Duration: Individual subject participation will be approximately 15 months. Data will be collected at a baseline less than three months prior to surgery or before starting a Very Low Calorie Diet (VLCD), then at 6 and 12 months post surgery. The total duration, including enrollment, of the observational period for the cohort is expected to be 21 months. Subjects have the option to consent for future contact by investigators for a period of 10 years following their surgery.