The Poor Responders Study

Inclusion Criteria: * Aged 18 -70 years. * Male or female. * Previous bariatric surgery for obesity and/or diabetes (studies 1 and 2). * ≥1 year interval after bariatric surgery (studies 1 and 2). * Awaiting bariatric surgery at the Imperial Weight Centre (study 3) * Able to give informed consent. 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. * 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. * Any other co-morbidity that would compromise the validity of the study or the safety of the participant such as heart failure or clinically apparent cardiovascular disease. * Anatomical or endocrinological pathology causing poor weight loss or weight regain * Uncontrolled hypertension (systolic blood pressure of 160 mmHg or above and/or diastolic blood pressure of 100 mmHg or above) * Participation in a research study within the last two months. * Unable to speak English (this is relevant to answering the psychological questionnaires)