The prevalence of obesity is increasing dramatically all over the world, leading to suffering as well as high health care costs due to obesity-related co-morbidity. Long-term results from weight loss studies are hard to attain due to the difficulties in sustaining weight losses. Gastric surgery results in large and maintainable weight reductions. The Swedish obese subjects (SOS) study offers a unique possibility for investigating the effects of weight loss as compared with weight stability in obese subjects over a long period of time.