Original Article

European Journal of Clinical Nutrition (2014) 68, 994–1000; doi:10.1038/ejcn.2014.127; published online 2 July 2014

Protein, malnutrition and wasting diseases

Comparative effects of A1 versus A2 beta-casein on gastrointestinal measures: a blinded randomised cross-over pilot study

S Ho1, K Woodford2, S Kukuljan3 and S Pal1

  1. 1School of Public Health, Curtin Health Innovation Research Institute, Curtin University, Perth, WA, Australia
  2. 2Agricultural Management Group, Lincoln University, Christchurch, New Zealand
  3. 3A2 Dairy Products Australia Pty Ltd., Melbourne, Victoria, Australia

Correspondence: Professor S Pal, School of Public Health, Curtin Health Innovation Research Institute, Curtin University, GPO Box U1987, Perth, WA 6845, Australia. E-mail: s.pal@curtin.edu.au

Received 14 March 2014; Revised 9 May 2014; Accepted 24 May 2014
Advance online publication 2 July 2014





At present, there is debate about the gastrointestinal effects of A1-type beta-casein protein in cows’ milk compared with the progenitor A2 type. In vitro and animal studies suggest that digestion of A1 but not A2 beta-casein affects gastrointestinal motility and inflammation through the release of beta-casomorphin-7. We aimed to evaluate differences in gastrointestinal effects in a human adult population between milk containing A1 versus A2 beta-casein.



Forty-one females and males were recruited into this double-blinded, randomised 8-week cross-over study. Participants underwent a 2-week dairy washout (rice milk replaced dairy), followed by 2 weeks of milk (750ml/day) that contained beta-casein of either A1 or A2 type before undergoing a second washout followed by a final 2 weeks of the alternative A1 or A2 type milk.



The A1 beta-casein milk led to significantly higher stool consistency values (Bristol Stool Scale) compared with the A2 beta-casein milk. There was also a significant positive association between abdominal pain and stool consistency on the A1 diet (r=0.520, P=0.001), but not the A2 diet (r=−0.13, P=0.43). The difference between these two correlations (0.52 versus −0.13) was highly significant (P<0.001). Furthermore, some individuals may be susceptible to A1 beta-casein, as evidenced by higher faecal calprotectin values and associated intolerance measures.



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, but require confirmation in a larger study of participants with perceived intolerance to ordinary A1 beta-casein-containing milk.

Extra navigation