Circadian Regulation of Gut Microbial Metabolites in Intestinal Epithelial Homeostasis

The gut microbiota produces chemically diverse metabolites whose levels fluctuate depending on the time of day, driven by bidirectional coupling between host intestinal circadian clocks and intrinsic microbial oscillators. Although short-chain fatty acids have received the most attention as microbial circadian effectors, a broad class of metabolites, including secondary bile acids, indole derivatives, and branched-chain fatty acids, engage distinct epithelial receptors and transcriptional programs through mechanisms that are, to varying degrees, subject to circadian regulation. However, the mechanisms by which these metabolite classes collectively regulate barrier integrity, mucosal immune tone, and stem cell-driven renewal, as well as the consequences of their rhythmicity loss under circadian misalignment, have not been systematically reviewed. This review constructs a mechanistic framework linking microbial metabolite rhythmicity to the circadian regulation of intestinal epithelial homeostasis and evaluates dietary and probiotic interventions that modulate this axis as chronobiotic strategies. Convergent mechanisms, unresolved questions, and translational opportunities are identified across in vitro, preclinical, and clinical evidence.