Since March is National Nutrition Month, I am writing about the major nutrients in our diets: carbohydrates, fats and protein. Last week I provided information about carbohydrates, the major energy source in our diets. This week I will write about fats, including saturated fats, unsaturated (monounsaturated, polyunsaturated and trans) fats, omega-3 fats and cholesterol.

Fats tend to get a bad reputation since they are higher in calories than carbohydrates and protein and are associated with obesity and heart disease when eaten in excess. While this is true and some dietary fats are detrimental to your health, others have health benefits. These benefits are linked to the effect of the fats on the LDL (“bad”) and HDL (“good”) cholesterol in your blood.

Cholesterol is only found in animals and is associated with an increased risk of heart disease. Saturated fats are primarily consumed in animals as well as tropical oils such as palm and coconut oil and tend to raise LDL (“bad”) cholesterol. In fact, saturated fat is more strongly linked to heart disease than is cholesterol.

Unsaturated fats are found in plant oils. Polyunsaturated fats tend to lower both LDL and HDL cholesterol. Monounsaturated fats are associated with lower LDL, but they do not lower HDL cholesterol – this is better. Oils high in polyunsaturated fats include corn and soybean oil while olive and canola oils are rich in monounsaturated fats.

Trans fats are found mostly in modified oils which are hydrogenated to make them more solid and have a longer shelf life. For example, when corn oil (unsaturated fat) is partially hydrogenated it becomes more trans and is more solid – margarine. Trans fats are used in baked and fried foods and can be identified on food labels (most of the time) or by the words “hydrogenated” or “partially hydrogenated” in the ingredient list. Trans fats have the effect of raising LDL while lowering HDL cholesterol, a bad combination!

There are three essential omega-3 fats come in the diet: ALA, EPA and DHA. Two of these, EPA and DHA, are primarily found in fish and are associated with reduced risk of heart attack due to their beneficial effects reducing inflammation and blood clotting. Other sources of omega-3 fats include flax seeds, which are high in ALA. The evidence in strongest for beneficial health effects of EPA and DHA, so eating fish or taking fish oil supplements is recommended for many people.

According to current recommendations, dietary fat should account for 20 to 35 percent of your total calories. The typical American diet is too high in total fat, largely from unhealthy sources. Your goal should be to reduce the amount of fat you eat and to make food choices that will shift your intake of fat away from unhealthy sources (cholesterol, saturated and trans fats) to more healthy sources (monounsaturated and omega-3 fats). Don’t forget that all fat contains calories, so don’t overeat even the healthier fats!

You can reduce your saturated fat and cholesterol intake by eating less meat or eating leaner beef or poultry and consuming fat-free dairy products. Avoid trans fats by staying away from fried foods and checking the labels on prepackaged snacks. Fortunately, trans fats are less common now than they were even a few years ago. Switch to olive or canola oil to increase your consumption of monounsaturated fats and eat fish two to three times per week (or take a supplement) to get enough omega-3 fats. Some of the health benefits of the Mediterranean diet are thought to be due to the higher consumption of olive oil and fish that is typical in that region.

Brian Parr, Ph.D., is an associate professor in the Department of Exercise and Sports Science at USC Aiken where he teaches courses in exercise physiology, nutrition and health behavior.