title: Comparative effects of A1 versus A2 beta-casein on gastrointestinal measures: a blinded randomised cross-over pilot study.
abstract: OBJECTIVE
  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.
  
  
  METHODS
  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 (750 ml/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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: School of Public Health, Curtin Health Innovation Research Institute, Curtin University, Perth, WA, Australia.
authors.forename: S
authors.initials: S
authors.lastname: Ho
authors.affiliation: Agricultural Management Group, Lincoln University, Christchurch, New Zealand.
authors.forename: K
authors.initials: K
authors.lastname: Woodford
authors.affiliation: A2 Dairy Products Australia Pty Ltd., Melbourne, Victoria, Australia.
authors.forename: S
authors.initials: S
authors.lastname: Kukuljan
authors.affiliation: School of Public Health, Curtin Health Innovation Research Institute, Curtin University, Perth, WA, Australia.
authors.forename: S
authors.initials: S
authors.lastname: Pal
mesh_terms: D015746:Abdominal Pain / Q000209:etiology*; D000328:Adult; D000368:Aged; D000818:Animals; D002364:Caseins / Q000494:pharmacology*; D002417:Cattle; D018592:Cross-Over Studies; D004063:Digestion / Q000187:drug effects*; D004311:Double-Blind Method; D004723:Endorphins / Q000378:metabolism; D005243:Feces; D005260:Female; D041981:Gastrointestinal Tract / Q000187:drug effects* / Q000378:metabolism; D006801:Humans; D039841:Leukocyte L1 Antigen Complex / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D008892:Milk / Q000737:chemistry*; D010446:Peptide Fragments / Q000378:metabolism; D010865:Pilot Projects; D055815:Young Adult
chemical_list: D002364:Caseins; D004723:Endorphins; D039841:Leukocyte L1 Antigen Complex; D010446:Peptide Fragments; C041128:beta-casomorphin 7