Severe obesity (body mass index ≥40) has been linked to shorter survival, poorer mental and physical health, and substantial healthcare costs. Bariatric procedures, such as gastric bypass and gastric banding, dramatically reduce weight through gastric restriction, malabsorption, changes in neuroendocrine signalling, or a combination of these mechanisms.

One criticism of bariatric surgery has been the paucity of studies comparing its outcomes against non-surgical treatment. However, two recent controlled non-randomised studies found that bariatric surgery improved long term survival.1 2 The first was a prospective study that matched 2010 patients who had undergone bariatric surgery with 2037 non-surgical controls.1 After a mean of 10.9 years (with 99.9% follow-up), 6.3% of controls had died compared with 5.0% of surgical patients (hazard ratio 0.76, 95% confidence interval 0.59 to 0.99, number needed to treat 77). The second was a retrospective study of 9949 patients who had gastric bypass surgery and 9628 matched non-surgical controls.2 After a mean follow-up of 7.1 years, 4.1% of the control group had died compared with 2.7% in the surgery …