As a continuation of a question of most adults being lactose intolerant, the marketing of The a2 Milk Company in Australia House at SxSW 2018 suggested it may not be lactose-intolerance, after all, but instead the sensitivity to the A1 protein found in cow's milk prevalent within certain countries that's causing the milk-drinking discomfort issues.

Looking for milk for Lactose Intolerance? Did you know that some people who experience lactose intolerance symptoms might actually be sensitive to A1 protein?

Lactose intolerance fact or fiction?

Many people, even trained healthcare professionals, assume if they have discomfort after drinking milk that they’re lactose intolerant without being tested to make sure. But research suggests that only about 5-7% of these cases can be attributed to Lactose Intolerance!

Is this really true?! Only 5-7% of lactose intolerance diagnoses are correct?! This would appear to be a very disruptive phenomenon on misclassification of the vast majority of the population, yet Wikipedia articles on Lactose intolerance and A2 milk, for example, make no mention of any of this, and instead the latter article goes into lengths of how The a2 Milk Company has unsuccessfully tried to lobby various governments for warning labels for non-A2-milk around unrelated and unproven long-term health effects of A1 vs. A2 milk.

Moreover, as a followup question, if it's really true that we're all not lactose-intolerant, after all, then where's the rationale for the lactase enzyme supplements and LACTAID® milk seemingly addressing the associated discomfort issues of the generic milk?!

  • See other questions on A1/A2 such as skeptics.stackexchange.com/questions/30847/…
    – GEdgar
    Jul 17, 2018 at 0:16
  • @GEdgar, those other questions are about long-term health effects without a clear relationship to immediate discomfort and flatology.
    – cnst
    Jul 17, 2018 at 0:30
  • 2
    "Is this really true?! Only 5-7% of lactose intolerance diagnoses are correct?!" You misrepresented/misinterpreted the statement. It's only a small percentage of people who self-diagnose as lactose intolerant that really are. It says nothing about people diagnosed as such by medical professionals using standardised allergy testing. Furthermore, given that the article is published on a website trying to sell you a product, I'd be rather skeptical about its findings.
    – jwenting
    Jul 17, 2018 at 5:13
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    @jwenting, your "some" would make sense if it wasn't for 75% of population being lactose-intolerant as per prior studies in my prior question, and surely the diagnosis is by the medical professionals performing the studies. When put together, these claims on A2 are really hard to put together with the prior knowledge.
    – cnst
    Jul 18, 2018 at 0:16
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    @jwenting That's incorrect. Even among Caucasians, adult lactose intolerance is extremely widespread. It just doesn't manifest as an absolute intolerance but rather as a (severely) reduced lactase activity. The symptoms are the same though, just off varying severity. Jul 19, 2018 at 7:36

1 Answer 1



The estimation of prevalence of lactose intolerance may be too high because of:

  • surveys in which they included individuals with self-diagnosed and not just officially diagnozed lactose intolerance
  • false positive diagnostic tests (up to 20% according to American Family Physician) due to other problems, such as irritable bowel syndrome, sensitivity to A1 milk protein, etc.

So, lactose intolerance may be wrongly diagnosed in 20% of cases, but not likely in "most" cases and even those 20% are from a variety of problems, not just from sensitivity to A1 milk protein.

The geographical distribution of lactose intolerance and A2 (A1-free) milk

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Image: Geographical distribution of lactose intolerance (source: New Scientist, 2015)

The distribution of A1 and A2 milk are from Today's Dietitian, 2017:

According to the California Dairy Research Foundation, the typical dairy cow in the United States produces approximately equal amounts of A1 and A2 forms of beta-casein in its milk. Dairy herds in much of Asia and Africa and parts of Southern Europe are naturally more likely to produce only A2 proteins.

So, in the areas with cows with A1-free (A2-only) milk (Asia, Africa, South Europe), the estimated prevalence of lactose intolerance is high, which does NOT support the hypothesis that it is sensitivity to A1 milk that causes gastrointestinal problems in most individuals diagnosed with lactose intolerance.

