Fat is an important component of a diet designed to fuel exercise. While these calories are less accessible to athletes performing quick, intense efforts like sprinting or weight lifting, fat is essential for longer, slower, lower intensity and endurance exercise, such as easy cycling and walking.
Fat provides the main fuel source for long duration, low- to moderate-intensity exercise (think endurance sports such as marathons). Even during high-intensity exercise, where carbohydrate is the main fuel source, fat is needed to help access the stored carbohydrate (glycogen).
Using fat to fuel exercise, however, is dependent upon these important factors:
– Fat is slow to digest and be converted into a usable form of energy.
– After the body break down fat, it needs time to transport it to the working muscles before it can be used as energy.
– Converting stored body fat into energy takes a great deal of oxygen, so exercise intensity must decrease for this process to occur.
Popular low-carbohydrate and high-fat diets, such as the Ketogenic diet and Paleo diet, all work on the premise that lower carbohydrate intake, coupled with high fat and moderate to high protein intake leads to burning body fat as the main fuel source while exercising.
There is, in fact, some scientific evidence that shows long-term low-carb/high-fat diets to be safe and possibly helpful in improving metabolic risk factors for chronic disease. In studies, these diets have shown to be beneficial for performance in ultra-endurance sports while at least several months of adaptation to a low-carb/high-fat diet are required for metabolic changes to occur.