Originally Posted by GuitarBizarre

You don't need fat. You need nutrients in your system with which your body can build new muscle tissue. That CAN be achieved by converting excess fatty tissue, but once you're lean, there's no other way to gain muscle than to be taking in more calories than you burn so that your body can convert that extra protein to muscle mass the next workout around. It'll technically be fat for a bit, but you'll never notice it.