Comparative Effects of A1 Versus A2 Beta-Casein on Gastrointestinal Measures: A Blinded Randomised Cross-Over Pilot Study

Eur J Clin Nutr. 2014 Sep;68(9):994-1000. doi: 10.1038/ejcn.2014.127. Epub 2014 Jul 2.

Abstract

Background/objectives: 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.

Subjects/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.

Publication types

  • Comparative Study
  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Abdominal Pain / etiology*
  • Adult
  • Aged
  • Animals
  • Caseins / pharmacology*
  • Cattle
  • Cross-Over Studies
  • Digestion / drug effects*
  • Double-Blind Method
  • Endorphins / metabolism
  • Feces
  • Female
  • Gastrointestinal Tract / drug effects*
  • Gastrointestinal Tract / metabolism
  • Humans
  • Leukocyte L1 Antigen Complex / metabolism*
  • Male
  • Middle Aged
  • Milk / chemistry*
  • Peptide Fragments / metabolism
  • Pilot Projects
  • Young Adult

Substances

  • Caseins
  • Endorphins
  • Leukocyte L1 Antigen Complex
  • Peptide Fragments
  • beta-casomorphin 7