Microbiome-mediated crosstalk between T2DM and MASLD: a translational review focused on function.

Type 2 diabetes mellitus (T2DM) and metabolic dysfunction-associated steatotic liver disease (MASLD) frequently co-occur and aggravate one another through shared pathways of insulin resistance, low-grade inflammation and disordered lipid handling. Framing their interaction through the gut-liver-pancreas axis, this review synthesizes recent progress with a function-first emphasis, moving beyond taxonomic lists to the microbial outputs most consistently linked to dual metabolic-hepatic endpoints. We summarize how short-chain fatty acids (SCFAs), bile acids (BAs), lipopolysaccharide (LPS) and other microbe-associated molecular patterns, branched-chain amino-acid (BCAA) catabolites, trimethylamine N-oxide (TMAO) and endogenous ethanol reach the liver via portal inflow or the enterohepatic BA cycle and act on epithelial, immune and endocrine interfaces, including the farnesoid X receptor (FXR), G-protein-coupled BA receptor 1 (TGR5) and fibroblast growth factor 19/15 signaling. Mechanistic routes-barrier dysfunction and endotoxaemia; SCFA signaling with effects on enteroendocrine tone and substrate flux; BA remodeling that resets hepatic and pancreatic set-points; and nitrogen/choline and ethanol pathways that promote lipotoxic injury-offer biologically coherent explanations for parallel trajectories of hyperglycemia and steatosis/inflammation. We appraise therapeutic modulation spanning diet and fermentable substrates, live biotherapeutics/postbiotics, BA-targeting drugs, fecal microbiota transplantation and metabolic/bariatric surgery, and we outline clinically actionable biomarker opportunities using function-based panels (fermentative capacity, BA transformation, inflammatory ligands, nitrogen/methyl flux) integrated with host metabolites and genetics for diagnosis, risk stratification and response prediction. By advocating standardized reporting, careful control of diet/medications and composite metabolic-hepatic endpoints in prospective trials, this review provides a practical framework to accelerate translation from association to targeted prevention and therapy that improves glycemic control and MASLD activity in parallel.