If a group of athletes was asked what they would most like to change about themselves to improve performance, chances are one of the most popular answers would involve losing body fat or improving body composition. However, a common misperception of athletes is that leaner or leanest is always best. All athletes are genetically different in terms of body types and body composition. There is not a single equation for body composition. Altering body composition is dependent on energy and calorie intake. Athletes must train when in energy- or calorie-restricted state to tap into body fat stores and change body composition. For some athletes, severe calorie restriction is required to reach and maintain lean body composition. This type of restriction will negatively affect performance. Athletes must be wise about making attempts to alter body composition. Body composition should be a focus during off-season training when peak performance is not required. Athletes are motivated to alter or improve body composition for a number of reasons. It is a simple thought, but a decrease in body fat essentially means that an athlete will be running, jumping, swimming, and changing direction with less mass or weight to move. For example, a male athlete who weighs 75 kg and has 10% body fat carries 7.5 kg of adipose tissue or body fat. If the athlete reduces his body fat to 7%, he has lowered his fat mass to approximately 5.2 kg; his body can move more efficiently with less body fat. Athletes whose movement is more efficient or economical will accomplish the same objective with less energy.

A leaner athlete moving with less body fat will be more efficient and expend less energy doing the same task as someone who is carrying more body fat. In addition, athletes such as high jumpers or sprinters want to maximize strength: mass ratios in order to optimize their performance. Maintenance of strength and power is key while minimizing body weight or mass. If strength is lost along with mass, improvements in performance will not be realized.

The desire for athletes to be leaner, along with a need for many nonathletes to lose weight, has created an explosion of fat-burning and weight-loss supplements. These supplements are one of the most popular types of products on the market. A recent search of a popular online sports supplement store found nearly 200 names and brands of so-called fat burners available for purchase. Unfortunately, fat burners and weight-loss supplements are also some of the most dangerous: They often contain potent stimulants much more powerful than caffeine that can affect the cardiovascular function and result in death. Extreme caution should be used when choosing these products. Another concern is that these supplements are often adulterated and tainted with ingredients or pharmaceutical drugs not listed on labels that may have powerful (often harmful) effects on the body.

Most fat burners and weight-loss supplements can be assigned to one of three categories:

  • Stimulant based: These contain stimulants such as caffeine, epinephrine, synephrine, guarana, and many others. Product claims include the ability to speed up resting metabolic rate and burn fat.
  • Appetite suppressants: Assist in controlling appetite and limiting calorie intake.
  • Fat malabsorptive: These ingredients limit the amount of fat absorbed during digestion, resulting in lowered calorie intake. Chitosan, which is a structural element found in the shell of crabs, shrimp, and lobster, is a popular ingredient found in weight-loss supplements due to its speculated ability to bind fat and prevent its absorption. These types of products can have some undesirable side effects such as loose stools and diarrhea. In addition, their use will also limit the absorption of fat-soluble vitamins, healthy fats, and essential fatty acids need for optimal function.