Optimum Nutrition Serious Mass is a high-protein muscle building and weight gainer protein powder. Each serving provides 1,250 calories, 50 grams of blended protein, and over 250 grams of carbohydrates with no added sugar. It also includes essential vitamins and minerals such as Vitamin C, Zinc, and Vitamin D for immune support. This product is ideal for post-workout and between meals to help you achieve your muscle gain goals.