Whey protein is a very high quality source of protein that, along with casein, are the major proteins in milk. It has all the essential amino acids and therefore scores very high on all methods used to score protein quality.
Whey protein is rich in the amino acid leucine that promotes protein synthesis. Whey also contains a healthy dose of cysteine that increases synthesis of the antioxidant glutathione, a major fighter of free radicals.
Other research indicates that whey can decrease appetite and improve body composition by enhancing lean muscle tissue and decreasing fat. A recent report found that whey protein increased glycogen levels in both the liver and skeletal muscle of exercise-trained rats more so than other types of protein. Glycogen is a crucial energy source to perform high intensity exercise.