Whey Protein Isolate is the highest yield of protein currently available, it's a derivative of milk protein. Its short chains and peptides make it available for absorption within ten minutes of ingestion sometimes. It's kind of a protein booster. If you asked which protein is best to invest in WPI would be it. No sane nutritionist would tell you otherwise. Whey is the best investment because of its capacity as a post-workout recovery supplement. That critical time after severe physical stress when the cells will act like a sponge and take in almost anything. The extreme hunger of the cells and the fast-acting properties of whey will make sure you use the best window for recovery to the fullest. If not, the body will hunt the stored reserves of nutrients and when on a diet for example that will cause them to rob other muscle-tissue of glutamine.
So whey is the best protein, especially on a diet. It also supplies the most aminos bodybuilders use. Whey protein is the only choice when on a diet. When on low-carb diets whey can function as an alternate source of energy, sparing hard-earned muscle protein and glutamine stores within the body