Shenling Baizhu Powder Modulates Gut Microbiota and Bile Acid Signaling to Alleviate Diet-Induced Diarrhea

Background: Shenling Baizhu Powder (SLBZP) is a traditional Chinese medicine formula used to treat diarrhea. This study investigated its therapeutic effects and potential mechanisms in mice with fatigue- and high-fat diet-induced diarrhea, focusing on gut microbiota, bile acid metabolism, and farnesoid X receptor (FXR)-related signaling. Methods: Male Kunming mice were used to establish a model of diarrhea, followed by treatment with SLBZP. Fecal moisture content, serum levels of diamine oxidase and liver enzymes, and intestinal and hepatic histopathological changes were assessed. Small-intestinal microbiota composition, bile acid profiles in colonic contents, and FXR-related signaling in the ileum and liver were further analyzed. Results: SLBZP significantly reduced fecal moisture content. It also modulated the small-intestinal microbiota, with a significant increase in Faecalibaculum. In colonic contents, SLBZP reduced total bile acid levels, increased the secondary-to-primary bile acid ratio, and altered multiple bile acid species. These changes were accompanied by increased ileal FXR expression and changes in downstream regulators involved in hepatic bile acid synthesis. Correlation analysis further showed associations of selected bacterial taxa and FXR protein expression with colonic bile acid profiles. Conclusions: SLBZP alleviates diarrhea induced by fatigue combined with a high-fat diet in mice. Its effects may involve coordinated modulation of the gut microbiota, bile acid homeostasis, and FXR-related signaling, providing experimental support for the pharmacological basis of this traditional formula in diet-related diarrhea.