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

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.

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.

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 Chol/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.

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.