Why milk proteins matter

Lactose intolerance may not be to blame for your post-whey shake stomach ache.

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Cow’s milk can contain two types of protein, A1 beta casein and/or A2 beta casein. Studies have found the former may be associated with more digestive issues, but stores typically sell milk with both proteins (known as A1/A2 milk) because farmers often combine the supply from their entire herd together.

Now, some farms are genotyping cows and selecting those that are A2 homozygous to create milk that only contains A2 protein, since the resulting product may be gentler on the stomach.
Research suggests that A1 protein can lead to abdominal pain, inflammation in the gastrointestinal tract, and other problems. When your body digests the protein it releases beta-casomorphin-7, a peptide that has been shown in animal studies to trigger an inflammatory immune response.

Still, more research needs to be done to figure out what makes someone susceptible and to confirm whether the A2 type is better for you overall, says dairy researcher Ian Givens, Ph.D., director of the Institute of Food, Nutrition and Health at the University of Reading in England. One of his current studies looks at A2 and A1/A2 milks and their connections to gut health, so there may be more answers soon.


If milk makes your stomach ache and lactose-free variations are no better, try switching to the A2 type and see if it has the same effects. The a2 Milk Company has been selling it around the world for years, and now it’s available in many chains like Whole Foods Market and The Fresh Market.