Signature Mass Gainer is a simple - and clean - way to go from skinny to stacked. It's fully stocked with 810 calories, 50 grams of muscle-building protein, and 133 grams of carbohydrates. Probiotics help your body utilize the protein to its fullest. So, if you can't seem to get enough mass-making nutrition in your day, skip the drive-thru and have a rich, satisfying shake.