Insulin resistance in the severely obese and links with metabolic co-morbidities

Background: The association between insulin resistance (IR) and obesity and its causal relationship with type 2 diabetes is well recognized. The possibility of an association, causal or otherwise, with other obesity-related co-morbidities warrants consideration. Methods: IR was calculated pre-operatively in 80 patients undergoing gastric bypass surgery for severe obesity, using the homeostasis model assessment (HOMA) method, and again in 70 patients on at least one occasion post-operatively within 12 months. Correlations with weight parameters and pre-existing co-morbidities including diabetes, hypertension, dyslipidemia and hepatic steatosis were made. Results: 78/80 patients had IR pre-operatively which did not correlate with pre-operative weight or BMI. As expected, there were positive correlations between pre-operative IR and abnormal glucose tolerance and diabetes. A positive correlation was also found between IR and hepatic steatosis, but no correlation was noted between IR and hypertension or fasting levels of cholesterol, triglycerides or Choi/HDL cholesterol ratios. Improvement in IR was uniformly seen after gastric bypass, sooner than would be accounted for by weight loss alone. The degree of pre-operative IR was not a predictor of weight loss after gastric bypass in these patients. Conclusions: While IR is an almost universal accompaniment of severe obesity, it does not correlate with the degree of obesity in this group of patients. A number of important co-morbidities show a clear association with IR, and improvement in these after gastric bypass may well be related to striking and rapid changes in IR.