A scientist from New Zealand began studying the properties of milk in the 1990s to answer the question of why certain people have adverse reactions to milk. Dr. Corran McLachlan discovered that different types of cows produce milk with differing proteins, including what are called A1 and A2 beta casein proteins. He also learned that adverse reactions (such as mucus, irritable bowel syndrome, and bloating) seemed to be associated with the A1 protein. People who suffered from these symptoms after drinking milk containing only the A1 protein did not suffer the same symptoms after drinking milk containing only the A2 protein. A recent scientific study (European Journal of Clinical Nutrition, June 2014) indicates that there is, in fact, a difference in how A1 and A2 proteins are digested. Scientific peer-reviewed studies are appearing more and more frequently as news of this discovery spreads. To date there are more than 100 such studies, a few of which are noted below.
The symptoms of A1 protein tolerance are similar to the symptoms of lactose intolerance, which has the potential to create confusion. Lactose intolerance is caused by a reaction to the sugar (lactose) in milk. While about 25% of people in the US report having digestive issues with milk, only about 5% would be medically diagnosed as being lactose intolerant. For the rest, the issue may well be A1 protein intolerance.
Different cows naturally produce milk with different protein structures, so normal dairy milk has a mixture of A1 and A2 proteins. Dr. McLachlan discovered that all cows originally produced only the A2 protein, and that the A1 protein emerged later in Europe and then spread throughout the western world.Pure ancient breeds, such as the Indian Brahman breed, are still producing only the A2 protein. But as cross-breeding with imported breeds takes place, the A1 beta casein protein trait is showing up more and more even in India. Protecting the purity of the Brahman breed is important so that the purity of the A2 protein can be preserved.
In the US, a few people in the dairy industry are taking steps to breed the A1 protein out of their herds through genetic makeup screening and select breeding. Many have learned about the A1/A2 issue by reading Keith Woodford's book Devil in the Milk. These dairies obtain DNA samples from a representative population of their herds, conduct A2 genotype screening, and then selectively breed to increase the presence of the A2 protein and decrease the amount of A1 beta-casein in their milk products.