The effect of insulin on cardiac autonomic balance predicts weight reduction after gastric bypass

Abstract

The aim of this study was to assess the predictive role of autonomic reactivity in body weight loss induced by gastric bypass. A group of 22 morbidly obese subjects, who were due to undergo a gastric bypass, were submitted, before surgery, to a euglycaemic-hyperinsulinaemic clamp, during which a continuous recording of the ECG was performed. The effect of insulin on cardiac autonomic balance was evaluated by performing power spectral analysis of heart rate variability. The low-to-high frequency ratio was calculated before and during the clamp and its modifications were expressed as % delta low-to-high frequency ratio (%Delta L: H). Preoperative %Delta L: H showed a significant (p=0.0009, r2=0.43), positive relationship to the reduction of body weight, measured 1 year after surgery and expressed as % excess weight loss (% EWL). Preoperative BMI was also significantly (p=0.0009, r2=0.43) negatively related to the 12-month % EWL. In a multiple regression analysis, %Delta L: H remained a significant (p=0.003), independent predictor of body weight loss, even when preoperative BMI or age, % fat mass, insulinaemia and glucose disposal were taken into account. The best correction of excess body weight was achieved by those obese subjects who had a preserved capacity to shift their cardiac autonomic balance towards a sympathetic prevalence in response to an euglycaemic-hyperinsulinaemic clamp. Further studies are needed to elucidate the mechanisms through which the autonomic nervous system influences weight reduction.