Optimum Nutrition Serious Mass Weight Gainer in 7 Great Flavours. Optimum Nutrition Serious Mass contains Maltodextrin, Glutamine, Creatine as well as a vitamin and mineral blend. With 1,250 calories per serving to boost daily calorie intake, 50g high protein to support muscle growth and repair, over 250g carbohydrates helping support muscle recovery, and now with 3g added Creatine to support performance per serving, you’ve got nothing to lose and lots to gain.