Want to maximize the amount of fat you lose in training? It is often assumed that low-intensity exercise is best for burning fat. During exercise at a very low intensity, fat does account for most of the energy expenditure, while at a moderate intensity fat accounts for roughly 50 percent of energy used. However, at the moderate intensity, the number of calories used per minute is much greater compared to the low intensity, so the total number of calories expended is also greater. The rate of energy expenditure, rather than simply the percentage of energy expenditure derived from fat, is what’s most important. Furthermore, endurance-trained individuals rely less on carbohydrates and more on fat as fuel during submaximal exercise. So, the more running you do, the more fat you will use during subsequent runs.
Now, ignore that preceding paragraph, because to decrease body fat percentage, you don’t necessarily have to use fat during your run. (After all, sprinters have very little body fat and they do little aerobic exercise) Most of the fat used during exercise is in the form of intramuscular triglyceride (fat droplets stored within muscle). Much of the fat from adipose tissue (e.g., around your waistline) is lost during the hours following exercise. The amount of fat loss depends, in part, on the exercise intensity. Following high-intensity exercise, there is a higher rate of fat oxidation than following low-intensity exercise. Because a greater intensity of work can be performed by breaking up the work with periods of rest, interval training is a great way to help decrease body fat percentage.