Diabetes is common, affecting the health of nearly 1 in 10 UK adults. Complete remission is possible following bariatric surgery but is not universal. Previous literature has shown several parameters can predict remission. However, these predictors have, in most cases, not been translated into national guidelines and the accuracy of predictive scores incorporating them is limited in clinical practice. Additionally, the mechanism of remission is still not understood. The differing outcomes following bariatric surgery for people living with type 2 diabetes - remission or non-remission, provide a paradigm for exploring the mechanism of remission. In this thesis, a prospective observational cohort study was undertaken in those living with type 2 diabetes prior to and after weight-loss surgery to investigate predictors known to be involved in the aetiopathogenesis of type 2 diabetes. Participants had metabolic and gut hormone profiling to a
meal stimulus, body composition assessment and tissue sampling. In addition to validating predictors found in other cohorts, this thesis found novel predictors for remission including presence of microvascular complications, liver fat percentage and female lean mass/height2. Also, participants with worse baseline β cell function had a lower likelihood of remission. These predictors, if validated in a larger population, could be translated into an accurate and personalised predictive scoring tool to shape patient and clinician decision-making about bariatric surgery treatment. Mechanistically, this thesis also showed that metabolic improvement post-surgery was greater in remitters compared to non-remitters with differences in glucose, insulin, C-peptide and glucagon responses to a meal. The incretin gut hormone, GLP-1, changed significantly post-surgery but there was no evidence of a difference between remitters and non-remitters. This finding, in combination with evidence from this thesis showing worse β-cell function in non-remitters, suggests that β cell response to GLP-1 may be impaired in those who did not remit.