Fat Intake & Utilization for Exercise

Fat Utilization for Exercise

Along with carbohydrates, fat is a vital energy source, even when the body is at rest.  As intensity changes during the course of the exercise, so does the body’s preferred energy source. Since these shifts continue throughout the activity, stores of both carbs and fat need to be properly maintained for the most efficient performance. 

Fatty acids are the basic building blocks of fats. The most significant portion of fat in the diet comes in the form of triglycerides, three fatty acids attached to a glycerol molecule. Fatty acids (made from molecules of carbon, hydrogen, and oxygen) combine to form “chains” of various lengths. Some chains are saturated with hydrogen and others remain unsaturated. Unsaturated fats can be further separated into “mono” or “ poly” designations depending on their structure; both mono and polyunsaturated fats are considered “heart-healthy.” Many sources of dietary fat are made up of combinations of both saturated and unsaturated fats.

Like the “essential” amino acids, essential fatty acids must be obtained from the diet.  Two of the most important types of essential polyunsaturated fats are omega-3 (alpha-linolenic acid) and omega-6 (linoleic acid).

Functions of Fat

Proper fat intake ensures adequate energy reserves, allows for the absorption of fat-soluble vitamins (vitamin A, D E and K), facilitates nerve conduction, and helps to regulate body temperature.  Omega-3 fats are important for brain function, immunity as well as skin, eye and heart health. Omega-6 fats also play a role in brain function and contribute to growth and development.

Fat breakdown, absorption, and transport are more complicated than carbohydrate and protein because fat does not dissolve in water (and the body is mostly water). Since additional steps are required, digestion of high-fat meals and snacks can take several hours. Athletes need to keep this in mind when making meal choices surrounding workout times.

In muscle tissue, digested fat it is used immediately for energy or stored for later use in the muscle and adipose tissue.

Exercise intensity can be expressed as a measure of oxygen consumption (VO2 max). As exercise intensity changes, so do the body’s preferred energy source (see Table 5.1). During a lower intensity activity (25% VO2 max), the majority of energy comes from fat. At 85% VO2 max, mostly stored carbohydrates are utilized. When intensity is more moderate (approximately 65% VO2 max) carbs and fat contribute equally. Since exercise intensity changes dramatically throughout an activity, these energy systems are constantly shifting. When dietary intake is inadequate these systems (and performance) can be compromised.

Estimated Fat and Carbohydrate Utilization During Exercise

  • Exercise at 25% VO2 max
    • 20% or less from carbohydrate and 80% from fat
  • Exercise at 65% VO2 max
    • Fats & carbohydrate contribution is approximately equally
  • Exercise at > 85% VO2 max
    • Energy contribution from fats diminishes to  < 25%
    • Muscle glycogen becomes the preferred energy source

Fat in the Athlete’s Diet

Healthy options for fats include plant-based oils like olive, canola and sunflower, nuts, and seeds; peanut butter, cheese, fatty fish like salmon and tuna are also tasty, nutrient dense choices.   

Protein sources like low fat or full-fat dairy, egg yolks, and meat also contain some fat, and much of this fat is saturated. Since these foods offer many other healthy nutrients like protein and calcium, for example, it’s recommended to incorporate them into a healthy diet. Most saturated fats are solid at room temperature and come from animal products; some exceptions would be palm oil and coconut oil.

Sources of omega-3 fats include leafy greens vegetables, flaxseed, canola, soy, walnuts, and cold water seafood, like salmon. Omega-6 fats can be found in vegetable oils including corn, soy, peanut, and sunflower oil; many of these can be found in margarine spreads and salad dressings.

When and How Much

It is recommended that fat intake range from 20 to 35% of total calories; less than 20% does not benefit performance and could be detrimental to health. Diets that are too high in fat can lead to undesired weight gain and are not recommended for athletes. Ten-percent or less should come from saturated sources. Endurance and strength athletes will need to adjust their fat intake accordingly depending on their carbohydrate and protein needs.

Since fat takes longer to digest, athletes should moderate their fat intake prior to activity to avoid an upset stomach. Athletes are encouraged to incorporate the majority of their fat into pre-workout meals when they have 3 to 4 hours before being active. Post workout fat intake can be more flexible as long as it doesn’t interfere with carbohydrates and protein needs.


  • Fat is a highly efficient energy source used almost exclusively at various levels of exercise
  • Building blocks of fats are fatty acids
  • Sources include nuts, seeds, peanut butter, dairy, fish, egg yolks and visible fat on meats
  • Fat intake should be 20 to 35% of total calorie intake with 10% or less coming from saturated fats

Learn more about nutrition and nutrition for athletes in the Fitness Nutrition Coach program, the Sports Nutrition Specialist program, or the Certified Personal Fitness Chef program.