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  • Writer's picturefranceswalker@thefoodinto

Why you may tolerate A2 milk

Updated: May 13

Do you react to normal milk but seem to be able to tolerate A2 milk?

If you have found your dairy issue then you are lucky. This is an easy swap without compromising your nutrition.

What are you reacting to in normal milk and what does this mean for other dairy foods such as cheese and yoghurt?

What is A2 Milk?

The difference between normal cow's milk and A 2 milk comes down to A1 and A2 proteins.

A2 Protein

Normal milk and A2 milk both contain a protein called beta-casein. Beta- casein is only one of the proteins in cows milk but it is a major one, accounting for 30% of the milk proteins.

Beta-casein comes in two types of structures: A1 and A2.

The difference is at the 67th amino acid which in A1 beta-caesin is HISTIDINE and in A2 milk is the amino acid PROLINE.

When both these different proteins are broken down in our gut during digestion very different protein fragments are formed.

The A1 β-casein breaks at the 67th amino acid forming the peptide betacasomorphin-7 (BCM-7).

In contrast, break down of the A2 β-casein results results in very little BCM-7 (6).

It is the peptie (short protein) betacasomorphin-7 (BCM-7) that seems to be causing your issues.

How A1 milk produces BCM7

The History

The history of the A1 and A2 is completely fascinating.

Originally, all cow's milk only contained A2 protein.

A MUTATION OCCURRED: around 5000 - 10,000 years ago in the cows of Northern Europe and A1 suddenly appeared in cow’s milk for the first time.

Onto modern times, and regular milk now contaians roughly equal proportions of the A1 and A2 beta-casein.

The proportion can change depending on the genotype of the different cow species or even herds. Only genetic testing can reveal this information with any specific herd.

A2 milk comes from cows that produce more of the A2 than the A1 beta-caesin.

What does this mean for the gut?

Animal and human studies suggest that BCM-7 affects movement of the gut and increases gut inflammatory markers (3, 6).

Limited data suggests that milk containing more A2 protein may make the milk move more quickly through the gut (reduce intestinal transit time) and result in fewer gut issues than milk containing only A1, although more evidence is needed to confirm this (1-4).

It may be of particular interest with those with constipation: based on the small number of human studies which have shown that A2 β-casein shortens gut transit time.

However relatively large intakes may be needed to achieve these effects (2-3 cups of milk per day).

Should you try A2 milk if you seem to be intolerant to normal milk?

A2 milk is safe as long as you do not have a cow's milk allergy (1).

Use the lactose free A2 milk if you think you are also sensitive to the lactose in cow's milk.

Unfortunately cheeses, yoghurts and other dairy products are not available in the same way A2 milk is so these will still have the BCM-7 being porduced in the gut.

Dairy like butter and cream are low in protein so will have lower levels of the BCM-7.

If you get serious side effects from any milk protein, only trial A2 milk with medical advice/supervision.

In people with IBS, or those avoiding dairy due to a suspected intolerance trialling A2 dairy is worthwhile, and if successful will go a long way in making sure you don't over eliminate foods you don't need to in your diet.


  1. Jianqin, S., et al., 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. Nutr J, 2016. 15: p. 35.

  2. Crowley, E.T., et al., Does milk cause constipation? A crossover dietary trial. Nutrients, 2013. 5(1): p. 253-66.

  3. Barnett, M.P., et al., Dietary A1 beta-casein affects gastrointestinal transit time, dipeptidyl peptidase-4 activity, and inflammatory status relative to A2 beta-casein in Wistar rats. Int J Food Sci Nutr, 2014. 65(6): p. 720-7.

  4. Ho, S., et al., 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): p. 994-1000.

  5. Scientific Report of EFSA prepared by a DATEX Working Group on the potential health impact of β-casomorphins and related peptides. EFSA Scientific Report (2009) 231, 1-107.

  6. Ul Haq, M.R., et al., Comparative evaluation of cow beta-casein variants (A1/A2) consumption on Th2-mediated inflammatory response in mouse gut. Eur J Nutr, 2014. 53(4): p. 1039-49.


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