Section update. The anti-hyperglycaemic drug metformin actually increase intestinal glucose-absorption from the diet and elevate the glycolytic rate of enterocytes. This is originally a tactic devised by plants to avoid predation by herbivores. The result is an increase in energy-waste followed by activation of energy- and glucose-sparing strategies at a systemic level in diabetic patients such as decreased hepatic gluconeogenesis which in turn cause decreased glycemia. Interestingly, in healthy subjects there is instead an increase in gluconeogenesis as a response to oral metformin.
Since the drug cause an increase in glucose metabolism in diabetic patients, it shows that they can in fact burn off excess glucose, but wont, and the contrast to the response in healthy subjects seems to suggest that diabetic patients is instead trying to conserve energy. So why is this?