Gut microbiota and their metabolites are known to influence the pathogenesis and progression of metabolic dysfunction-associated steatotic liver disease (MASLD). In this study, we investigated the potential beneficial effects of <i>Phocaeicola dorei</i> in modulating MASLD progression, beginning with clinical observations and followed by mechanistic validation in animal models. Human data (49 healthy controls and 129 MASLD patients) were collected to investigate gut microbial biomarkers. The relative abundance of <i>P. dorei</i> was found to significantly vary with MASLD severity in human. Western diet-induced MASLD mice supplemented <i>with P. dorei</i> (12 weeks, 10⁹ CFU/g twice/week) or 100 μl of <i>P. dorei</i> cell-free supernatant (CFS, 5 times/week) were utilized. STAM^TM mice (10 weeks, 10⁸ CFU/g four times/week) and RAW 264.7 cells were used for the validation. MASLD severity was determined based on liver/body weight, pathology, and biochemistry markers. Cecum feces were collected for 16S rRNA gene sequencing and metabolite profiles. In the animal model, <i>P. dorei</i> oral administration and its CFS alleviated lipid accumulation by increasing β-oxidation gene expression and inhibited inflammatory response from fatty liver to hepatitis progression. In the STAM^TM model, <i>P. dorei</i> decreased nuclear atypia and cell proliferation. Additionally, <i>P. dorei</i> CFS inhibited TNF-α and CXCL10 in activated macrophages, and this result was consistent with the results of animal models. <i>P. dorei</i> and its metabolites ameliorate MASLD progression by modulating bile acid, lipid accumulation, inflammation, and proliferation. <i>P. dorei</i> could be a promising candidate for novel microbiota-based therapeutic strategies against MASLD.

Ingestion of Lactobacillus, such as L. acidophilus, L. fermentum, and L. plantarum, ameliorates the progression of nonalcoholic steatosis by lowering cholesterol. The use of Lactobacillus can be considered as a useful strategy for the treatment of NAFLD.