A1 β-casein and A2 β-casein: effects on the gastrointestinal motility, digestion, and absorption

This study compared A1 and A2 β-casein using a constipated mouse model and ex vivo intestinal sac assays. A2 β-casein significantly improved constipation-related outcomes—enhancing body weight recovery, shortening the first black stool time, increasing fecal water content, and accelerating small intestinal transit compared to A1 β-casein ( p < 0.05). Moreover, A2 β-casein upregulated excitatory neuropeptides (promoting motility) and downregulated inhibitory ones, while histology showed reduced colonic damage, more goblet cells, and less inflammation. Absorption assays revealed faster protein digestion uptake across all intestinal segments, particularly in the duodenum and jejunum. In conclusion, A2 β-casein outperformed A1 in relieving constipation, restoring gut function, and improving protein absorption, supporting its potential in functional dairy applications. • A2 β-casein showed better digestion than A1β-casein. • A2 β-casein improved constipation symptoms and promoted bowel motility. • A2 β-casein could effectively regulate gastrointestinal regulatory peptides. • A2 β-casein could protect colonic tissue integrity and mitigate inflammatory responses.