Nutritional Interventions Targeting the Gut Microbiome in MASLD: From Prebiotics and Probiotics to Postbiotics and Fecal Microbiota Transplantation.

Metabolic dysfunction-associated steatotic liver disease (MASLD) is a highly prevalent liver-centred manifestation of systemic metabolic dysfunction. The gut-liver axis provides a biologically credible therapeutic rationale because intestinal dysbiosis, impaired barrier integrity, microbial metabolites, bile acid signalling, short-chain fatty acids, and trimethylamine N-oxide may influence hepatic steatosis, inflammation, and fibrogenesis. This narrative review critically evaluates dietary patterns, prebiotics, probiotics, synbiotics, postbiotics, and fecal microbiota transplantation (FMT) as microbiome-directed strategies in MASLD. The comparative framework prioritises disease-specific human evidence, clinically meaningful endpoints, trial duration and sample size, reproducibility, safety, and feasibility. Dietary optimisation remains the most clinically grounded intervention, whereas probiotics and synbiotics show modest and heterogeneous signals on biochemical or metabolic surrogate endpoints. Prebiotics are mechanistically coherent but supported by limited liver-centred trials. Postbiotics and microbiome-mediated bioactives remain early-stage and require stricter definitional boundaries. FMT is investigational and should not be extrapolated from its established role in recurrent