What Is A2 Milk?

A2 milk is cow's milk that contains only the A2 type of beta-casein protein, one of the major proteins found in milk. Most conventional milk contains a mix of A1 and A2 beta-casein proteins. The difference comes down to the cows — certain breeds (like Guernsey, Jersey, and most Asian and African cattle) naturally produce A2 milk, while the dominant Holstein breed used in most U.S. dairy operations produces a mix of A1 and A2.

Why It Matters

Many people who experience digestive discomfort from drinking milk assume they are lactose intolerant. But a growing body of research suggests that for some of these people, the problem is not lactose at all — it is the A1 beta-casein protein.

When A1 beta-casein is digested, it releases a peptide called beta-casomorphin-7 (BCM-7). Some research has linked BCM-7 to digestive discomfort, including bloating, gas, and altered stool consistency — symptoms that mimic lactose intolerance. A2 beta-casein does not release BCM-7 during digestion.

This matters because people who have given up milk due to digestive issues might actually tolerate A2 milk without problems. It also raises broader questions about how modern dairy breeding — which prioritized the high-producing Holstein at the expense of heritage breeds — may have inadvertently changed the protein profile of our milk supply.

How It Works

All cows produce beta-casein protein, but the exact type depends on the cow's genetics. The two most common variants are:

A1 beta-casein: Found predominantly in milk from Holstein-Friesian cattle, the breed that dominates commercial dairy in the U.S., Europe, and Australia. When digested, A1 releases the peptide BCM-7 at position 67 of its amino acid chain, where it has a histidine residue.

A2 beta-casein: Found in milk from older breeds like Guernsey, Jersey, Brown Swiss, and most cattle from Africa and Asia. A2 has a proline at position 67 instead of histidine, which prevents the release of BCM-7 during digestion.

To produce A2 milk commercially, dairy companies genetically test their herds and separate A2-producing cows from A1 producers. The milk itself is not modified — it simply comes from cows that naturally carry two copies of the A2 gene.

The research: A 2016 study published in Nutrition Journal found that participants drinking A1 milk reported more digestive discomfort and had longer gut transit times compared to those drinking A2 milk. Several other studies have shown similar results. However, the body of evidence is still relatively small, and some researchers argue the studies have been too heavily funded by A2 milk companies to draw firm conclusions.

What to Watch Out For

• A2 milk is not lactose-free. If you are truly lactose intolerant (lacking the lactase enzyme), A2 milk will still cause problems because it contains the same amount of lactose as regular milk. A2 is only relevant if your issue is with the protein, not the sugar.
• The science is promising but not settled. Most studies showing A2 benefits have been funded by The a2 Milk Company or related entities. Independent research is limited but growing. The mechanism is plausible, but more large-scale, independently funded studies are needed.
• Heritage breed milk is naturally A2. If you buy milk from a farm raising Guernsey, Jersey, or similar heritage breeds, you are likely already getting A2 milk without paying for the branded version. This is one advantage of knowing your local dairy farmers.

The Bottom Line

A2 milk is a legitimate option for people who experience digestive discomfort from conventional milk but test negative for lactose intolerance. The science behind it is plausible and supported by some clinical evidence, though the research base is still developing. If milk has always bothered your stomach, it is worth trying A2 milk to see if the protein, not the lactose, was the issue all along.

Frequently Asked Questions

Is A2 milk healthier than regular milk?

A2 milk has the same nutritional profile as conventional milk — same calories, protein, fat, calcium, and vitamins. The only difference is the type of beta-casein protein present. A2 is not "healthier" in a general sense; it may simply be easier to digest for certain people.

Why do older cattle breeds produce A2 milk?

All cattle originally produced A2 milk. A genetic mutation thousands of years ago introduced the A1 variant in European cattle. The A1 gene became dominant in the Holstein breed, which was selectively bred for high milk volume and became the world's dominant dairy breed. Heritage breeds that were not subjected to the same selection pressures retained the original A2 genetics.

Can I tell the difference between A1 and A2 milk by taste?

No. A1 and A2 milk taste the same and are visually identical. The only way to determine a cow's beta-casein type is through genetic testing. You cannot identify A2 milk by appearance, taste, or texture.