The simple (and complex) answer is that there is no “best way” to lose fat. Each client will respond differently to a training program. However, there are some principles fitness professionals can apply when designing their clients’ programs.
Activities that incorporate many muscle groups and are weight bearing use more calories per minute and are therefore better suited for fat loss than non-weight-bearing activities that do not use many muscles.
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 only about 50 percent of the energy used. However, since the number of calories used per minute is much greater at a moderate to high intensity than at a low intensity, the total number of calories expended during a moderate- to high-intensity workout is greater than it is during a low-intensity workout of the same duration; consequently, the total number of fat calories expended is also greater during the higher-intensity workout. The rate of energy expenditure, rather than simply the percentage of energy expenditure derived from fat, is important in determining the exercise intensity that will use the most fat. Furthermore, endurance-trained individuals rely less on carbohydrates and more on fat as a fuel source during submaximal exercise (Kiens 1997). Thus, the more aerobically trained your clients become, the more fat they will use during subsequent exercise sessions.
To decrease body fat percentage, your clients do not necessarily have to use fat during exercise. Much of the fat from adipose tissue (as opposed to intramuscular fat, which is primarily used during exercise) is lost in the hours following exercise. Moreover, the amount of fat lost after a workout depends, in part, on the exercise intensity during the workout. Following high-intensity exercise, the rate of fat oxidation is higher than it is following low-intensity exercise (Mulla et al. 2000; Phelain et al. 1997). Because clients can perform a greater intensity of work if the work is broken up with periods of rest, interval training is a great way to perform high-intensity work and help decrease body fat percentage.
Both strength training and endurance exercise have been shown to decrease body fat percentage. However, aerobic exercise appears to have a greater impact on fat loss than does strength training (Ballor et al. 1996; Dolezal & Potteiger 1998; LeMura et al. 2000). A combination of endurance and strength training results in more fat loss than either exercise regimen alone (Dolezal & Potteiger 1998), possibly because clients who perform both activities spend more time exercising.