There is increasing evidence that the human gut microbiota may be an important factor in the pathogenesis of various diseases, including inflammatory bowel disease (IBD), colon cancer and atherosclerosis. Many factors help determine the composition of the gut microbiota. Age, genetics and diet are key determinants of the gut microbiota. In this presentation Wu used IBD to illustrate key concepts in which the gut microbiota may be related to health and disease. Genetics, immune-regulatory defects and the gut microbiota (environmental trigger) all play a role in the pathogenesis of IBD. Dysbiosis and diet may be important to the development of disease. Wu also presented a controlled human diet study that was conducted to investigate the effect of diet on the gut microbiota. Results of this study suggest that dietary manipulation of the gut microbiota may well help maintain health and treat disease.