Optimum Nutrition Serious Mass 2.73kgSerious calories are needed for serious weight gain. A fast paced lifestyle, a highly active metabolism, and an intense desire to gain weight can make it difficult for many people to get enough calories from complete foods on their own. The best formula for weight gain is Serious Mass. You have everything to gain and nothing to lose with 1,250 calories per serving, 50g of high quality protein to support muscle growth and repair, over 250g of