We looked into the science.
Growing up, I loved milk. I drank it at dinner. I drank it at breakfast. I drank it with cookies—only Europeans and monsters don't. But by my late 20s, a glass of milk could bring on a hellish, bloaty stomach ache, and more than that would absolutely wreck me. I figured I was one of a quarter of Americans who self-report as lactose intolerant.
But about all those people: Researchers, on behalf of New Zealand's a2 Milk Company, say most of these self-reporters aren't lactose intolerant at all, but rather that they have trouble digesting one of the proteins in most North American milk, called A1 beta-casein. According to these researchers, these people would be fine if they drank milk containing only A2 beta-casein proteins—otherwise known as A2 milk.
Since the a2 Milk Company debuted on the US's West Coast in 2015, expanded to the Southeast, and expanded again to the Northeast in January 2018, it's become regular stock at Whole Foods, Publix, Safeway, Target, and The Fresh Market. The a2 Milk Company’s marketing is basically as follows: “Hey, people who think you’re lactose intolerant. Many of you are not actually lactose intolerant. You have a sensitivity to A1 protein, so you just need to be drinking the right kind of milk. Our milk.”
Sounds ultra promising for the milk-challenged hoards like me. But despite glowing testimonials, a2's claims are underpinned by very weakly drawn scientific data.
Lactose intolerance is when the body doesn't produce the enzymes needed to digest milk. Mammals become less tolerant of milk as we ease into adulthood because our bodies stop producing the enzyme lactase. Why wouldn't we? Milk is baby food. So some degree of lactose intolerance is natural for the vast majority of adult mammals.
People started drinking milk as adults 7,500 years ago in Central Europe and underwent a genetic mutation that let them produce lactase into adulthood. The standard theory among dairy scientists is that Europeans living closer to the Arctic Circle needed milk's vitamin D to compensate for the short days' lack of vitamin-D-carrying sunlight, but other researchers point out pockets of lactose tolerance that evolved in West Africa, the Middle East, and South Asia. What they do agree about is that most people in the world lose at least part of their ability to digest milk after infancy. More than 90 percent of East Asians are at least somewhat lactose intolerant, for example. But now even people with milk-tolerant genetics blame it for digestive problems. Only 1 or 2 percent of the West's population avoided milk in the 1980s, says Dennis Savaiano, a dairy scientist at Purdue University. Today, it's 15 to 20 percent.
Of course, A2 milk proponents claim that many of these people are tolerant of lactose and don’t need to avoid all milk, just A1-containing milk.
Prior to a genetic mutation in Europe 5,000 to 8,000 years ago, cows' milk contained only A2 protein, like human breast milk. Certain breeds, such as the Jersey, Brown Swiss, and Guernsey cows common to Europe, Africa, and Asia, still produce milk made mostly of A2 proteins. But the Northern European cows bred to weigh over a thousand pounds, such as the Shorthorn, Ayrshire, and Holstein, contain a roughly even split of A1 and A2 protein, according to Mike Van Amburgh, a dairy scientist at Cornell University. North America likes its cows like its pickup trucks—bigger is better—and A1-rich Holsteins dominate American and Canadian milk production because they produce so much more milk per cow than smaller breeds.
As the a2 Milk Company tells it, their cows produce only A2 proteins. It points to breeding efforts to separate A2-rich individual cows into their own herds, which creates A2-rich and A2-only offspring. “We have found, over our 10 years of working with farmers and cows, about one-third of every herd is A2/A2-producing no matter what breed,” says Blake Waltrip, CEO of the a2 Milk Company’s US operation.
There is always A1 and A2 produced together, Van Amburgh says—it's metabolic flexibility in the cow. “So several dairies that want to sell A2 milk test the cows, segregate the herd, and add another bulk tank so the A2 milk can be separated out,” he adds.
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All across the a2 Milk Company's website are testimonials from people who say they developed dairy issues when they moved to the US, or when they ditched the family dairy cow for store-bought milk, or just got older, and now they can drink A2 milk without stomach rebellion. But the scientific consensus isn't there: “I cannot support their claims as a dairy scientist, based on the evidence supplied,” Van Amburgh says. “It's a very complicated charge the company has made, but overall there is no convincing evidence that humans have a harder time digesting [A1 milk] due to a protein allergy. They've tried to take small data sets from particular countries with small numbers of people and merge them into a coherent meta-analysis.”
