Whey protein isolate and whey protein concentrate are the most common types of protein powders used today. The main difference between these two is that isolate has more fat and lactose removed (more pure form of protein), hence it contains more protein per serving basis. Usually as high as 90%.
WPC usually has a protein ratio in the 70-80% range. But most of the studies and feedback from a lot of athletes suggests that the best protein would be a combination of both WPI and WPC. WPI would digest faster and consequently going into your bloodstream first. A more slow digestion of WPC would let it go into the bloodstream later, hence keeps a steady concentration of proteins in your body for a much longer period of time.
Both proteins are very important for your body, since it provides the body with building blocks to produce amino acids and build muscle tissue. There were a few studies suggesting that WPI and WPC do have some substantial benefits for the immune system.
About 15-18 years ago proteins were used almost solely by Bodybuilders and weight lifters, who wished to build lean muscle mass. In the last decade it has changed. It has been shown that almost any athlete or any person that is exercising quite heavily would lose some muscles, when protein levels become depleted.
Now a WPI and WPC combination is widely used by endurance athletes such as bikers, long distance runners, basketball and ice-hockey players, since during their workouts they are often times exercising on depleted levels of proteins.
The best way to use proteins is a split serving of 3-6 times a day, which will allow to keep a constant concentration of protein in your body. Generally, daily intake should not exceed 1gr of protein per 1lbs of body weight (or 2 gr of protein per 1kg of body weight).