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20 April 2016 - FoodNavigator USA - Digestive issues attributed to lactose intolerance may be caused by A1 beta-casein protein, suggests study

by Elaine Watson

Digestive symptoms attributed to lactose intolerance might instead be caused by A1 milk protein


Many people who currently blame lactose (milk sugar) for the unpleasant digestive and other symptoms they experience when they consume standard cows' milk may instead be reacting to the A1 beta-casein protein, according to a groundbreaking new study from China.

Perceived lactose intolerance affects around 90% of the Han Chinese population, giving rise to classic GI symptoms such as bloating and digestive discomfort, and sometimes other apparent adverse 'food intolerance' reactions.

In this randomised, double-blind, placebo-controlled trial, 45 Chinese adults, 23 of whom were classified as lactose intolerant (via measures of urinary galactose) consumed either standard cows' milk (containing a mixture of A1 and A2 beta-casein) or milk containing only the A2 form of beta-casein for a 2-week period. 

When consuming milk containing A1 beta-casein, both the lactose-intolerant and the other participants experienced more GI symptoms, slower intestinal transit time, and higher scores on biomarkers of inflammation than they did when consuming milk containing only the A2 milk protein, which caused no such adverse effects.

Lactose concentrations were identical in both the A2 milk and the standard A1/A2 cows' milk, so these findings indicate that the digestive and other symptoms many people experience when consuming standard cows' milk products may not reflect lactose intolerance as such, but instead result from adverse reactions to the A1 milk protein.

Of particular interest, participants also showed poorer cognitive performance after drinking milk containing A1 beta-casein than milk with A2 protein only.  This supports other evidence linking GI symptoms with brain health, and is consistent with reports of 'brain fog' - i.e. attention and concentration problems - as another feature of apparent cows' milk intolerance that can affect some people.

For details of the associated research, see:

For more information on reported differences between A1 and A2 beta-casein, see:

New clinical research – funded by the a2 Milk Company – lends credence to its claims that many consumers who believe they can’t tolerate lactose (milk sugar) should really be blaming their digestive discomfort on the A1 beta casein protein in milk products instead. However, more human data is needed before this moves beyond the realm of theory into fact, says the National Dairy Council.

Digestive issues after drinking milk are typically attributed to milk protein allergy (which can be severe) or intolerance to lactose (milk sugars). But if both of these have been ruled out and people are still experiencing mild digestive discomfort, something else may be going on, claims the a2 Milk Company, which has developed a genetic test to identify cows that only produce A2 beta casein protein (most produce A1 and A2), so their milk can be segregated and marketed as a more ‘gut-friendly’ option.

While not everyone is convinced by the science underpinning the business (more on that HERE ), a2 milk has secured almost 10% of the fluid milk market by value in Australia, and is hoping to achieve similar success in the US market (it hit shelves in California last year and is now available in chains from Kroger and The Fresh Market to Whole Foods Market).

Doubled-blind, randomized crossover trial

A new study – published in the peer reviewed publication Nutrition Journal – tested the a2 Milk Company’s theory in a doubled-blind, randomized 2x crossover trial with 45 Chinese Han subjects with self-reported lactose intolerance (chosen because of the high rate of perceived lactose intolerance in this population).

(Of the 45 subjects, 23 were confirmed to be lactose intolerant based on the results of a urinary galactose test.)

The study - conducted at the Department of Gastroenterology, Xin Hua Hospital Affiliated to Shanghai Jiao Tong University School of Medicine in Shanghai - aimed to compare the effects of milk containing A1 & A2 beta-casein (milk containing A1 only is not commercially available and is also not representative of consumer milk products) with those of milk containing exclusively A2 beta-casein on inflammation, symptoms of post-dairy digestive discomfort, and cognitive processing.

Each treatment period was 14 days with a 14-day washout period at baseline and between treatment periods, while the consumption of dairy products other than those provided was prohibited throughout the study.

According to The a2 Milk Company, originally all domesticated cows produced milk containing only the A2 type of beta-casein. However, owing to a natural genetic mutation, another milk protein (A1 beta-casein) appeared in Europe and spread throughout global herds, such that now, most contain A1 and A2. 

The results: ‘Exacerbation of GI symptoms associated with milk in lactose intolerant subjects may be related to A1 beta-casein rather than lactose per se’

Compared with milk containing only A2 beta-casein, the consumption of milk containing both beta-casein types was associated with significantly greater post-dairy digestive discomfort symptoms; higher concentrations of inflammation-related biomarkers; longer gastrointestinal transit times and lower levels of short-chain fatty acids; and increased response time and error rate on the Subtle Cognitive Impairment Test (SCIT).