This prospective observational study investigates the development of gastrointestinal (GI) symptoms in patients with anorexia nervosa (AN) and bulimia nervosa (BN) during multi-week inpatient weight rehabilitation. The study explores how the predominant nutritional strategy-flexitarian, vegetarian, or vegan-relates to changes in GI symptoms over the course of treatment. In addition to diet, the study examines how weight gain and other clinical, psychological, and demographic factors influence the trajectory of GI symptoms. Patients complete weekly questionnaires assessing GI symptoms as part of routine care at the Eating Disorder Center of the Klinik Lüneburger Heide, Germany. Further data are drawn from standard clinical assessments, including body weight, body composition, and psychometric instruments. The primary outcome is the change in GI symptom severity (measured via the GSRS score) from admission to discharge, analyzed in relation to dietary pattern and weight development. Secondary analyses will explore symptom progression over time, group differences between AN and BN, and predictors of GI symptom improvement, including dietary intake, baseline psychological status, symptom change, weight trajectory, and treatment duration. The outcomes will be analyzed separately for AN and BN. The study aims to recruit approximately 150 patients with AN and 35-40 with BN. Inclusion requires a diagnosis of AN (any subtype) or BN, age over 12 years, clinical stability, and the ability to provide informed consent. The findings aim to inform evidence-based dietary recommendations for individuals with eating disorders who experience significant GI symptoms during nutritional rehabilitation.