The two most common types of beta casein proteins found in milk are A1 and A2. The two proteins are digested differently, and some stomachs have a sensitivity to the A1 protein, causing problems with digestion. Many people who think they are reacting to the lactose in milk, are actually reacting to the A1 protein! Breeds of cows like the Guernsey, can be bred to produce milk without the A1 gene: A2A2 milk. Simply switching to A2A2 milk can reintroduce you back into the world of real dairy products.