For those who are new to the gym scene or even those who are skinny hard gainers, a mass gainer is an excellent tool that you can use to bust through the genetic walls that hold you back from putting on that much needed size. Packed with a healthy dose of protein and energy stimulating carbohydrates, mass gainers work by providing you with the calories needed to help you get in enough materials for your body to pack on some good muscle and size. For those who have the metabolism of a furnace, mass gainers do wonders by providing the body with more than it can burn off, leaving you with enough left over to use for new muscle growth.