You must know your body so you can make adjustments , and that's it bro. So you know what works better for you, what kind of workout, how much rest between sets, what foods to avoid , what foods is better to eat, I avoid foods that some people can eat normally, that's it. On Lee Priest channel on youtube where people send him questions all the time, he seems also not to believe in endo, meso, ecto as well, but, there is another video from him when he talks about diet he uses the words "carb sensitive" when talking about diet, he said , "if you are carb sensitive keep your carbs low", some people are not as carb sensitive as other,s of course, so, you must know your body , that's it. Some people take lots of steroids and don't get huge also. Lee Priest was the one the says he was taking few steroids back when he was competing.