Obesity and type 2 diabetes are major causes of illness and premature death worldwide and their incidence is increasing rapidly. Bariatric surgery is considered as the gold-standard surgical treatment for both conditions. However, not all patients do equally well after surgery and indeed the weight loss experienced by patients undergoing bariatric surgery can vary. As such when patients are seen after bariatric surgery in clinic they fall in one of the following two categories: 1. Good responders: this is the majority of patients who lose the expected amount of weight based on the published studies. 2. Poor responders: this is a small group of patients who either lose less than the expected amount of weight after bariatric surgery or lose the expected amounts of weight early after surgery but then regain a substantial proportion of the weight they have lost. The so-called poor responders are exposed to all the risks of the operation and do not benefit from the weight loss as much as good responders. This study would therefore like to investigate the physiological factors that distinguish poor from good responders before, and after bariatric surgery. The study team hypothesizes that compared to good responders, poor responders exhibit: 1. a smaller degree of fullness sensation after a meal, 2. a lower energy expenditure after a meal, and 3. genetic changes (single nucleotide polymorphisms) that predispose the poor responder to development of obesity. In addition, the study team hypothesizes that poor responders exhibit: 1. lower gut hormone secretion after a meal and 2. are less sensitive to the physiological action of gut hormones compared to good responders and that this difference in gut hormone secretion and response to gut hormones prior to bariatric surgery can be helpful to predict response to bariatric surgery.