Fat is not a four-letter word, although many still consider it a dirty word when it comes to nutrition, fitness and exercise. Those who lived through the ‘90s undoubtedly remember when the food industry marketed everything as “low-fat” in the guise that it was a healthier option. While it’s true that having high levels of body fat can be a risk factor for many types of chronic diseases, dietary fat—specifically, the right kinds of fat—is an essential component of a healthy diet.

Here are 10 things to know about fat as it relates to helping create the energy your body needs for your favorite physical activities.

1. The terms "fat" and "lipids" are used interchangeably when discussing how the body metabolizes energy. Lipids include triglycerides, which are formed by combining a glycerol with three fatty acids, fatty acids and cholesterol. The majority of lipids in food and the body are in the form of triglycerides.

2. In the human body, fat can be stored in skeletal muscle, the liver and adipose tissue, and is used for many functions. This includes providing structure for cell membranes, insulating and protecting vital organs, regulating endocrine system function (how hormones are produced), helping transport vitamins and minerals around the body, and as a source of energy for many cellular functions. Fat provides approximately 70% of the energy for bodily functions when at rest and during low-intensity physical activity.

3. Fat contains carbon, hydrogen and oxygen atoms. Because fatty-acid chains have more carbon and hydrogen relative to oxygen, they yield more energy per gram. Fats provide 9 calories of energy per gram while proteins and carbohydrates each produce 4 calories per gram.

4. There are different types of fat: saturated, monounsaturated and polyunsaturated. Saturated fatty acids contain hydrogen on the carbon bonds. Because the body can produce these fats on its own, there are no dietary requirements for the consumption of saturated fats. Unsaturated fats contain double carbon bonds with fewer hydrogen molecules. Fatty acids with one double carbon bond are called monounsaturated, while fatty acids with two or more carbon bonds are polyunsaturated.

5. Saturated fats tend to be solid when at room temperature and can be found in animal, dairy and packaged food products in addition to coconut and palm kernel oils. A diet high in saturated fats could be a risk factor for heart disease.

6. Unsaturated fats are liquid at room temperature. Polyunsaturated fats include the essential (meaning they must be consumed in the diet) omega-3 fatty acids found in many types of cold water fish and omega-6 fatty acids, which are found in soybean, corn and safflower oils (and foods made with those oils). Monounsaturated fats are found in olive, peanut and canola oils. Other foods that contain poly- and monounsaturated fats include avocados, flax and chia seeds, and almonds.

7. Lipolysis is the breakdown of triglycerides into a glycerol and three fatty acids for the purpose of producing adenosine triphosphate (ATP), which is the chemical that fuels muscle activity. When the body needs energy for physical activity, the sympathetic hormone norepinephrine acts with receptor cells in adipose tissue to release the enzyme lipoprotein lipase, which breaks up triglycerides into the free fatty acids used by the mitochondria during a process called beta oxidation. The result is that the three fatty acids and one glycerol of a single triglyceride can produce 457 molecules of ATP. By comparison, glycolysis (the conversion of glycogen to ATP) yields 36 ATP molecules per one unit of glucose. Lipolysis is a slower process, which explains why it is the dominant source of energy during periods of rest or low-intensity physical activities. Glycolysis creates ATP more quickly, which makes it the “go-to” choice for ATP during moderate- to high-intensity physical activities. High-intensity interval training can burn more calories, while low- to moderate-intensity steady-state exercise can help improve aerobic capacity.

8. The myth of the fat-burning zone is not really a myth—lipolysis requires oxygen, which is readily available during lower-intensity physical activities. Muscles use primarily fat as the source of ATP during low-intensity activity; however, as the intensity of exercise increases, the demand for energy is greater and the working muscles will need ATP more quickly than lipolysis can provide. While muscles relying on lipolysis for energy are using fat, the overall energy consumption is relatively low. In other words, working at an intensity at which lipolysis is the primary source of ATP will not burn that many total calories.

9. Stress can increase body fat. During periods of stress, or in reaction to certain drinks that elevate the sympathetic hormones of cortisol and norepinephrine, the body releases more triglycerides into the blood stream to be used for energy for the working muscles. However, if there is no significant physical activity to use that energy, those triglycerides will be returned to the adipose tissue for storage until they are needed.

10. Trans fat is made when an unsaturated fat, which is normally liquid at room temperature, is hydrogenated (adding hydrogens) so that it turns into a solid. This manufacturing process increases the shelf life of a food product, which is why many packaged foods can be high in trans fats. However, because it changes the chemical structure of fat, trans fats have been linked to heart disease and elevated levels of low-density lipoprotein (LDL) cholesterol.

The food consumed in the daily diet should provide adequate levels of protein, which is used to repair damaged muscle fibers and produce new tissues, and carbohydrate and fat, which fuel cellular functions. One of the most important functions of fat in the diet is to provide a source of energy for a number of bodily functions, including muscle contractions for physical activity. Don’t think of fat as something bad that should be avoided; rather, think of it as an important source of energy for the body.

A healthy diet should contain adequate amounts of mono- and polyunsaturated fats, with only limited amounts of saturated and trans fats. Let’s all agree to leave the “low-fat” nonsense in the past where it belongs, and appreciate the role of fat that it plays in supporting our favorite types of exercise.

Learn more about Nutrition for Sports, Exercise and Weight Management.