Developing a core outcome set for nutrition care in adult outpatients with irritable bowel syndrome (COS-RD-IBS study)

Background and aims: Irritable bowel syndrome (IBS) is a frequent disorder thought to be caused by a disturbance of the gutebrain axis. Nutrition interventions are an essential pillar of its treatment. However, there is no consensus on which outcomes should be applied to assess the effectiveness of nutrition care in IBS. Standardized outcome sets, or "core outcome sets" (COS), have been proposed to harmonize outcomes in clinical research and practice. This project aims to develop a COS for dietitian-provided nutrition care in adults with IBS or food intolerances with intestinal symptoms, to be implemented in routine outpatient practice. Methods: A comprehensive outcomes list was developed based on quantitative and qualitative studies, COS and guidelines on IBS, and important outcomes named by participants. Health service users, dietitians, gastroenterologists, and health care decision makers rated the outcomes in two Delphi survey rounds on their importance and ranked them in a third round. Data was analyzed by panel to account for the different views and sample sizes. Results: A total of 192 participants registered for the Delphi process. The following 14 outcomes reached consensus in all panels after two rounds: perception of symptom triggering foods/nutrients, intake of trigger foods/nutrients, practicability of diet, adherence, digestive symptoms overall, abdominal pain, abdominal bloating, stool consistency, stool frequency, physical functioning related QoL, nutrition related QoL, social functioning related QoL, empowerment of self-care. Conclusions: The Delphi process yielded in a 14 outcomes COS, which exceeds what is typically considered feasible in routine nutrition care. Further work is needed to refine the COS and to identify standardized measurement tools for each outcome.