Aim: In obese patients, the diet-induced weight loss markedly improves glucose tolerance with an increase in insulin sensitivity and a partial reduction of insulin secretion. The association with metformin treatment might potentiate the effect of diet alone.
Methods: From patients admitted to our Nutritional Division for diet programme, we selected obese, non-diabetic, uncomplicated patients with age 18–65 years and body mass index 35–50 kg/m2 and studied the effects of a 6-month pharmacological treatment with either metformin (850 mg twice daily) or rosiglitazone (4 mg twice daily) on possible changes in body weight, fat mass, glucose and lipids metabolism.
Results: A significant weight loss and reduction of fat mass was demonstrated with metformin (−9.7 ± 1.8 kg and −6.6 ± 1.1 kg) and also with rosiglitazone (−11.0 ± 1.9 kg and −7.2 ± 1.8 kg), without fluid retention in either treatment group. Rosiglitazone administration induced a significant decrease in glucose concentration (4.7 ± 0.1 vs. 4.4 ± 0.1 mmol/l, p < 0.005) and insulin-circulating level (13.6 ± 1.5 vs. 8.0 ± 0.,7 μU/ml, p < 0.005), an increase in insulin sensitivity as measured by homeostatic model assessment (HOMA) of insulin sensitivity (68.9 ± 8.8 vs. 109.9 ± 10.3, p < 0.005) with a concomitant decrease in β-cell function as measured by HOMA of β-cell function (163.2 ± 16.1 vs. 127.4 ± 8.4, p < 0.005). In contrast, metformin did not produce any significant effect on blood glucose concentration, insulin level and HOMA2 indexes. No adverse events were registered with pharmacological treatments.
Conclusion: Our study shows that in severely obese, non-diabetic, hyperinsulinaemic patients undergoing a nutritional programme, rosiglitazone is more effective than metformin in producing favourable changes in fasting-based indexes of glucose metabolism, with a reduction of both insulin resistance and hyperinsulinaemia. In spite of previous studies reporting rosiglitazone-induced body weight gain, in our study the joint treatment with diet and rosiglitazone was accompanied by weight loss and fat mass reduction.