Faecal Microbiota Transplantation in Anorexia Nervosa: A Systematic Review of Methodologies, Outcomes, and Challenges With Recommendations for Future Studies.

OBJECTIVE: Anorexia nervosa (AN) is a severe psychiatric disorder displaying an altered gut microbiome. Faecal microbiome transplantation (FMT) has emerged as a powerful research tool and potential treatment option in AN due to the microbiome-gut-brain axis. Current studies are limited and reveal variable FMT protocols. This leads to heterogeneous outcomes and complicates drawing definitive conclusions from existing literature. This review aims to compile and assess the different protocols and develop recommendations on ideal donors, handling of faeces, recipients, duration/frequency of FMT, and measuring transfer success for future FMT studies regarding AN.

METHODS: We systematically screened three databases (Pubmed, Embase, Web of Science), identifying 13 studies, including two human case reports, one human study protocol, and 10 animal studies.

RESULTS: While all studies demonstrated microbial alterations in the recipients, not all animal studies successfully induced an AN/underweight phenotype, suggesting that precise coordination of study protocol components to allow further refinement is essential.

CONCLUSION: Researchers should prioritise clear, comprehensive, and transparent documentation to ensure the interpretability and reproducibility of FMT procedures. Detailed reporting will enable more meaningful comparisons across studies, deepen our understanding of the microbiome's role in AN, and help identify methodological factors that influence outcomes. Ultimately, completeness of documentation in FMT studies in AN has substantial potential to support future clinical applications and improve patient care.