Published in the European Journal of Clinical Nutrition (EJCN) earlier this month, the Curtin University study identified a “significant positive association between abdominal pain” and the consumption of milk containing A1 beta-casein protein.
Dairy cows typically produce milk containing both A1 and A2 beta-casein protein. A1 beta-casein protein has previously been linked to digestive discomfort, but there is no solid evidence to support claims that milk containing just A2 beta-casein protein has a different gastrointestinal effect in humans.
The a2 Milk Company, which funded the Curtin University study, markets milk that is rich in A2 beta-casein protein but contains no A1 beta-casein protein.
Geoffrey Babidge, managing director and CEO, the a2 Milk Company, said that the Curtin University findings "further underpins" its digestion claims.
“The reported outcomes are significant in providing further insight into the digestive benefits that thousands of a2 Milk consumers experience every day,” he said.
“It further underpins our belief that more consumers can enjoy the benefits of natural dairy milk without having to resort to modified milk and non-dairy alternatives.”
The Curtin University study's 41 male and female participants first underwent a two-week dairy washout, during which time regular milk was replaced with rice milk.
Those recruited were then required to consume a daily 750ml measure of milk containing either A1 or A2 beta-casein protein for two weeks.
After a second dairy washout, the 41 participants drank the same daily measure of milk containing the alternative A2 or A2 beta-casein for two weeks.
"The A1 beta-casein milk led to significantly higher stool consistency values compared with the A2 beta-casein milk," said the study.
"There was also a significant positive association between abdominal pain and stool consistency on the A1 diet, but not the A2 diet."
“These preliminary results suggest differences in gastrointestinal responses in some adult humans consuming milk containing beta-casein of either the A1 or the A2 beta-casein type," said the Curtin University study.
The researchers added, however, larger study would be required to confirm these findings.
Debate about the gastrointestinal effect of A1 beta-casein protein is currently raging in Australia.
In March 2014, Parmalat Australia CEO Craig Garvin told the Australian Financial Review that the digestive health benefits touted by a2 milk, which now controls around 8% of the fluid milk market Down Under, were "denigrating normal milk."
Australian consumer group Choice recently jumped on the anti-a2 bandwagon, stating that there is "nothing to fear from milk that doesn't milk make apparently remarkable claim about A2."
Source: European Journal of Clinical Nutrition doi:10.1038/ejcn.2014.127
Title: Comparative effects of A1 versus A2 beta-casein on gastrointestinal measures: a blinded randomized cross-over pilot study.
Authors: S Ho, K Woodford, S Kukuljan and S Pal.