Tired of working out for hours with no results? You need a diet to gain weight and muscle mass. Optimum Nutrition Serious Mass is a delicious blend of ingredients designed to help you bulk up and gain weight. This mass gainer contains 1,250 calories per serving and 50 grams of protein for muscle recovery and bodybuilding. Serious Mass gives you the tools to gain weight and build the body you’ve always wanted. You’ll love this chocolate-flavored powder for building muscle.