The Challenges of Performing Controlled Trials of Diet Therapies in Gastroenterology

Dietary trials methodology in the field of translational gastrointestinal research is fraught with constraints, relating to cost, practicalities of executing dietary trials, and the particulars of manipulating foods that often cannot be overcome. As such, dietary interventions may be unfairly judged as low quality. However, dietary trials are commonly poorly designed, based principally on drug trial methodology, which is often not appropriate in the setting of food, has a very different composition, and is not delivered like pharmaceuticals. This risks accurate interpretation of data and a lack of translatability to clinic. Careful attention should be given to the design of dietary trials to ensure studies remain high quality and clinically relevant. This review summarizes the key factors necessary for consideration when executing a well-designed dietary trial for gastrointestinal conditions and examples of how they have been used and reported on. Key factors include modeling dietary composition to meet the research question, appraising pre-exposure diets and their impact on the study, interpretation and potential use of placebo and nocebo effects, and the use of sham diets. Finally, measuring and reporting on blinding and adherence, which is essential, as for all trials methodology.