INS and obesity due to melanocortin 4 receptor deficiency: Major abdominal surgery was associated with a 42% reduction in insulin sensitivity from mean(SD) M value of 37.3(11.8) μmol kg−1 fat free mass (FFM) to 21.7(7.4) μmol kg−1 FFM, but this was not influenced by obesity or preoperative carbohydrate treatment.