The role of nutrition in the treatment of inflammatory bowel disease is controversial. Changing the patients diet by increasing their calorie intake, increasing the fiber, or decreasing the residue have been recommended in the treatment of Crohn's disease. Diet has been successful as primary treatment for Crohn's disease, either by total parenteral nutrition or elemental diet. How dietary therapy works is conjectural but it appears to play a fundamental role, perhaps by removing intraluminal factors that can induce or maintain inflammation. Eicospentaeoic acid competes with arachidonic acid metabolism and decreases the production of chemotactic factors and, from a small pilot study, may have a therapeutic role in the treatment of ulcerative colitis.