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Rethinking Lactose Intolerance

Lactose intolerance is one of the most common reasons for avoiding dairy1. Commonly producing distension, bloating and gas in the small intestine, lactose intolerance is the most widely accepted types of intolerance to dairy, with an array of lactose-free products readily available at supermarkets.

This is despite the fact that human breast milk contains appreciable amounts of lactose, where it serves as the main carbohydrate source for nursing infants. It is thought that most individuals are tolerant to lactose from birth, but a small proportion go on to eventually lose the ability to produce lactase; the enzyme responsible for breaking down lactose into its substituent sugars, namely, glucose and galactose.

Drinking Milk - MrSupplement Article

Lactose intolerance has traditionally been more prevalent in certain nationalities and regions, with Africa and Asian countries thought to carry the highest rates2.

But a new study looking at lactose intolerance from a different angle has cast a big shadow over what scientists’ traditionally believe to be the root cause of digestive upset when consuming millk3.

A2 vs A1 Milk for Lactose Intolerance

Using a Chinese Han population (due to their very high rate of perceived lactose intolerance), researchers from Shanghai performed a double-blind, randomised, controlled 2 x 2 cross-over study to test the comparative effects of normal milk versus A2 milk.

In contrast to normal milk, A2 milk only contains A2 beta-casein protein rather than a mixture of A1 and A2 beta-casein proteins4. When digested, A1 beta-casein produces a peptide called beta-casomorphin-7 or BCM-74. In contrast, this peptide is not produced during digestion of A2 beta-casein. As shown below, these different responses boil down to a simple single amino acid substitution at the 67th residue of the 209-amino acid beta-casein protein chain5.

A1 casein vs A2 casein structure


Which Cows Produce A2 Beta-Casein?

Interestingly, thousands of years ago, all breeds of cows only produced the A2 variant of beta-casein, until a mutation caused the appearance of A1 beta-casein in some European herds some 5000–10,000 years ago6.What’s more human breast milk only contains the A2 beta-casein variant7. Nowadays, A1 is most frequent in Holstein-Friesian, Ayrshire and Red cattle8. In contrast, a high frequency of A2 is observed in Guernsey and Jersey cattle8. Normal western milk actually contains a roughly equal portion of A1:A2 b-caseins, so it’s not as though normal milk exclusively contains A1 beta-casein. This explains why many milk brands now display “naturally contains A2 protein” on their label.

Beta-Casomorphin-7 (BCM-7)

BCM-7 as its name suggests is a seven chain amino acid peptide that is actually classified as an opioid. In a nutshell, this means it can bind to opioid receptors in the body3. Studies have shown exposure to BCM-7 can result in exerts a range of proinflammatory effects and disruption of digestive process, which may manifest as symptoms of lactose intolerance in terms of its presentation3.

As such, the authors of this latest study theorised that intolerance to dairy products in some cases may be related to the consumption of A1 beta-casein rather than lactose per se.

The study was set up in two phases, with each phase consisting of two separate arms. In the first phase, Arm 1 contained subjects that were fed normal A1/A2 milk, while in Arm 2 subjects were only fed A2 milk. This was followed by a 2 week wash out phase, after which subjects changed Arms so that if they received A1/A2 milk initially, they then received A2 milk only and vice versa.

The authors measured a range of advanced gastrointestinal healthy measures which included markers of inflammation, gut transit time, gut symptoms and levels of short chain fatty acids (a marker of gut health).  

In a nutshell, when subjects consumed the milk containing A1 beta-casein they experienced more gut inflammation, worsening of gut symptoms, delayed transit and decreased cognitive processing speed and accuracy. These negative effects were eliminated when the subjects consumed A2 only milk.

What are the implications of these findings you might ask? Well, this is the only study to date to explore the relationship between lactose intolerance and A2 milk, so we will really need further studies in different populations before one can make definitive conclusions. However for existing lactose intolerant individuals, it may be worth trialling a bottle of A2 milk, which is readily available in Australia.

Lactose Intolerance & Protein Supplements

The other interesting take away from this research is that lactose intolerant sufferers may find they can tolerate many whey proteins, despite their lactose content. This is because whey protein strictly by definition should not contain any beta-casein, thus excluding the possibility that BCM-7 could be generated upon ingestion. There are a lot of protein supplements that contain a blend of both whey and casein, which would obviously not be suitable. However, sticking with a reputable brand of whey protein should ensure it doesn’t contain any traces of milk or casein protein. Moreover,



  1. Brussow H. Nutrition, population growth and disease: a short history of lactose. Environ Microbiol. 2013;15:2154–61.
  2. Yang J, Deng Y, Chu H, Cong Y, Zhao J, Pohl D, et al. Prevalence and presentation of lactose intolerance and effects on dairy product intake in healthy subjects and patients with irritable bowel syndrome. Clin Gastroenterol Hepatol. 2013;11:262–8.e1.
  3. Jianqin S, et al. Effects of milk containing only A2 beta casein versus milk containing both A1 and A2 beta casein proteins on gastrointestinal physiology, symptoms of discomfort, and cognitive behaviour of people with self-reported intolerance to traditional cows’ milk. Nutrition Journal. 2016;15:35.
  4. Caroli AM, et al. Detecting β-Casein variation in bovine milk. Molecules. 2016;21:141;1-7.
  5. Pal S, et al. Milk intolerance, beta-casein and lactose. Nutrients. 2015;7(9):7285–7297.
  6. Ng-Kwai-Hang, K.F.; Grosclaude, F. Genetic polymorphism of milk proteins. In Advanced Dairy Chemistry: Volume 1: Proteins, Parts A & B; Fox, P.F., McSweeney, P.L.H., Eds.; Kluwer Academic/Plenum Publishers: New York, NY, USA, 2002; pp. 739–816.
  7. Hamosh, M.; Hong, H.; Hamosh, P. Beta-Casomorphins: Milk-β-casein derived opioid peptides. In Textbook of Gastroenterology and Nutrition in Infancy, 2nd ed.; Lebenthal, E., Ed.; Raven Press: New York, NY, USA, 1989; pp. 143–150.
  8. Kamiński S, et al. Polymorphism of bovine beta-casein and its potential effect on human health. J Appl Genet. 2007;48(3):189-98.
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