The aim of this trial is to evaluate the effect of a post-surgery 12-month lifestyle intervention compared to usual care upon post-surgery weight loss and changes that occur in body composition (relative amounts of body fat, muscle and bone), physical fitness and activity levels, diseases linked to obesity (e.g. diabetes, high blood pressure, high cholesterol level, sleep apnoea) and health-related quality of life (HRQoL) over a 12-month period.