The gut microbiota plays an important role in the pathogenesis of IBD. Many factors influence the composition of the gut microbiota, including age, genetics and diet. In this presentation, Prof Wu presents an overview of the epidemiological data on the association of diet with the development of IBD. Data show that diet can influence both the form and function of the gut microbiome. Furthermore, diet can also serve as a substrate for the production of small molecules that can have profound physiological effects. As such, the interactions between diet, the gut microbiome and the metabolome present tremendous opportunity and great challenges in the management of patients with IBD. Defined formula diets (DFDs) may be an effective treatment modality for Crohn's disease. The effect of DFDs on the gut microbiome and its metabolome is being investigated so that 'better' diets can be recommended for IBD patients.