Department of Surgery and Cancer, Imperial College London, London, UK aruchuna@doctors.org.uk. Department of Public Health, Imperial College Healthcare NHS Trust, London, London, UK. Division of Surgery, Southampton Biomedical Research Centre, University Hospital Southampton, Southampton, UK. PsychoNeuroEndocrinology Research Group, Neuropsychopharmacology Unit, Centre for Psychiatry and Computational, Cognitive and Clinical Neuroimaging Laboratory, Division of Brain Sciences, Imperial College London, London, UK. Dietician, Imperial College London, London, UK. Division of Diabetes, Endocrinology and Metabolic Medicine, Imperial College Healthcare NHS Trust, London, UK. Imperial Clinical Trials Unit, Imperial College London, London, UK. Department of Diabetes and Endocrinology, University Hospital Southampton, Southampton, UK. Primary Care Medical Group, University of Southampton Medical School, Southampton, UK. Department of Surgery and Cancer, Imperial College London, London, UK. Division of Surgery, University Hospital Southampton NHS Foundation Trust, University Hospital Southampton, Southampton, UK.