Proteins can be categorized into 3 release rates: fast, medium and slow. The debate as to which is best for athletes has been a heated one in recent years. The truth is that combining all of the protein types is ideal!
Crystal Structure of Protein
Fast release proteins: Increase blood amino acid levels rapidly, but amino acid levels also fall rapidly. Sources: Whey protein isolate, whey protein concentrate.
Medium release proteins: Take a little longer to raise blood amino acid levels and drops slower. Sources: Milk protein isolate, soy isolate, soy concentrate.
Slow release proteins: Provide a gradual increase and maintain blood amino acid levels for a longer duration of time. Sources: Casein, whole foods.