Approximately one third of protein in cows milk is beta -casein which is comprised of both A1 and A2 beta casein. These have different outcomes upon digestion when compared to one another due to a slight difference in the amino acid sequence on the peptide chain. A1 beta-casein preferentially releases the opioid peptide beta-casomorphin 7 (BCM-7) on digestion. In contrast, the structure of A2 limits the release of BCM-7 on digestion.
An infographic providing an overview of the A1 and A2 beta-casein protein variants. The graphic displays how upon consumption of regular milk which contains A1 beta-casein protein, BCM-7 is released resulting in gastrointestinal differences.