Athlete Conditioning and Metabolizing Fat

Improving athletic endurance through a program of endurance training increases both the size and number of mitochondria (and related oxidative enzymes) inside cells, which increases the capacity of the athlete to use a greater amount of fat during physical activity. Since athletes store far more fat calories than carbohydrate calories, increasing the ability to use fat induces a proportionate reduction of carbohydrate reliance, thereby increasing endurance. Put simply, if you can burn more fat at higher exercise intensities, you can make your carbohydrate stores last longer so that your endurance is improved. It is important to note, however, that fat oxidation cannot be improved to the point of eliminating the need for carbohydrate (muscle glycogen) during intense exercise. Also, a greater ability to metabolize fat for energy should not motivate an athlete to increase the proportionate intake of fat. Assuming an adequate caloric intake, athletes can manufacture and store the fat they need, and higher intakes of dietary fat are a clear risk factor in atherosclerotic heart disease. Even a short-term increase in fat intake with a concomitant decrease in carbohydrate intake for only 3 to 5 days leads to a reduction in endurance performance when compared with a high carbohydrate intake.