Ulcerative colitis (UC) is a chronic inflammatory bowel disease. Growing evidence demonstrates that the diet, gut microbiota and metabolites have a significant impact on UC. A high fat diet with less fiber have been linked to an increased risk of UC development. However, these complex interactions on UC are not well understood. We are performing a diet intervention study in which UC patients in remission or mildly active are sequentially given a high fat or low fat diet (4 weeks of each, 2 week wash out in between).