloodstream, and the development or prevention of inflammation.

Why Bad Fats Are Bad

Generally, saturated and trans fats are considered unhealthy because they tend to raise blood cholesterol levels, which can contribute to atherosclerosis, or plaque formation in the arteries (vessels that carry blood to the heart and throughout the body). Plaque buildup in the arteries increases your risk of heart disease, heart attacks, and strokes. Some saturated fats, such as those found in coconut oil, can actually increase HDL (“good”) cholesterol, but may still contribute to heart disease in ways unrelated to their effect on cholesterol.

Why Good Fats Are Good

Replacing saturated fats in the diet with unsaturated fats can help reduce the risk of developing chronic diseases such as diabetes, heart disease, and possibly some forms of cancer. Some unsaturated fats may also help alleviate symptoms of inflammatory diseases such as arthritis. Studies have consistently shown that substituting polyunsaturated fats for saturated fats can reduce total and LDL (low-density lipoprotein, or “bad”) cholesterol levels in the blood. At the same time, monounsaturated fats raise beneficial HDL (high-density lipoprotein) cholesterol levels. Some unsaturated fats, especially omega-3 fats, are known to have anti-inflammatory properties.

6 Tips for Incorporating Healthy Fats into Your Diet

You need fat in your diet; it acts as insulation for your body, and is essential for hormone production, nutrient transport and absorption, and new cell growth. Fat also plays an important role in how satisfied you feel after eating.

To reduce your risk of developing symptoms and diseases associated with unhealthy fats, follow this advice from Alison Massey, MS, RD, LDN, CDE, registered dietitian with the Center for Endocrinology at Mercy Medical Center:

    1. Replace some or all of the meat in your diet with other sources of protein, such as fish, nuts, and legumes.

    2. If you eat meat, choose the leanest cuts and grinds.

    3. If you eat dairy products, choose reduced-fat, low-fat and fat-free varieties.

    4. Replace solid fats used in cooking and baking with liquid oils. (For baked goods, look for recipes that replace some or all of the butter with vegetable oil.)

    5. Read the Nutrition Facts label on processed food products; look for those that are low in fat and contain 0 grams of trans fats.

    6. Eat a diet full of fiber from fresh fruits and vegetables. In addition to the nutritional benefits gained from eating a diet rich in plant foods, the fiber in these foods helps carry excess fat out of your body before it can be absorbed into your bloodstream.

Alison Massey, MS, RD, LDN, CDE, reviewed this article. 


"Know Your Fats." American Heart Association. Updated May 9, 2014.  

Willet, W. "Dietary Fats and Coronary Artery Disease." Journal of Internal Medicine 272, 1 (2012): 13-24. 

Willett, WC, and RL Leibel. "Dietary Fat Is Not a Major Determinant of Body Fat." American Journal of Medicine Dec 30; 113 Suppl 9B (2002): 47S-59S.

"Polyunsaturated Fats and Monounsaturated Fats." Centers for Disease Control and Prevention. Last reviewed Sept. 27, 2012. 

"What Is Atherosclerosis?" National Heart, Lung, and Blood Institute. Page reviewed July 1, 2011.