Whey protein isolate (WPI) is the most pure and concentrated form of whey protein available. It contains 90% protein and very little (if any) fat and lactose. Whey protein concentrate (WPC) has around 70% protein, and higher fat & lactose levels. As the protein level in whey protein concentrate decreases the amounts of fat and/or lactose usually increase.

WPI is a superior product to WPC in many ways, including taste and palatability. WPI mixes into liquid better, so is the better choice for shakes.