Last year, before I even touched gear, I decided to diet off my gut. I was big, at 195# (well, big for 20 y/o and no gear), but still had that gut.
Still, completely clean, I went on a diet. My only carbs were complex carbs an hour before my workout and sugar right after. I had protein every three hours. I did intense cardio 4 mornings a week. I did e every weekend (which, as long as you stay hydrated, helps burn fat). My weight went from 195 to, well, 195, but I lost a significant amount of fat. Didn't measure the percentage, but got plenty of comments from people.
This means that, even not on anything (but 20 years old is a time of high natural testocerone levels anyway), I gained the same amount of weight in muscle that I lost in fat.
Maybe I genetically have a slow metabolism, and a lot of the extra calories were superfluous and not necessary for growth, and the cardio and dieting just shaved those calories off.