The global incidence and prevalence of obesity continue to increase, with the fastest rate of increase in the developing world. Obesity is associated with many chronic diseases including type 2 diabetes, cardiovascular disease and some cancers. Weight loss can reduce the risk of developing these diseases and can be achieved by means of surgery, pharmacotherapy and lifestyle interventions. Lifestyle interventions for prevention and treatment of obesity include diet, exercise and psychological interventions. All lifestyle interventions have a modest but significant effect on weight loss, but there is little evidence to indicate that any one intervention is more effective. There is evidence of an additive effect for adjunct therapy, and the combination of diet, exercise and behavioural interventions appears to be most effective for both the prevention and treatment of obesity.