Larch Arabinogalactan Alleviates Colitis by Modulating Gut Microbiota and Promoting <i>Bacteroides thetaiotaomicron</i>

Inflammatory bowel disease (IBD) is linked to gut microbiota dysbiosis, and modulating microbiota through diet is a promising IBD management strategy. Larch arabinogalactan (AG) is a natural polysaccharide with potential prebiotic effects; however, its regulatory effects on gut microbiota and the underlying anti-inflammatory mechanisms remain unclear. Here, we demonstrated that AG improves gut homeostasis in dextran sulfate sodium-induced colitis mice, with effects depend on the gut microbiota. Further analysis revealed that AG notably enriched the <i>Bacteroides</i>, particularly <i>Bacteroides thetaiotaomicron</i>. Specifically, <i>B. thetaiotaomicron</i> exhibited anti-inflammatory activity, producing propionate and upregulating colonic G-protein-coupled receptor 41 (GPR41) expression, effects also observed in AG-treated mice. Collectively, our findings reveal the targeted regulatory effects of AG on gut microbiota and demonstrate that the <i>B. thetaiotaomicron</i>-propionate-GPR41 axis contributes to the amelioration of colitis by AG. These results provide new scientific evidence for the application of AG in health foods and offer novel insights for microbiota-targeted nutritional intervention.