Loss of total mass of muscles (catabolism) is a serious clinical problem in patients with active inflammatory bowel disease (IBD). The investigators have earlier shown that the liver plays an important role in this stress-catabolism by increasing the production of urea during the inflammatory process.||The purpose of this study is to examine the effect of the anti-inflammatory drugs prednisolone and infliximab on the regulation of the urea synthesis in patients with active ulcerative colitis and Crohn's disease.