Whey protein is highly bioavailable, rich in essential amino acid (including leucine), and quickly digested. Consuming whey causes a larger increase in blood amino acids than does casein or soy protein. And, both at rest and after exercise, whey protein stimulates muscle protein synthesis (MPS) to a greater degree than casein and soy — likely due to the quicker digestion and/or higher leucine content of whey hydrolysate.[1]