Weight Gainer usually include protein, carbohydrates and fat in a proper ratio that supports increased muscle and lean body mass when used as part of a strength training program. It is a calorie-dense food designed to help one intentionally gain weight. A gainer may be used by athletes, patients suffering from a wasting illness or growth disorder. It is also known as mass gainers or mass builders, are supplements that are designed to help people gain weight. For those who struggle to eat enough during the day, Weight Gainer supplements offer a convenient and effective way to boost calorie intake.