> Let's say I'm 6'3 and 300 lbs and I want to convert my belly into muscle mass. Do I need to worry about getting calories or will my body simply use the excess fat to create the muscle? <br> <br>Fat is stored energy, and muscles are built from protein, being mainly made up of proteins themselves. You can convert protein to glucose (energy), but not reverse the preceedure. So no, you can't convert fat into muscle. <br> <br>However, muscles require energy just to maintain them, and you can use fat to do this. Remember though, muscles can be used for energy too are much more readily avaliable than fat. So you must keep up a good weight lifting routine, and fairly steady protein intake. If your muscles are constantly being used, you body isn't going to start destroying them for energy. <br> <br>Don't starve yourself either. Sitting a few hundred calories under your daily expenditure should be more than enough to start dropping pounds, but don't expect anything quick. Weight loss takes time, something people seem to forget.