 The current study explores the incretin effect; a central mechanism of sugar metabolism. People with type 2 diabetes have a markedly reduced incretin effect, while the incretin effect never has been studied in patients with severe chronic renal failure. Non-diabetic patients with severe kidney failure and patients with diabetes and normal kidney function share several pathophysiological traits, including decreased sensitivity to insulin, fasting hyperinsulinaemia and impaired beta cell function. The investigators expect the incretin effect to be affected in patients with chronic renal failure without diabetes, which in time can result in therapeutic changes in this group of patients. 