The goal of this observational study is to learn if behavioral and psychological factors are associated with the intestinal microbiota composition and function in children and adolescents with eating disorders (ED). The main questions it aims to answer are: * Are there any differences between the microbiota composition and function in adolescent patients with eating disorders and healthy adolescents? * Are the dietary pattern and other lifestyle habits associated with the intestinal microbiota composition in patients with a recent onset eating disorder? * Is it possible to predict the treatment response at one year by looking at any of the psychological and biological factors measured in the patients at baseline? * Are there any differences in the intestinal microbiota among patients with different subtypes of anorexia nervosa (restrictive, binge-purging, atypical) or with avoidance/restrictive food intake disorder (ARFID)? Researchers will compare the results with those obtained from a group of healthy children and adolescents matched by sex and age to find out if the associations observed differ between ED and control participants. Participants with ED will fill in different lifestyle questionnaires and psychological tests; they will also undergo anthropometrical measurements and will provide fecal and blood samples at baseline and one year later. Healthy participants will provide the same lifestyle information, anthopometrical measurements and stool and blood samples. They will only undergo the baseline evaluation.