Severe insulin resistance in muscle and liver is the common defect in obesity and type 2 diabetes and may be improved or even reversed shortly after the operation. The aim of this study is to examine the acute changes in insulin sensitivity of muscle and liver by using hyperinsulinaemic euglycaemic clamp combined with glucose tracer to assess hepatic glucose production. Insulin signaling pathways will be studied in biopsies from muscle and subcutaneous fat as to explain the molecular basis of the changes in insulin sensitivity after RYGB.