Berberine (BBR) is the main active ingredient of the ancient Chinese herb medicine Coptis. The hypoglycemic effect of BBR has been demonstrated in numerous studies. Although BBR is safe and effective in the treatment of diabetes, its exact hypoglycemic mechanism is still unclear. Jin-Kui Yang found that BBR can promote GLP-1 secretion from intestinal L cells in mice in vitro and in vivo, thereby achieving the effect of lowering blood glucose, but it is still unknown whether BBR can promote incretin secretion in humans. In this study, investigators plan to examine the effect of BBR on secretion of incretin in human.