Abstract: Objective To investigate the effects of metformin on insulin sensitivity and secretion in patients with obesity and insulin resistance. Methods This study enrolled the obese patients with insulin resistance who were regular followed-up in Peking Union Medical College Hospital from September 2012 to May 2016 . They were divided into two groups according to their different status of glucose metabolism: normal glucose tolerance(NGT) and impaired glucose regulation(IGR).Life style intervention and metformin were given to all these patients. The antropometric and metabolic data were collected at baseline (before treatment) , 3 months and 6 months after treatment respectively. Results: 42 patients (aged 23.6±6.5 years) including 11 males and 31 females were enrolled. 19 of them were NGT and 23 were IGR ( 8 of IGT and 15 of IFG). Among all these patients, fasting insulin was significantly higher at 3 months after therapy than the baseline（P<0.05）.The same situation were observed in Group-NGT（P<0.05）. Fasting insulin was significantly lower at 6 months after therapy than at baseline among all patients（P<0.05）. HOMA-IR showed no significant difference between the baseline and 3 months after therapy, but significantly higher at baseline and 3 months after therapy than 6 months after therapy（P <0.001）. HOMA- beta was significantly（P <0.001）lower at baseline and 6 months after therapy than 3 months after therapy among all patients. HOMA- beta was significantly lower at baseline in Group-IGR than at baseline in Group-NGT (P<0.05). Conclusions The effect of metformin on insulin secretion is earlier than that of improving the insulin sensitivity in patients with obesity and insulin resistance. Metformin is more likely to promote insulin secretion in patients with normal glucose tolerance than those with IGR within 3 months of intervention.

Key words: metformin, Insulin secretion, insulin sensitivity, Islet beta cell