Twenty-four hour energy expenditure and skeletal muscle gene expression changes after bariatric surgery

Obesity is characterized by decreased insulin-stimulated glucose uptake in muscle and shift from glucose to lipid oxidation, the so-called metabolic inflexibility. Biliopancreatic diversion (BPD), a mainly malabsorptive bariatric operation, determines a prompt improvement of insulin resistance, but the mechanisms are still unclear.

We aimed to estimate the response of glucose transporter 4 (GLUT4) and hexokinase-II (HKII) gene expression to hyperinsulinemia before and after surgical treatment with a BPD or dietary-induced weight loss. The association with 24-hour energy expenditure and its different components-diet-induced thermogenesis (DIT), resting energy expenditure, physical activity (PA) of daily living, and physical exercise-was also determined. DESIGN, SETTING, AND MAIN OUTCOME MEASURES: Case-control study: 20 subjects, BPD vs diet-induced weight loss. Four subjects withdrew in the surgical arm and 1 subject withdrew in the dietary arm. Insulin sensitivity was measured by the euglycemic-hyperinsulinemic clamp. Energy expenditure was assessed by indirect calorimetry over 24 hours. Muscle biopsies were obtained during the clamp to measure gene expression: GLUT4 and HKII.

Insulin sensitivity increased significantly (P < .01) only after BPD (0.101 ± 0.012 to 0.204 ± 0.033 μmol/kg/min/pM). Enhanced GLUT4 and HKII mRNA levels were observed after surgery (P < .0001 and P = .021, respectively), whereas they were not affected by diet-induced weight loss. Carbohydrate oxidation (P = .0027), DIT (P = .033), PA (P = .036), and energy expenditure during the exercise (P = .017) increased only in the BPD group.

BPD improved impaired glucose metabolism and insulin resistance through increased glucose uptake, glycogen synthesis, and glucose oxidation. Furthermore, the concomitant increase in DIT, PA, and exercise in BPD patients may partly explain their ability to sustained long-term weight loss and may contribute to the improved insulin sensitivity.