A2 milk is cow’s milk whose beta-casein protein is only the A2 type. In two small trials, people who said ordinary milk bothered them reported less digestive discomfort on A2-only milk. Both trials list an author from an A2 milk company, and Europe’s food safety authority found no established link between the A1 protein and any disease. Here is what each study measured.

What A1 and A2 mean

Most cows’ milk carries two types of a protein called beta-casein: A1 and A2. The difference matters at one point in the protein. When the A1 type is digested, it can release a peptide called beta-casomorphin-7, usually written BCM-7. The A2 type has a proline at position 67 of the protein, which makes that split less likely. Human breast milk beta-casein is also of the A2 type.

“A2 milk” on a carton means milk from cows whose beta-casein is the A2 type only.

The 2016 trial: 45 adults

Forty-five Han Chinese adults who reported lactose intolerance drank ordinary milk (both types) for 14 days and A2-only milk for 14 days, in random order, with 14 days without dairy at the start and between the two. Neither they nor the researchers knew which milk was which.

On ordinary milk, they reported more digestive discomfort after drinking it than on A2-only milk. On A2-only milk, their symptoms were no worse than at the start of the trial. The researchers also recorded longer gut transit times and higher levels of BCM-7 on ordinary milk.

One of the six authors is listed at The a2 Milk Company Limited. The study is Jianqin and colleagues, Nutrition Journal, 2016.

The 2014 pilot: 41 adults

Forty-one adults drank 750 ml a day of each milk for two weeks, after two weeks on rice milk, in a blinded crossover lasting eight weeks. Stool consistency differed between the two milks, and abdominal pain tracked stool consistency on A1 milk but not on A2 milk.

The authors called these results preliminary and wrote that they “require confirmation in a larger study”. One author is listed at A2 Dairy Products Australia. The study is Ho and colleagues, European Journal of Clinical Nutrition, 2014.

What has not been shown

You may have read that A1 milk causes type 1 diabetes or heart disease. In 2009 the European Food Safety Authority reviewed the research on BCM-7 and concluded that “a cause-effect relationship between the oral intake of BCM7 or related peptides and aetiology or course of any suggested non-communicable diseases cannot be established.” It found that the country-by-country comparisons behind those ideas “cannot provide a proper base to demonstrate a cause-effect relationship”.

A 2017 paper that argues for a link to type 1 diabetes says the same about its own case: “causation remains unproven”. Its editing was paid for by The a2 Milk Company, and three of its seven authors declare past ties to that company.

Who the trials were about

Both trials studied adults who said ordinary milk bothered them. They lasted two weeks per milk. Neither tested children, and neither tested anyone over months or years. If milk gives you trouble, a doctor or a registered dietitian can tell you whether lactose, the A1 protein or something else is the cause.

Sources

• Jianqin S, Leiming X, Lu X, Yelland GW, Ni J, Clarke AJ. 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. 2016;15:35. PubMed 27039383
• 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. European Journal of Clinical Nutrition. 2014;68(9):994-1000. PubMed 24986816
• European Food Safety Authority. Review of the potential health impact of β-casomorphins and related peptides. EFSA Journal. 2009;7(2):231r. doi:10.2903/j.efsa.2009.231r
• Chia JSJ, McRae JL, Kukuljan S, Woodford K, Elliott RB, Swinburn B, Dwyer KM. A1 beta-casein milk protein and other environmental pre-disposing factors for type 1 diabetes. Nutrition & Diabetes. 2017;7(5):e274. PMC5518798

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