In individuals with type 2 diabetes, we observed that metformin (850 mg) ingested 30 min before an intraduodenal glucose infusion of 8.37 kJ/min (2 kcal/min) reduced the rate of glucose absorption by approximately 10%, and that the augmentation of GLP-1 secretion by metformin was related directly to the magnitude of inhibition of glucose absorption [9]. This evidence concerns the gene GCG and type 2 diabetes mellitus.