In summary, each individual will have three tracer studies: an initial study at baseline; a second after eight weeks of metformin; and a final tracer study after eight weeks of the TZD, pioglitazone. Tracer studies involve a standardised meal the night before the study, and fasting from midnight in preparation. No alcohol should be consumed for 24 hours before the study. On the day of the tracer study two cannulae will be inserted, one in each forearm. One cannula will be used to infuse a stable glucose tracer [6,6-2H2] for the duration of the eight hour study. After two hours of this infusion, the participant will be fed a mixed meal containing [U-13C] glucose (stable). The participant is observed for a further six hours, while the [6,6-2H2] glucose infusion continues. Throughout the tracer study, blood will be taken from the second cannula at multiple time-points, to allow for measurement of glucose (including the tracers), insulin, C-peptide, glucagon, glucagon-like peptide 1 (GLP-1) and nonesterified fatty acids (NEFAs). A total of 150ml of blood will be taken during the tracer study. Urine is collected in two phases (before and after the meal) during the tracer study, for the measurement of glucose excretion. Indirect calorimetry will be used for twenty minute episodes at several time-points to measure substrate utilisation during the study. This involves the participant wearing a "hood" which is lightweight, and has a see-through visor. All of these measurements will enable us to model glucose fluxes in the participant and calculate indices of insulin sensitivity. Repetition of the tracer studies on two anti-hyperglycaemic agents will provide comparison of these indices on and off treatment.