Optimum Nutrition Serious Mass is a high quality Weight Gainer Supplement from the world of Bodybuilding and Sports Nutrition. Each serving contains a huge hit of 1250 calories, 50g of protein and 252g of carbohydrates. It is the ultimate weight gainers formula. Optimum Nutrition Serious Mass has been formulated to provide the consumer with all the required tools to seriously pack on the pounds, but in a way that gives you the best physique possible and not just to put on excess fat. It is all about increasing your body’s capacity for lean muscle mass.