This clinical trial aims to test the psychobiological effects of certain substances produced by gut bacteria, known as short-chain fatty acids (SCFAs), in people with anorexia nervosa.

Objective This protocol proposes investigating the effects of short-chain fatty acids (SCFAs), produced by gut bacterial fermentation of dietary fiber, as mediators of microbiota-gut-brain interactions on the acute stress response, eating behavior, and nutritional state in malnourished patients with anorexia nervosa (AN). SCFAs have recently been proposed as crucial mediators of the microbiome's effects on the host. Emerging evidence suggests that SCFAs impact human physiology through various physiological pathways and may regulate stress responses and eating behavior. Method The investigators will conduct a randomized, triple-blind, placebo-controlled trial in 92 AN patients. Patients will receive either a placebo or a mixture of SCFAs (acetate propionate, butyrate) using colon-delivery capsules (CDCs) for six weeks. This clinical trial is an add-on to the standard inpatient psychotherapeutic program focusing on nutritional rehabilitation. Hypotheses The investigators hypothesize that colonic SCFAs delivery will modulate neuroendocrine, cardiovascular, and subjective responses to an acute laboratory psychosocial stress task. As secondary outcome measures, the investigators will assess alterations in restrictive eating behavior and nutritional status, as reflected by changes in body mass index (BMI). Additionally, the investigators will explore changes in microbiota composition, gastrointestinal symptoms, eating disorder psychopathology, and related comorbidities. Discussion The findings of this study can enhance our understanding of how gut microbiota-produced metabolites, particularly SCFAs, impact the stress response and eating behavior of individuals with AN. It has the potential to provide essential insights into the complex interplay between the gut, stress system, and eating behavior and facilitate new therapeutic targets for stress-related psychiatric disorders.