Digestive symptoms attributed to lactose intolerance might instead be caused by A1 milk protein
Jianquin et al 2016 - Effects of milk containing only A2 vs A1 and A2 beta casein proteins on GI physiology, symptoms of discomfort, and cognition of people with self-reported intolerance to traditional cows' milk.
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).