<p>Anorexia nervosa (AN) is a severe mental disorder characterized by restrictive eating and disturbance in the way one’s body weight or shape is experienced, often accompanied by depression and anxiety. Current evidence-based treatments for AN have limited efficacy, with less than half of the patients achieving full recovery in long-term follow-up studies. Recent findings have identified gut microbiota (GM) dysbiosis as a potential contributor to AN pathology through the gut-brain axis. This open-label, non-randomized, feasibility trial (Clinicaltrials.gov Identifier: NCT05834010) evaluated the feasibility of utilizing fecal microbiota transplantation (FMT) to modify the GM and GM-associated signaling in females with AN and to examine biological effects following a single FMT procedure. Adult female participants diagnosed with AN were recruited. FMT was administered either orally via capsules or as rectal enema. Stool and blood samples were collected pre- and one week post-FMT to assess GM composition, hormonal changes, and biomarkers. Primary endpoints: Feasibility of FMT in individuals with AN and preferred route of FMT. Secondary endpoints: A single FMT treatment can alter GM composition in individuals with AN short term and relevant gut brain signaling in serum. 18/22 participants (81%) completed FMT and sampling and 19/22 participants chose oral capsules, with no serious adverse effects reported. GM analysis showed significant shifts toward donor composition 1-week post-FMT, with improved stool consistency. No significant changes were observed in psychopathology measures or appetite-related biomarkers. Oral FMT is a feasible intervention for adult women with AN, leading to changes in GM profile. Future studies should focus on placebo-controlled trials to assess the efficacy of repeated oral treatments and explore long-term effects on GM, appetite, body weight, sex hormones, disorder-specific symptoms, and overall well-being</p>