Fecal microbiota transplantation in liver diseases: Therapeutic potential and associated risks.

Fecal microbiota transplantation (FMT) is a biologically coherent strategy to modulate the gut-liver axis by restoring ecosystem structure and function. This chapter synthesizes current evidence and practice of FMT in various liver disease conditions. In cirrhosis with recurrent hepatic encephalopathy (HE), randomized trials demonstrate adjunctive benefits of FMT, reducing recurrence and hospitalizations as well as improving cognition, with route flexibility (lower-GI infusions or oral capsules) and emerging microbiome predictors of response. In severe alcohol-associated hepatitis and ACLF, early single-center trials suggest fewer infections and short-term survival gains, warranting confirmation in multicenter, blinded studies for further outcomes. For MASLD/MASH, FMT consistently shifts intestinal permeability, bile-acid signatures, and hepatic transcriptomics, although it has not reliably improved MRI-PDFF or insulin resistance in unselected cohorts; future success likely requires phenotype enrichment and function-matched donors or defined consortia. Data in chronic hepatitis B remain exploratory, positioning FMT, if at all, as an adjunct to antivirals. Methods are standardized around rigorous donor screening, controlled manufacturing, indication-specific endpoints, and strain-resolved engraftment analytics linking mechanism to outcome. Refractory Clostridium difficile is the only FDA-approved indication of FMT. Use of FMT in hepatology use should remain protocolled and regulated. Priorities include precision donor matching, next-generation consortia, platform trials, and long-term safety registries.