Fresh research links traditional milk with digestive problems, but finds a new culprit.
ANSWER: The devil is in the detail – in this case a small protein that constitutes a minute proportion of cows’ milk has a sizeable impact on our gastrointestinal well-being. There’s emerging evidence that the digestive problems we’ve associated with lactose intolerance from drinking milk may in fact come from a protein in A1 milk, rather than lactose sugars. A2 milk has a variant of the protein that does not appear to cause the same discomfort among some milk drinkers.
Cows’ milk is a rich source of protein and about 80% of that protein is casein, of which 30-35% is beta-casein. Depending on the cows’ genetic profile, the beta-casein is one of a number of variants – with A1, A2 and B the most common.
The beta-casein composition of cows’ milk wasn’t a big topic until about 15 years ago, when we learnt that the majority of New Zealand dairy cows produced A1-predominant milk and that this variant (and to a lesser extent B) was implicated in a raft of chronic diseases, such as type 1 diabetes and ischaemic heart disease.
Public health specialist Boyd Swinburn produced a report for the New Zealand Food Safety Authority (NZFSA) in 2004 on the role of beta-casein in human health. Swinburn found “very suggestive evidence” from observational studies linking A1 milk to type 1 diabetes and ischaemic heart disease. But he noted that good human clinical-trial evidence was lacking and recommended more clinical research, communicating the uncertainty of the A1/A2 hypothesis to the public and that new evidence be monitored – along with claims about the purported health benefits of A2 milk.
However, the NZFSA didn’t communicate much of anything. So, when Professor Keith Woodford’s book, Devil in the Milk, was published in 2007, highlighting the possible health effects of A1 milk and the political manoeuvring that may have silenced Swinburn’s report, it set off a maelstrom of super-sized milkshake proportions.
The NZFSA’s communication – or lack thereof – to the public about Swinburn’s 2004 report was widely criticised. The 2008 Slorach Review found there had been a lack of transparency by the NZFSA.
Ultimately, the NZFSA did no further investigations into A1 milk, because the European Food Safety Authority published an in-depth review in 2009. That review concluded there wasn’t sufficient evidence to establish a relationship between A1-predominant milk and the suggested diseases.
This year, another review of A1 milk and human health was published in the journal Nutrition Reviews. It found “moderate certainty” for adverse “digestive health effects” from drinking A1 milk – namely, delayed intestinal transit times and looser stools. But there was “low or very low certainty” that any other adverse health effects were linked to A1 milk.
Similar associations for delayed intestinal transit and looser stool consistency with A1 milk were found in a 2017 review, published in Advances in Nutrition. It also associated digestive discomfort with A1 milk, but not A2.
Standard A1 milk seems to worsen symptoms we attribute to lactose intolerance (flatulence, bloating, abdominal pain, unusual stools), suggesting, perhaps, that what we’ve traditionally thought of as “lactose intolerance” may actually be caused by A1 beta-casein proteins, not lactose sugars.
If that’s the case, A2 cows’ milk could be tolerated by hundreds of thousands of current cows’ milk-avoiders globally. Which may explain, in part, why Fonterra this year entered into a strategic relationship with The a2 Milk Company. The plan is to get more Fonterra farmers to provide A2 milk and together produce and market it to meet the growing international demand.
Gut issues aside, there are no significant nutrient differences between A1 and A2 milk. They both provide energy, protein and plenty of calcium. However, A2 milk does cost more than A1 milk – but if your gut isn’t a fan of A1 milk, then the extra cost of A2 milk may be worth it.
This article was first published in the November 9, 2019 issue of the New Zealand Listener.