A2 β-casein milk improves gastrointestinal symptoms in healthy adults: A 7-week randomized, double-blind, crossover trial

Based on the potential differential effects of β-casein variants, we hypothesized that consumption of A2A2 β-casein (A2A2 β-CN) dairy would lead to improvements in gastrointestinal (GI) comfort and fecal microbiota composition than conventional milk containing A1A2 β-casein (A1A2 β-CN). This study aimed to assess the effects of consuming A2A2 β-CN dairy on GI discomfort, fecal characteristics, and emotion in different age groups of healthy individuals. Furthermore, it sought to compare the resultant fecal microbiota composition with that following consumption of conventional milk containing A1A2 β-CN, and to examine the correlation between shifts in microbial composition and changes in GI comfort parameters. A total of 70 participants (ages 25–65) were recruited and randomly assigned to two sequences: Sequence AB ( n = 34) and Sequence BA( n = 36). A 7-week randomized, double-blind, crossover trial was conducted. Comparative analysis revealed that consumption of A2A2 β-CN was associated with a greater alleviation of GI discomfort than consumption of A1A2 β-CN. Significant differences in bowel sounds, flatulence, and fecal microbiota composition were observed following A2A2 β-CN intake compared to A1A2 β-CN intake. Furthermore, our study demonstrates an association between A2A2 β-CN consumption and improvements in GI comfort and fecal microbiota composition. • A2A2 β-casein milk alleviates GI discomfort in healthy adults compared to A1A2 β-casein milk. • The beneficial effects of A2A2 β-casein were more pronounced in middle-aged and elderly groups. • Consumption of A2A2 β-casein milk significantly altered the fecal microbiota structure. • LEfSe analysis identified specific bacterial taxa that were enriched following A2A2 β-casein milk intake. • Significant links between shifts in microbiota and improvements in GI symptoms, fecal characteristics, and mood were found.