A1 vs A2 milk and gastrointestinal symptoms

In few studies reviwed here Systematic Review of the Gastrointestinal Effects of A1 Compared with A2 β-Casein (Advences in Nutrition, 2017), consumption of A1 milk was associated with gastrointestinal symptoms in some individuals, but the prevalence of the problem is not known:

In humans, there is evidence from a limited number of studies that A1 consumption is also associated with delayed intestinal transit (1 clinical study) and looser stool consistency (2 clinical studies). In addition, digestive discomfort is correlated with inflammatory markers in humans for A1 but not A2. Further research is required in humans to investigate the digestive function effects of A1 relative to A2 in different populations and dietary settings.

Lactose intolerance

In people with lactose intolerance, lactose is not fully digested due to lack of the enzyme lactase in the small intestinal lining. The undigested lactose is ultimately fermented by normal large intestinal bacteria, which produce gas and thus cause bloating and flatulence.

Hydrogen breath test for lactose intolerance:

The diagnosis of lactose intolerance is made by a hydrogen breath test in which you drink 25-50 grams of lactose in water solution (to compare: ~50 g lactose is in 1 liter of milk) and if you can't digest lactose, it will be fermented by intestinal bacteria, which will produce hydrogen, which will be absorbed into the blood and appear in your breath (intestinal bacteria are the only source of hydrogen that appears in breath). However, the test does not confirm the actual lack of the enzyme lactase, so it can be positive in other conditions with malabsorption and increased intestinal motility, in which lactose travels fast through the intestine and does not have time to be digested, for example, due to psychological expectation of intolerance, irritable bowel syndrome, small intestinal bacterial overgrowth, fructose malabsorption, celiac disease, Crohn's disease, etc (American Family Physician, 2002, Monash University, 2018). This means, it's likely that lactose intolerance is overdiagnosed, but we can't say by how much.

Individuals who are positive after a 25 g lactose test are said to be "high-grade malabsorbers." Anyway, in one 2008 study, only 16 out of 90 adults diagnosed as high-grade malabsorbers were positive after the test using 12.5 g lactose (which can be found in 1 cup or 244 g of milk).

Lactose intolerance prevalence:

Science Daily, 2009:

Previous studies have found lactose maldigestion, or low lactase activity in the gut, to occur in approximately 15 percent of European Americans, 50 percent of Mexican Americans and 80 percent of African Americans.

Nutrition Today, 2009:

However, lactose-intolerance prevalence rates in practical life settings may be lower than originally suggested. The goal of this study was to determine the prevalence of self-reported lactose intolerance among a national sample of European American (EA), African American (AA), and Hispanic American (HA) adults. Interviews were completed by a total of 1,084 respondents between the ages of 19 and 70 years with 486 EAs, 355 AAs, and 243 HAs. The age-adjusted lactose-intolerance prevalence estimates were 7.72%, 19.50%, and 10.05% for EAs, AAs, and HAs, respectively. For all respondents in the sample, the crude and age-adjusted self-reported lactose-intolerance prevalence rates were 13.38% and 12.04%, respectively.

So, the old vs new 2009 estimation of lactose intolerance prevalence in Americans is:

  • All Americans: 15-30% vs 13%
  • European Americans: 15% vs 8%
  • African Americans: 80% vs 20%
  • Mexican (Hispanic) Americans: 50% vs 12%


High estimates of lactose intolerance prevalence my be due to:

  • Large amounts of lactose used in hydrogen breath tests (up to 50 g, which is equivalent of 1 liter of milk)
  • False-positive test results due to:
    • personal differences in how fast lactose travels through the gut
    • other problems, like iritable bowel syndrome (but not mainly due to sensitivity to A1 milk) or wrongly self-diagnosed lactose intolerance

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