If you aren’t lactose intolerant (or aren’t sure) and haven’t been diagnosed with a milk allergy, the culprit could be a specific protein in your milk called A1 beta-casein.

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On Nutrition

Is there more to milk sensitivity than lactose intolerance?

Do you have trouble digesting cows milk? If you aren’t lactose intolerant (or aren’t sure) and haven’t been diagnosed with a milk allergy, the culprit could be a specific protein in your milk called A1 beta-casein.

Casein is the main protein in cows’ milk. Beta-casein, one type of casein, comes in two forms, A1 and A2, that are almost identical — but not quite. Some scientists say this slight variation might cause certain people to digest them differently.

According to the New Zealand-based A2 Milk Company, some people who think they are intolerant to lactose, the natural sugar in milk, may actually be intolerance to the A1 protein, making A2 milk a healthier alternative.

What’s old is new again

Once upon a time, all milk was A2 milk. A1 beta-casein is the result of a genetic mutation that appeared a few thousand years ago in some European dairy herds. Today, a cow’s genes determine which type of beta-casein is in her milk. Each cow inherits a copy of the beta-casein gene from both parents, so modern cows can be purely A2, purely A1, or an A1/A2 hybrid.

Most milk available in the United States comes from Holstein Friesian cows — the world’s most popular dairy-cattle breed — and contains an equal mix of A1 and A2 beta-casein.

The Guernsey and Jersey cows, as well as African and Asian cattle breeds, produce mostly A2 beta-casein. Based on the theory that A1 beta-casein may cause health problems, farmers in New Zealand and Australia started converting their herds to A2-producers about 15 years ago. In the United States, this trend is just beginning, and Cherry Valley Dairy in Duvall is one local farm that’s onboard.

Cherry Valley produces artisanal cheese, butter and milk from its small herd of around 40 pastured Jersey cows. Typically, converting a dairy herd starts with genetic testing of existing cows and continues with a breeding program using semen from pure A2 bulls. It takes about 10 years for farmers to gradually convert their dairy herds to pure A2, but costs are minimal.

Because they are Jersey cows, two-thirds of Cherry Valley’s herd may already produce A2 beta-casein. Farm manager AnnMarie Stickney said the dairy is opting to not genetically test their cows, but is using A2 bulls to produce the next generation. “All of the heifer calves are going to have at least one copy of the A2 gene. I would imagine that over time we’d have a higher percentage of A2 cows.”

Cherry Valley’s Dairy Reserve cheese earned a top award in 2014 from the American Cheese Society. Casein, lactose and butterfat are essential for cheese’s structure, flavor and aromatics, said head cheesemaker Blain Hages, and having a higher percentage of A2 milk shouldn’t make a difference. “30 percent of a good cheese comes from aromatics, 70 percent comes from good cheesemaking,” Hages said, and the farm’s pasture and microclimate play a critical role in the aromatics.

What the science says

Proteins are made up of long chains of amino acids. Of the 209 amino acids in beta-casein, A1 and A2 have 208 in common. This tiny difference means that we digest the two types of beta-casein differently. When we digest A1 beta-casein, a protein fragment called beta-casomorphin-7 (BCM-7) is released. It is BCM-7 that may contribute to health problems in certain people, according to some scientists.

It has been speculated that diets higher in A1 beta-casein may contribute to the development of type 1 diabetes, heart disease and autoimmune conditions like asthma and eczema, but there is no conclusive scientific data.

One cup of milk contains about ½ teaspoon of beta-casein, and a small 2014 study did find that some people who experience abdominal pain and loose stools after drinking A1 milk don’t have the same problem after drinking A2 milk.

Who shouldn’t try A2 milk? Anyone who has been medically diagnosed with a cows milk allergy or lactose intolerance. Who might want to try A2 milk? People who suspect they are lactose intolerant but who have never been tested for it, or people that can tolerate small amounts of cows’ milk before experiencing digestive issues. Of course, if you already digest milk just fine, A2 milk will be no different.

At least a few other Washington dairies are pursuing A2 breeding programs, while some have Guernsey herds who naturally have low levels of A2 beta-casein. Hages said a lot of thought went into Cherry Valley’s decision to convert their Jersey herd to A2-producers. “I think setting the bar higher is a good thing. If I can make someone feel better about drinking milk, it’s worth it.”

He adds that people who might have trouble tolerating A1 milk may benefit by seeking out smaller dairies like Cherry Valley that don’t pool their milk with milk from other dairies — standard practice in large-scale milk production. “It’s a choice that they may be willing to pay more for,” he said. “I believe they should have the right to choose.”