Bodybuilders often take a powdered form of protein, the essential building blocks for muscle. Protein powder is generally consumed immediately before and after exercising, or in place of a meal. The theory behind this supplementation is that having a sufficient protein intake allows for efficient growth and repair of muscle tissue.

* Whey protein is the most commonly used type of protein. It is absorbed by the body very quickly and easily. It contains high levels of all the essential amino acids, branched-chain amino acids and has the highest content of the amino acid cysteine which is important for the biosynthesis of glutathione; which has extremely important immune boosting properties for the body.

* Casein protein (or Milk protein) is the richest in glutamine, an amino acid that aids in recovery, and has casomorphin which helps the body to absorb the amino acids over a long time.

* Soy protein contains all essential amino acids, and is an alternative protein for vegetarians. Soybeans also contain isoflavones, a type of phytoestrogen, which have a weak estrogenic activity.

* Egg white protein is a lactose- and dairy-free protein.

* Hemp seed contains complete and highly-digestible protein and hemp oil is high in essential fatty acids.

source from : http://en.wikipedia.org/wiki/Bodybuilding_supplement