What Is A2 Milk?

This Holstein looks like she's skeptical that the amino acid histidine in her milk may be what's causing digestive issues. (Photo: Sebastian Knight/Shutterstock)

Nearly every grocery chain in Australia carries it. It's sold in New Zealand, China and parts of western Europe. Some dairy farmers in the U.S. are gearing up to bring it to consumers here by next year, according to The Atlantic. I'm referring to A2 milk: Milk from cows with a genetic variation in a protein chain known as A2. The milk's health claims, mostly coming from those who sell it, are impressive. But does the scientific research back them up?

The difference between A1 and A2 milk

Whether you're drinking skim, reduced-fat, whole, organic, reduced-lactose, grass-fed, antibiotic-full or antibiotic-free milk in the U.S., if that milk came from a cow, it is most likely A1 milk, or possibly milk that is a combination of both A1 and A2.

All cow's milk contains beta-casein protein chains. In some cows that protein chain is an A1; in others it's an A2. The two are identical except for one different amino acid at position 67 in the chain of 209 amino acids. At that position the amino acid is histidine in A1. In A2, it is proline.

This video explains the difference in the protein chain and lists the health benefits to people, though the claims come from the a2 Milk Company (A2MC), which made the video.


The part of the video that explains the protein chains in the milk is factual. For example, beta casein makes up 30 percent of the total protein in cow's milk. But then things get iffier. The explanation about the effects on humans likely comes from studies mostly sponsored by those who have a vested interest in the success of A2 milk's sales. According to the Atlantic, "most of the studies that found health benefits from drinking A2 milk were commissioned by A2MC itself."

A2 is not a scientific manipulation of the milk in some cows. In fact, The Atlantic says that A2 is the original protein chain cows probably had, and "the A1 mutation originated in Europe somewhere around 8,000 years ago." Possibly, farmers started selective breeding at this time and cows with the A1 produced more milk. Or, maybe they were just cuter. For whatever reason, breeds like Holsteins that have the A1 mutation became the preferred breeds, and the majority of humans in the Western word have been drinking milk with the the amino acid histidine in it for thousands of years.

A2's health claims

milk, upset stomach
Fans of A2 milk say they have less bloating and fewer stomach issues than when they drink regular milk. (Photo: absoluteimages/Shutterstock)

Sales of A2 milk have done well in other countries as consumers hear about the health benefits of A2. Those benefits not only include less bloating and other stomach issues that often have been attributed to lactose, but also chronic health problems like Type 1 diabetes and heart disease. Huffington Post adds that some claim A1 milk can be the cause of autism and schizophrenia.

Is the science there to back up those claims? Most studies that have shown significant positive results are industry-sponsored, not independent. There is also anecdotal evidence from people who have switched to A2 who say they no longer feel discomfort after drinking milk. For now, the companies selling and marketing the milk are focusing on the "less discomfort" message.

Some artisan dairy farmers in the U.S. are beginning to breed A2 cows in anticipation of demand.

As health trends go, it seems harmless to switch out A1 milk for A2 milk. Whether drinking the A2 will make any measurable difference remains to be proven, but when did that ever stop consumers from latching onto the next big health trend?