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A1 vs. A2 Milk And Your Health

Milk is mostly proteins, 80% of which is casein. There are over a dozen different types of casein proteins. The most common are A1 and A2 beta-casein.

Reviewed by Dr. Blake Myers, ND

What Are The Differences Between A1 And A2 Milk?

Two bottles of fresh milk with blue straws on wooden background

Cows of northern European ancestry, such as Holstein and Ayrshire breeds, have a high A1 casein content. Cows that originated in southern France and the Channel Islands have high A2 casein content. These breeds include Guernsey, Jersey, and Limousine.

Regularly available milk contains both A1 and A2 beta-casein in various ratios depending on the breed. However, milk that is marketed as A2 milk only contains the A2 variety of casein. Milks from other animals, such as goats, sheep, water buffalo, and camels, are also A2 milks.

Casein is a particularly difficult protein to digest, so you may have snippets of incompletely digested fragments. The key difference between A1 and A2 milk is a single amino acid change that makes the fragments (beta-casomorphin-7) act more like opiates. A1 casomorphins may cause inflammation by interfering with opiate receptors in the gut and immune cells.

beta casein molecule structure
A1 vs A2 beta-casein

Is A1 Casein Inflammatory?

This has been a long debated topic. Research has shown a number of differing results. Some studies show that all casein is inflammatory. While others show that dairy is only inflammatory in those with an allergy or intolerance. 

Still other studies have demonstrated that A1 milk has negative health effects, while A2 does not. Below is a discussion of the possible health impacts of A1 milk.

Possible Health Effects Of A1 Milk

A1 beta-casein may trigger Th2 immune system reactions. Th2 cells are commonly associated with increased allergies, eczema, and asthma symptoms. A1 milk varieties also may stimulate a broad range of other negative immune system reactions and inflammation in the intestines. A2 on the other hand, does not show the same kind of immune reactivity. 

Gut inflammation may lead to leaky gut and contributes to whole-body inflammation. These two factors are at the root of many chronic inflammatory and metabolic diseases. 

Inflammation in the digestive system affects the brain as well. Therefore, A1 milk may negatively impact cognitive performance.

People consuming A1 milk report negative impacts on digestive function. Compared to A2 milk consumption, A1 milk consumption is associated with softer and unhealthy stool consistency. A1 may also contribute to constipation in some individuals, rather than loose stool. Elimination of A1 may improve these symptoms in these studies. 

Lactose intolerance may be less about lactose and more about inflammation. Symptoms of lactose intolerance are improved by the elimination of A1 milk.

A man suffers from abdominal pain while sitting at home on the couch.

What You Can Do About A1 Milk 

If you are going to continue to consume dairy products, it is wise to figure out if you have any sensitivities to A1 beta-casein. To do this, eliminate all dairy for at least 2 weeks (washout). See how you feel and pay attention for any chronic symptom improvements during this time. 

After the washout period, drink regular milk on one day. Over the next 3 days, symptoms should flare if you are sensitive to any component of the milk. In this case, repeat the washout for 2 weeks and rechallenge with A2 milk. If you react to regular milk, but have no reaction to A2, it may be that A1 casein is a problem for you and A2 is not.

You can also simply choose to switch to A2 milk and see how you feel over the long term.


Reducing inflammation in any way possible is a worthwhile endeavor. Switching from A1 to A2 milk may be a supportive measure you can take to improve digestive function and gut inflammation. Ensuring optimal casein digestion with Gluten Guardian is an additional stop you can take to protect yourself from the inflammatory effects of casein in your diet.

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  1. Kuellenberg de Gaudry D, Lohner S, Bischoff K, et al. A1- and A2 beta-casein on health-related outcomes: a scoping review of animal studies. Eur J Nutr. 2022;61(1):1-21. doi:10.1007/s00394-021-02551-x
  2. Woodford KB. Casomorphins and gliadorphins have diverse systemic effects spanning gut, brain and internal organs. Int J Environ Res Public Health. 2021;18(15):7911. doi:10.3390/ijerph18157911
  3. Ul Haq MR, Kapila R, Sharma R, Saliganti V, Kapila S. Comparative evaluation of cow β-casein variants (A1/A2) consumption on Th2-mediated inflammatory response in mouse gut. Eur J Nutr. 2014;53(4):1039-1049. doi:10.1007/s00394-013-0606-7
  4. Ho S, Woodford K, Kukuljan S, Pal S. Comparative effects of A1 versus A2 beta-casein on gastrointestinal measures: a blinded randomised cross-over pilot study. Eur J Clin Nutr. 2014;68(9):994-1000. doi:10.1038/ejcn.2014.127
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