Gaining Muscle Diets - How Many Calories Should Skinny Guys Have?Skinny guys are always trying different gaining muscle diets. They are desperate to get that hot muscle bound body that they see on TV or in some magazine. The problem is that skinny guys face a huge challenge when it comes to packing on muscle and size. This problem is because they burn off all their calories due to their high metabolism. In the fitness world we call these guys a hard gainer because it’s hard to gain muscle mass.