Metabolic flexibility after bariatric surgery-induced weight loss: does diabetes impair a proper substrates utilization?

The onset of type 2 diabetes is a critical step for the prognosis of obese patients, being crucial for disease evolution and complications development. Obese diabetic subjects generally obtain poorer outcomes in terms of weight loss as compared to non-diabetic ones after treatment. Our aim was to assess if the metabolic flexibility in substrates utilization following bariatric surgery was different in diabetic, pre-diabetic and normoglycemic obese subjects.We examined 95 consecutive morbid obese females (mean-age 44.1±11.1, BMI 44.7±7.5), undergoing laparoscopic sleeve gastrectomy (LSG), before (T0) and 12 months after (T1) bariatric surgery. Among them 61 were normoglycemic, 17 pre- diabetic and 17 diabetic. Evaluation included anthropometric parameters, blood samples collection, resting energy expenditure (REE) and body composition assessment.At T0, diabetic patients were older than normoglycemic and pre-diabetic subjects and had higher basal glucose levels (6.8±1.8 mmol/L vs 5.6±0.6 mmol/L in pre-diabetic and 5.2±0.5 mmol/L in normoglycemic respectively). The three subgroups did not differ significantly in BMI, waist circumference, REE and body composition. Percent weight loss was 30.5±10.2% in normoglycemic, 27.6±8.9% in pre-diabetic and 25.9± 6.7% in diabetic patients (p<0,05 vs normoglycemic). After weight loss, all patients showed a statistically significative decrease in REE (1760±358 kcal/die vs 1285±236 kcal/die) and no differences were found among subgroups. Respiratory quotient (RQ) tends to decrease after surgery (0.816 T0 vs 0.779 T1; p=0.22). Analyzing separately the three subgroups, a reduction in RQ was observed in normoglycemic (0.820 vs 0.781; p=0.52) and in prediabetic patients (0.821 vs 0,748; p=0,03), but not in diabetic patients (0.806 vs 0.806; p=1.00).Weight loss was associated to a metabolic shift toward an increased fat oxidation (RQ reduction) in normoglycemic and pre-diabetic patients, whereas RQ in diabetic females did not show any change. This impaired metabolic flexibility could partly explain the lower weight loss observed in diabetic patients after LSG.