Gut Hormones and Roux en Y Gastric Bypass

Inclusion criteria * Aged 18 - 70 years. * Male or female. * Eligible for bariatric surgery under the NHS. * Diagnosed with impaired glucose regulation or type 2 diabetes, according to WHO 2011 criteria. * Those with diabetes should be stable and well controlled with either diet or one oral hypoglycaemic agent. * HbA1c ≤9.0% or 74.9 mmol/mol. Exclusion criteria * History of any medical, psychological or other condition, or use of any medications, including over-the-counter products, which, in the opinion of the investigators, would either interfere with the study or potentially cause harm to the volunteer. * Without access at home to a telephone or other factor likely to interfere with ability to participate reliably in the study. * Pregnancy or breastfeeding. * Smokers. * Unable to maintain adequate contraception for the duration of the study and for one month afterwards. * History of hypersensitivity to any of the components of the subcutaneous infusions. * Donated blood during the preceding 3 months or intention to do so before the end of the study. * Insulin treatment. * Uncontrolled hypertension. * Any other co-morbidity that would compromise the validity of the study or the safety of the participant such as heart failure, clinically apparent cardiovascular disease. * Volunteers on anti-coagulants such as warfarin and factor Xa inhibitors will not undergo adipose tissue biopsy. * Unable to give informed consent. * Previous bariatric surgery. * Unable to undergo fMRI due to: * Claustrophobia. * Pacemaker, metal implant, clips, implanted device, shrapnel or bullet, metal in eyes that precludes magnetic resonance imaging. * Significant structural abnormality on magnetic resonance brain scan