Inonotus obliquus Ameliorates Metabolic Dysfunction and Attenuates Obesity by Enriching Enterococcus casseliflavus

Obesity has emerged as a growing global epidemic, substantially increasing the risk of several diseases. Inonotus obliquus (IO) is a traditional edible and medicinal mushroom known to ameliorate hyperglycemia and hyperlipidemia. However, its effects on the gut microbiota and the underlying mechanisms remain elusive. Here, we investigated the anti‐obesity effects of IO and explored gut microbiota‐mediated mechanisms using a high‐fat diet (HFD)‐induced obese mouse model. Fecal microbiota transplantation (FMT) and 16S rRNA gene sequencing were performed, followed by Enterococcus casseliflavus (EC) intervention experiments. IO administration markedly reduced HFD‐induced obesity without altering energy intake. Recipient mice that received FMT from IO‐treated donors exhibited anti‐obesity and thermogenic effects, indicating a transferable role of the gut microbiota. EC was significantly enriched following IO treatment, and EC intervention alone recapitulated the metabolic benefits of IO, including increased energy expenditure and enhanced thermogenic gene expression in both brown and white adipose tissues, accompanied by upregulation of uncoupling protein 1 (UCP1) and oxidative phosphorylation‐related proteins. Notably, EC was only transiently detectable in the gut but still improved systemic metabolic homeostasis, strengthened intestinal barrier function, reduced inflammation, and induced substantial remodeling of the serum metabolome, with elevated mesaconic acid as a key anti‐inflammatory metabolite. This study demonstrates that IO ameliorates obesity by enriching EC, which acts as a transient probiotic, highlighting EC as a potential therapeutic candidate for obesity.