Losing fat and developing a more shapely physique may not as simple as shedding pounds. Depending on your dieting methods, you can lower your reading on the bathroom scale by shedding fat mass or lean muscle mass, a process called catabolic weight loss, which will really only hinder your weight loss goals in the long run.
Anabolism, a process in which the body uses simple molecules to create complex ones, allows the body to construct and maintain muscle cells and tissues. Catabolism, by contrast, is the process in which the body breaks down these complex molecules into smaller ones.
Although severe calorie restriction may induce rapid weight loss initially, it's not effective in the long term as it may in fact lead to catabolic weight loss, the effects of which may eventually hamper your body's ability to burn fat. The ideal approach, by contrast, is to moderately reduce your calorie intake and perform regular exercise, a combination of which will increase lean muscle mass and burn fat.
Muscle is a metabolically active tissue, meaning that it requires a constant supply of energy. According to experts at the U.S. Agricultural Research Service, when you deprive your body of calories, it turns to its own muscle proteins for fuel, ultimately leading to muscle breakdown. As a result, because of this reduction in muscle mass, you may initially believe that you've lost fat.
Due to this loss of muscle mass, you burn fewer calories, your metabolism slows down and your body actually begins to store fat. "As catabolic metabolism increases, you will have to work harder and harder just to stay even, just to keep from getting flabby," says Stephen Cherniske in "The Metabolic Plan." When muscle mass and physical activity are both on the low side, your body assumes that little energy is required to maintain your musculoskeletal and cardiovascular systems. When this happens, the automatic response of the gastrointestinal tract and liver is to send off any extra calories to be converted into fat.
On the other hand, says Cherniske, if you maintain muscle mass and keep up physical activity, your body's response will be to convert spare calories into energy. The way to prevent catabolic weight loss and subsequent fat gain, then, is to ensure that you not only avoid reducing your calorie intake too quickly, but also that you exercise regularly, both of which will foster a state of anabolism. For a healthy benchmark, Chemiske suggests that you aim to maintain a stable weight loss rate of 1 to 2 lbs. per week, and perform resistance-training exercises at least three times a week. This, in turn, will build lean muscle. Because muscle burns more energy, even while you're resting, you'll burn excess calories and fat throughout the day.