Optimum Nutrition has been helping performance-focused athletes for over 35 years achieve their goals. Serious Mass is the ultimate muscle-building and mass gainer formula. Every serving of this mass gainer contains 25 essential vitamins and minerals (including vitamin D, B12, E, Biotin and Magnesium), over 1,250 calories to boost your calorie intake, 50 grams of protein to support muscle growth and 250 grams of carbohydrates helping support muscle recovery .