In this study, will investigate the effect of glutamine, an amino acid, on GLP-1, insulin and glycaemia in normal lean subjects and patients with type 2 diabetes. Preliminary data published by our group suggests that glutamine is a strong determinant of GLP-1 secretion in vitro. We will test the hypothesis that glutamine lowers post-prandial glucose levels. We will also investigate whether sitagliptin modifies this effect.