Optimum Nutrition Serious Mass Vanilla (2.73kg). Calorie rich protein source. The ULTIMATE weight gain formula.. Add serious mass with 1,250 quality calories per shake.. Support muscle growth with 50 g of proteins and 250 g of carbs per serving.. Enjoy between meals, post-workout &/or before bed.. Simply mix up 2 scoops with milk or water in your Optimum Nutrition shaker and enjoy between meals, post-workout and/or before bed. Size is an advantage in many sports, but some athletes have a hard time gaining weight. You can only eat so much food. Serious Mass is the ultimate in weight gain formulas, with 1250 calories per serving and 50 grams of protein to support muscle growth and repair.. This instantised powder makes the ideal post work-out and between meals shake for sizing up your goals. Serious Mass provides you with the tools you need to pack on the pounds and when coupled with serious weight room effort - develop your physique to the fullest.