According to the literature, more than 10,000 years ago, and before they were domesticated, cows produced only the A2 beta casein protein.1 Around 8,000 years ago a natural gene mutation occurred and was passed on to many breeds.1 Slowly, the A1 beta casein variant became dominant in milk.1 While dairy herds in many parts of the world remain naturally high in cows producing A2 milk, the A1 version of the protein is common among cattle in the Western world.1 Most milk contains a mixture of these proteins.1 The proportion of A2 and A1 beta casein in milk can vary with different breeds of dairy cattle – A2 milk contains only A2 beta casein.1
Intolerance to milk is common, approximately 65 percent of the human population has a reduced ability to digest lactose after infancy.2
Lactose intolerance is an impaired ability to digest lactose, a sugar found in milk and other dairy products.2 Lactose is normally broken down by an enzyme called lactase, which is produced by cells in the lining of the small intestine.2
Lactose intolerance in adulthood is caused by reduced production of lactase after infancy.2 If individuals with lactose intolerance consume lactose-containing dairy products, they may experience abdominal pain, bloating, flatulence, nausea, and diarrhea beginning 30 minutes to 2 hours later.2
What is the connection? A2 milk is a topic of research lately in regards to milk tolerance, the hypothesis is that some people may be sensitive to A1 beta casein protein and not lactose. This means researchers are studying A2 milk to see if those who previously thought they had lactose intolerance would tolerate A2 milk just fine without the gas and bloating!
A 2016 study by Jianqin et al studied 45 subjects with self-reported intolerance to cow’s milk to determine tolerance of A2 milk versus milk with both A1 and A2 beta casein proteins. The authors concluded that consumption of milk containing both types (A1 & A2) was associated with greater worsening of gastrointestinal symptoms and gastrointestinal transit time in lactose intolerant subjects than in lactose tolerant subjects, whereas milk containing only A2 β-casein did not exacerbate these symptoms in lactose intolerant subjects.3 These results suggest that exacerbation of gastrointestinal symptoms associated with milk in lactose intolerant subjects may be related to A1 β- casein rather than lactose.3 However, this was a small crossover study and was funded by The a2 Milk Company Limited, so take this with a grain of salt!
What does all this mean? If you are lactose intolerant, you may want to find A2 milk at your grocery store and give it a try to see if you tolerate it better than traditionally purchased milk. Maybe you are not lactose intolerant after all! Keep your eye out for more research being done that will provide us with better understanding of the different types of milks.
- California Dairy Research Foundation. Accessed 10/26/17. https://cdrf.org/2017/02/09/a2-milk-facts/
- US National Library of Medicine. Accessed 10/26/17. https://ghr.nlm.nih.gov/condition/lactose-intolerance#definition
- Jianqin et al. Nutrition Journal (2016) 15:35 DOI 10.1186/s12937-016-0147-z