Energy-protein malnutrition and the sub-clinical deficiencies of vitamins and trace elements, are frequent findings in ulcerative colitis and Crohn's disease, and these may negatively influence the clinical course of these diseases. In general, the majority of the patients with ulcerative colitis and uncomplicated Crohn's disease can ingest a normal diet that is well balanced and without any restrictions. The intolerance to specific foods is rare in Crohn's disease and the application of exclusion diets in a routine manner is not indicated. When the nutritional status cannot be adequately maintained with normal ingestion, the use of artificial nutrition is indicated. Enteral nutrition is the first choice nutritional support system if the gastrointestinal tract is accessible and at least partially functional. In Crohn's disease enteral nutrition could have a specific anti-inflammatory effect ("primary treatment"), and it has been suggested that this could be effective to induce the clinical remission of the activity bouts of the disease. Some types of dietary fiber could be effective in the treatment of ulcerative colitis. Initial studies suggest their usefulness in maintaining the remission of the disease.