Insulin is a highly anabolic hormone that promotes amino acid transport into muscle cells and triggers processes involved in muscle protein synthesis.  A Japanese study found that consuming eight grams of whey protein and 17.5 grams of carbohydrate after exercise increased insulin and blood amino acids more than consuming carbohydrate alone or lesser amounts of protein.  Post exercise consumption of whey protein increases blood amino acids and the anabolic hormone insulin, which promotes muscle protein synthesis.  (European Journal Sports Science, 12:152-160, 2012)