Dietary Supplement with Milk that Contains Different β-Caseins Influences Gut Microbiota and Serum Metabolites in Mice

The composition and metabolites of gut microbiota are shaped by dietary protein, consequently affecting host physiology, health, and diseases. This study aimed to elucidate the role of β-caseins in remodeling the composition of colon microbiota and the relationship between microbiota and serum metabolites. A total of 32 mice were randomly assigned to 4 groups and gavaged with A2, A1/A2, A1 milk, or saline for 5 wk. The supplementation of A1/A2 and A2 milk led to increased weight gain, while the A2 group exhibited an increase in goblet cell number and occludin expression in the colon. 16S ribosomal RNA gene analysis revealed differences in operational taxonomic units across groups, with Bacteroidetes and Firmicutes being predominant. Notably, A2 milk was associated with increased levels of Romboutsia and Anaerostipes compared to A1 milk. Untargeted metabolomics detected 537 and 371 metabolites in positive and negative ion modes, respectively. In the A2 group, 15 metabolites (e.g., vindoline, glycerol-3-phosphate, diphenylamine) were increased, while 13 metabolites (e.g., deoxyinosine, O-arachidonoyl ethanolamine) were decreased. Muribaculum, Ruminococcus, and Bifidobacterium genera showed significant associations with these metabolites. These findings suggest that β-casein supplementation in milk alters gut microbial ecology and metabolites, potentially impacting weight gain and colonic health positively.