When it comes to optimally building lean muscle, 100-Percent whey protein is NOT THE KING like you've been led to believe. It is important to consume both whey and casein protein together. That is why SELECT PROTEIN is formulated with Milk Protein Isolate, the first ingredient of formula, which is comprised naturally of both casein and whey protein. This combination acts in a way that 100-Percent whey protein cannot. This is the science SELECT PROTEIN is formulated form a combination of the highest quality Milk Protein Isolate and Why Protein Concentrate 80-Percent.