| What I've heard supposed by the bodybuilder types is insulin (or insulin raising food really) combined with protein is the perfect post-workout combination.
The insulin (or insulin producing foods) causes your cells to open up and feed. While they are open, the fast-digesting protein found in most protein shakes slide right into the muscle cells. Supposedly this reduces catabolism and increases muscle mass because your body is in the right frame of mind to soak up much of the protein being thrown at it due to the amount of energy expenditure during the workout. | 
