Impact of Diet and Lifestyle Modification on the Intestinal Barrier Integrity in Crohn's Disease

The goal of this prospective interventional study is to evaluate whether the targeted avoidance of a particular food that was diagnosed to be disruptive for the intestinal barrier during confocal laser endomicroscopy (CLE) contributes significantly to stabilizing the intestinal barrier and improving abdominal symptoms, quality of life and disease activity in Crohn's Disease patients with food-related symptoms. The main questions the study aims to answer are: * whether a food-induced intestinal barrier disorder in Crohn's disease patients can be detected by endoscopy using confocal laser endomicroscopy (CLE) and a causal relationship with certain foods can be established. * whether a change in diet or a targeted elimination diet can restore the defective integrity of the intestinal barrier detected by CLE. * to examine whether a targeted avoidance of a food that was identified by CLE to trigger intestinal barrier disruption leads to a relevant improvement in symptoms, quality of life and disease activity in patients with Crohn's disease. Participants will undergo a two-stage nutritional therapy concept based on a two-week inpatient integrative medicinal lifestyle modification program that comprises nutritional therapy, stress management strategies, mind-body medicine, herbal medicine and exercise: * Initially, participants learn how to employ the comprehensive lifestyle modification concept and receive nutritional training on a mostly vegetarian Mediterranean wholefood diet. * In a first stabilization phase, lasting for 3 months, participants independently apply the taught Mediterranean diet and use strategies from the comprehensive lifestyle modification program. * In a second elimination phase, lasting for another 3 months, participants additionally avoid the particular food that was identified by CLE to induce an intestinal barrier defect. Crohn's disease patients will: * initially receive a clinically indicated endoscopy with CLE and food challenge to examine whether a food-induced intestinal barrier disorder is present * return to the clinic for an optional endoscopy with CLE and food challenge after the first (stabilization) phase as well as the second (elimination) phase * answer questionnaires at study start as well as after the first and the second study phase to analyze their quality of life, the severity of their symptoms and their disease activity * give samples of blood, urine, stool and bile fluid as well as intestinal biopsies during regular inpatient sampling at study start as well as after the first and the second study phase * document their intake of food and their symptoms in an App-based diary throughout the study participation