Beta-casein is a type of protein found in milk, particularly in the milk of cows, goats, and sheep. It is one of the main components of casein, which makes up about 80% of the protein in cow's milk. Beta-casein exists in different forms, known as variants, which can influence how it is digested and how it affects health. Research suggests that the different variants of beta-casein may have varying effects on digestion and may be linked to certain health outcomes. For example, some studies indicate that the A1 variant may be associated with digestive discomfort in some individuals, while the A2 variant is often marketed as being easier to digest.