Milk contains both whey and casein proteins. Casein proteins come in different varieties including a specific type called beta-casein. Cows’ milk can contain up to 12 types of beta-casein! The relevant types of beta-casein in cows’ milk are A1 and A2.
The breed of the cow determines what types of beta-casein are contained in cows’ milk. Cows can produce purely A2, A1, or A1/A2 hybrids of beta-casein protein. A2 protein milk and A2 protein formula contain only A2 beta-casein protein because they come from cows producing only this type. Some people say they feel more comfortable after drinking the A2 protein only milk compared to standard cows’ milk(1,2).
- Jianqin, S., Leiming, X., Lu, X., Yelland, G. W., Ni, J., & Clarke, A. J. (2015). Effects of milk containing only A2 beta casein versus milk containing both A1 and A2 beta casein proteins on gastrointestinal physiology, symptoms of discomfort, and cognitive behavior of people with self-reported intolerance to traditional cows’ milk. Nutrition journal, 15(1), 35.
- Milan, Amber M., Aahana Shrestha, Helga J. Karlström, Jakob A. Martinsson, Nils J. Nilsson, Jo K. Perry, Li Day, Matthew PG Barnett, and David Cameron-Smith. “Comparison of the impact of bovine milk β-casein variants on digestive comfort in females self-reporting dairy intolerance: a randomized controlled trial.” The American journal of clinical nutrition 111, no. 1 (2020): 149-160.