Encapsulated faecal microbiota transfer in young women with anorexia nervosa: an open-label feasibility pilot trial.

Perturbations of the gut microbiome have been associated with anorexia nervosa (AN) suggesting microbiome-modulation treatments, like faecal microbiota transfer (FMT), may offer therapeutic benefits. This open-label feasibility pilot trial evaluated the tolerability and microbiological impact of encapsulated, multi-donor FMT in 18 young women with AN (Registration: ACTRN12621001504808). Participants completed clinical and microbiome assessments at enrolment (3 weeks pre-treatment), baseline, and 3, 6, and 12 weeks post-treatment. Fifteen participants completed FMT, and 11 completed the final follow-up. The primary outcome was the change in gut microbiome composition from baseline to 3 weeks compared with natural variation between enrolment and baseline. FMT produced a significantly greater shift post-treatment (mean ± SD Bray-Curtis dissimilarity 0.36 ± 0.11; p = 0.0007), with participants gaining 38 ± 16 new species. Donor-derived strains comprised 41 ± 12% of the microbiome at 3 weeks, with engraftment persisting at 6 and 12 weeks. FMT was generally well tolerated; adverse events were mostly mild to moderate and overlapped with typical AN symptomatology. Monitoring of clinical outcomes supported the safety profile and suggested potential improvements in anxiety and metabolic parameters; however, the small sample and absence of a control arm preclude safety and efficacy inference. Overall, these findings warrant further investigation through randomised controlled trials in AN.