Full-Fat Rice Bran Alleviates Insulin Resistance and Muscle Atrophy via Modulation of the Gut-Muscle Axis in Ovariectomized Mice Fed a High-Fat Diet

The study aims to investigate the effect of full-fat rice bran (FFRB; Tainung No. 81, Taiwan) at various doses on insulin resistance, muscle atrophy, and gut microbiome in ovariectomized (OVX) mice fed a high-fat diet (HFD). Thirty-six female ICR mice were grouped into six: young sham-operated mice fed an AIN-93M diet, OVX mice fed an AIN-93M diet, OVX mice fed a HFD, and OVX mice fed a HFD with 5%, 10%, and 20% FFRB. FFRB intervention attenuated HFD-induced weight gain and visceral fat accumulation, improved insulin resistance, and enhanced grip strength in OVX mice. Notably, 20% FFRB significantly upregulated muscle protein synthesis genes (MyoG, mTOR, eIF-4EBP1) and downregulated muscle atrophy markers (FOXO1, MuRF-1), while reducing the inflammatory cytokine IL-6. 20% FFRB also improved gut barrier integrity by upregulating colonic tight junction genes (Occludin and ZO-1) and increased the abundance of SCFAs-producing bacteria Muribaculum genus. 10% FFRB significantly downregulated FOXO1 and increased the abundance of Lachnospiraceae_UCG-001 genus. In conclusion, FFRB intervention, particularly at 20%, effectively mitigated HFD-induced insulin resistance and muscle atrophy, potentially through modulation of gut microbiota and enhancement of gut barrier function.