When someone moves from India to USA they cannot believe the low cost and abundance of milk until they developed digestive problems. Why this happens?

A1 and A2 milk contain different types of a protein. One of those called beta-casein. Basically caseins are similar to pearls necklace where all pearls are attached to each other. A1 and A2 beta casein are similar to each other except one pearl, that is 67th number in chain.A1 has Histidine and A2 has Proline on 67th number.

Proline has high affinity with neighboring pearls. So it does not let chain break easily. But in case of A1 milk, histidine breaks easily and create chain, called BCM-7. When digested, A1 beta-casein releases beta-casomorphin7, an opioid with a structure similar to that of morphine.

BCM7 is suggested to be associated as a risk factor for human health hazards as it can potentially affect numerous opioid receptors in the nervous, endocrine and immune system.

Epidemiological evidences claim that consumption of beta-casein A1 milk is associated as a risk factor for type-1 diabetes, coronary heart disease, arteriosclerosis, sudden infant death syndrome, autism, schizophrenia etc.

Populations, which consume milk containing high levels of β-casein A2 variant, have a lower incidence of cardiovascular disease and type-1 diabetes.

Although evidences against A1 milk are growing, Moral from this article that it is safe to consume A2 milk than A1.