In the fitness and medical fields it is generally accepted that protein after exercise helps build the muscles used. Whey protein is one of the most popular protein sources used for athletic performance.[4] Other protein sources include egg albumen protein and casein, which is typically known as the slow digestive component of milk protein.[5] Alternative protein bars may use insect protein as an ingredient. Vegan protein bars contain only plant-based proteins from sources like peas, brown rice, hemp, and soybeans.[6]