The use of whey proteins, as a source of amino acids and its effect on reducing the risks of diseases such as heart disease and cancer, is the focus of ongoing research. Whey is a source of branched chain amino acids (BCAAs) which are used to fuel working muscles and stimulate protein synthesis. Whey contains high amounts of BCAAs. In particular, leucine plays a key role in initiating the transcription pathway that fires up protein synthesis. When leucine is ingested in high amount, such as with whey protein supplementation, there is greater stimulation of protein synthesis, which may speed recovery and adaptation to stress (exercise).
Whey protein contains the amino acid cysteine which can be used to make glutathione. However, this amino acid is not essential for the synthesis of glutathione and some studies have suggested that the amount of cysteine in the diet may have little effect on glutathione synthesis. However, another study suggested that large amounts of whey protein can increase cellular glutathione levels. Glutathione is an antioxidant that defends the body against free radical damage and some toxins, and studies in animals have suggested that milk proteins might reduce the risk of cancer.