Most studies on A1 and A2 proteins, if not close to all, have been funded by the a2 Milk Company or dairy industry trade groups that oppose it. And of those, only three have been performed on humans: two Chinese, in 2014 and 2017 and one Australian, in 2016. Two of the three had small sample sizes of 45 and 41 participants, respectively. And the Chinese studies tested ethnic Han Chinese, part of that famously lactose-intolerant East Asian population we mentioned earlier, and whose results may not be representative of other populations. The Australian study noted a correlation between consuming A1 milk and abdominal pain, but concluded that it “requires confirmation in a larger study of participants.” The 2017 Chinese study, in which 600 people were tested, was the most confident, but buried in its results the authors said: “The exact mechanism by which acute exposure to A1 casein augments gastrointestinal symptoms… is unclear.” Mostly, they suspected A1 caused inflammation, because of changes in stool softness.
The strongest claims in favor of A2 milk draw from studies performed on rats, which showed that digestion of A1 protein releases BCM-7, a natural opioid formed in the stomach upon drinking milk, which inflamed the rats' intestines. The European Food Safety Authority (EFSA) reviewed the claims about A2 milk in a 2009 study, which concluded that although digestion of A1 protein releases BCM-7 in humans too, it couldn't conclusively prove that BCM-7 caused significant symptoms. When asked to respond to the EFSA’s decision not to further research A1 and A2 milk, in the face of inconclusive causation, Waltrip says, “Instead of cherry-picking one study, it is particularly important to rely on the body of evidence that has been built over time to substantiate the digestive benefits of the A2 protein type. In the end, the response from the consumer is what matters most, and that has already been quite conclusive.”
Savaiano, the scientist at Purdue University, though, is partway through the first American study on A2 milk using human test subjects. Like the Chinese and Australian studies' authors, he too was approached by the a2 Milk Company, which is providing $120,000 in gift money to Purdue. Of 150 people who want to take part as test subjects, Savaiano is only taking individuals who have symptoms—any symptoms—from drinking milk; he ultimately expects only 25 to 30 people to qualify to become test subjects. So far only seven have been accepted, and final results are a year away.
All the studies to date have riled the National Dairy Council trade group, who like Van Amburgh, say the a2 Milk Company cherry-picks its data. Critics aren't saying there's proof that A2 milk is no good, or that A1 milk doesn't cause symptoms, but rather that any claims for or against A1 or A2 milk are based on weak evidence. But like the a2 Milk Company, the National Dairy Council is an invested party in this tug-of-war. Each is trying to sell you something, and for the NDC it's their members' vast number of Holsteins' A1-concentrated milk, by far the most popular dairy breed.
No invested party has paid me a dime, so I began buying A2 milk about the time I began writing this story. Worth a shot if you've got $5 to spare for a half-gallon, right? I've been drinking it daily for the past five weeks, and I've felt fine—I even drank a pint on a few occasions and felt all right. (Normally, after drinking a pint of regular milk, I'd be writing out my will.) “It could be a placebo,” Savaiano says when I tell him, echoing my initial thoughts upon becoming a person who buys special milk.
A2 milk is now within reach of most Americans. Boutique dairy farms and major retailers' house brands are marketing their own Jersey cow milk under the assumption that it's better for your digestive system, piggybacking on the a2 Milk Company's evangelism and research.
As for how to figure out your milk problems now that the dairy industry and scientists have talked you dizzy, you've got a few roads ahead of you, and you can take all three: You can visit a gastroenterologist to determine if you're lactose intolerant, or if you're what they call a maldigester—somebody who needs to ease into milk-drinking by starting with small amounts and progressively ramping up. You can visit an allergist to determine if you have a milk allergy, another distinct condition that means your immune system overreacts to dairy. Or you can spring $5 for a carton of A2 milk if you don't mind handing money to a company that's yet to conclusively prove its claims, and if you're aware of the placebo effect.
Skepticism, though, is going to keep plaguing A2 milk until a disinterested party performs a well-designed research study on humans that goes further than the EFSA study, and when scientists buy into its conclusions.
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