The idea is that you can only put on a very small amount of muscle mass as a natural (unless you are a true beginner). So if you eat more most of your "growth" will be fat. It can seem like muscle because gaining a little bit of fat will not make you visibly less cut, it is only after you have really porked up that you notice that most of your gains were fat. Arvilla, Adonis, BAST, or any of the other naturals who have actually dieted down here will confirm this for you.