Fecal microbiota transplantation in ulcerative colitis: evidence, mechanisms, and practice considerations

Ulcerative colitis (UC) is a chronic inflammatory bowel disease strongly associated with intestinal dysbiosis, reduced microbial diversity, and disrupted microbial metabolite profiles. Fecal microbiota transplantation (FMT) aims to restore microbial homeostasis and has shown a signal of benefit for induction of remission in some trials, but results are heterogeneous and long-term maintenance efficacy remains uncertain. In this narrative review, we synthesize randomized controlled trials (RCTs), systematic reviews/meta-analyses, and recent guideline and regulatory updates on FMT in UC, and integrate mechanistic insights from microbiome and metabolomics research. Across RCTs, intensive lower-gastrointestinal regimens using pooled, multidonor material, and/or anaerobic processing have most consistently achieved modestly higher steroid-free clinical and endoscopic remission than placebo in mild-to-moderate UC (approximately 25%-32% vs 5%-10% in representative studies), whereas upper-gastrointestinal delivery or oral lyophilized formulations and highly restrictive donor selection have yielded mixed or negative results. Mechanistically, responders commonly demonstrate engraftment of short-chain fatty acid producing taxa and restoration of secondary bile acid pathways. Safety profiles in trials are generally comparable to placebo for common mild adverse events, but rare severe transmissions (e.g., multidrug-resistant Escherichia coli and SARS-CoV-2) have driven stricter donor screening and have limited routine use outside regulated programs. Current guidelines recommend against FMT for UC outside clinical trials. Future work should prioritize standardized protocols, biomarker-guided personalization, combination strategies (diet/priming), and development of defined microbial therapeutics to improve efficacy and safety.