Also known as mass gainers, weight gainers are designed to help users add calories to their diet, increase muscle mass and promote weight gain. They are high in protein, as well as carbohydrates, fats and (sometimes) amino acids. When people wish to gain mass, they must consume more calories than they burn every day. Weight gainers are sold as a way to help you gain all the nutrients you need without the bloating or discomfort that can come from eating a large meal. The weight-gainer products reviewed in this section could be available in powders, or in ready-to-drink and capsule forms.