Whey is left over when milk coagulates and contains everything that is soluble from milk. It is a 5% solution of lactose in water, with some minerals and lactalbumin. It is removed after cheese is processed. Whey is an abundant source of branched-chain amino acids (BCAAs),which are used to fuel working muscles and stimulate protein synthesis.In particular, leucine plays a key role in initiating the transcription of protein synthesis.When leucine is ingested in high amounts, such as with whey protein supplementation, there is greater stimulation of protein synthesis, which may speed recovery and adaptation to stress (exercise).