Discovering New Insights Into Anorexia Nervosa: Influence of MicrObial DysbiosiS (DIAMOnDS) (DIAMOnDS)

This study will investigate the link between the gut microbiota, the occurrence of the central adiposity phenotype, and the patients' fear to regain weight in anorexia nervosa.

Excessive concerns about body shape and intense fear of becoming fat are among the core features of anorexia nervosa. During refeeding, patients commonly report a disproportionate deposition of fat in the abdomen which could represent an obstacle for weight gain. It is not known whether these complaints are caused by dysmorphophobia or if the distribution of fat during refeeding could really not be uniform. Indeed, a "central adiposity phenotype" has already been objectified by anthropometric measures or imaging, with a higher proportion of visceral fat accumulated in the abdomen during the refeeding. This phenomenon could exacerbate body shape concerns and ultimately lead to an elevated risk of resistance to treatment and/or relapse. The present research project aims to explore the mechanisms that underlie these difficulties, especially by investigating the link between the gut microbiota (both composition and products) and the occurrence of the central adiposity phenotype, and the patients' fear to regain weight. Patients with severe to extreme anorexia nervosa admitted at hospital for refeeding will be included. . Stool and blood samples will be collected during the first week of admission and at discharge in order to investigate gut microbiota and metabolites. Anthromopetric data will be collected every week during hospitalisation. Dual-energy X-ray absorptiometry will be administrated at admission and discharge in order to investigate fat distribution and "central adiposity phenotype". This will allow to compare gut microbiota and metabolites between patients with and without occurence of the central adiposity phenotype during refeeding. (The definition of the central adiposity phenotype will be characterised quantitatively through repeated measures of anthropometric data throughout the hospitalisation (waist-hip ratio (WHR), triceps skin fold, body mass index (BMI) and percentage from target weight) and qualitatively through Dual-energy X-ray Absorptiometry (DXA) imaging (repartition in body segment, relative proportion of lean and fat tissues, of subcutaneous and visceral fat mass, and of android and gynoid fat mass)).

Species-level taxonomic profile and functional potential of the gut microbiota generated by shotgun metagenomics performed on stool samples collected at inclusion, between those who express or not the central adiposity phenotype.

α-diversity, β-diversity, richness in genes, richness in species and enterotype of the gut microbiota generated by shotgun metagenomics performed on stool samples collected at inclusion, between those who express or not the central adiposity phenotype

Levels of Short Chain Fatty Acids (SCFAs) (acetate, propionate, butyrate, valerate, isobutyrate and isovalerate) produced by the gut microbiota estimated through gas chromatography-mass spectrometry on blood and stool samples collected at inclusion, between those who express or not the central adiposity phenotype.

Proportion of patients who respond to the definition of the central adiposity phenotype during the refeeding. (The definition of the central adiposity phenotype will be characterised quantitatively through repeated measures of anthropometric data throughout the hospitalisation (waist-hip ratio (WHR), triceps skin fold, body mass index (BMI) and percentage from target weight) and qualitatively through Dual-energy X-ray Absorptiometry (DXA) imaging (repartition in body segment, relative proportion of lean and fat tissues, of subcutaneous and visceral fat mass, and of android and gynoid fat mass)).

Species-level taxonomic profile and functional potential of the gut microbiota generated by shotgun metagenomics performed on stool samples collected at discharge.

α-diversity, β-diversity, richness in genes, richness in species and enterotype of the gut microbiota generated by shotgun metagenomics performed on stool samples collected at discharge.

Levels of Short Chain Fatty Acids (SCFAs) (acetate, propionate, butyrate, valerate, isobutyrate and isovalerate) produced by the gut microbiota estimated through gas chromatography-mass spectrometry on blood and stool samples collected at discharge.

Women only, due to the high influence of sex hormones and the low sex ratio of men admitted at hospital for anorexia nervosa.

Inclusion Criteria: Women Over 15 years old and 3 months. Admitted in the specialized department for eating disorders of CHU Nantes for refeeding. With a diagnosis of anorexia nervosa at admission (restrictive or Binge-Eating-Purging type). Body Mass Index at admission below 16 kilogram per square meter. Written informed consent for patients over 18 years old/ oral informed consent from both the patient and a legal representative for patients under 18 years old. Affiliated with French social security system or beneficiary from such system. Exclusion Criteria: Pregnant and breastfeeding women. Who received a treatment with antibiotic/antifungal (other than local application) in the last three months. Who had a weight gain in the last month (5% or more of the patient's weight at admission). Under trusteeship or guardianship. Not fluent in French Who participate in another interventional study involving medication. Patients for whom stool collection or body mass composition analysis (with Dual-energy X-ray absorptiometry) couldn't be done during the first week of hospitalisation.