The cause of IBD is widely accepted as relating to the mucosal immune response to stimulation from the gut bacteria, on a background of genetic susceptibility. The bacteria and other organisms in the gut play a central role in the development of IBD in the West. However it is unknown if the gut bacteria differ between Chinese patients with IBD and non-IBD (healthy subjects) in Hong Kong, and whether it is affected by diet or changes in diet. A family history is the largest risk factor for the disease. More than 50 different genes associated with IBD have recently been identified in the West and preliminary data showed that Chinese patients have a different genetic profile to Western populations.