Incidence of type 2 diabetes after gastric by-pass surgery in a Swedish controlled cohort study

To assess the long-term risk of developing type 2 diabetes in patients with obesity who have undergone gastric bypass surgery compared to non-operated patients with obesity and the general population.

This study included 71,495 patients aged 20-65 years with a principal diagnosis of obesity in the Swedish Patient Register in 2001-2013. Of these, 23,099 had undergone gastric bypass and 32,435 had not. Each patient was matched by age, sex and geographic region with two controls from the general population without obesity diagnosis, i.e., 44,735 controls for the gastric bypass cohort and 62,522 controls for the non-operated cohort with obesity. Operated and non-operated patients with obesity were also directly compared using Cox regression analysis, providing hazard ratios (HR) with 95% confidence intervals (CI) adjusted for age, education, and sex.

During a median follow-up of 4.3 years (interquartile range [IQR] 2.4, 7.0 years), 3792 (11.7%) non-operated patients with obesity developed type 2 diabetes (incidence rate 22.8/1000 person-years, 95% CI 22.1-23.6) compared to 394 (1.7%) among gastric bypass patients (incidence rate 4.0/1000 person-years, 95% CI 3.6-4.5). The latter incidence was comparable to population controls (3.5/1000 person-years, 95% CI 3.2-3.8). Gastric bypass patients had 85% lower risk of diabetes compared to non-operated patients with obesity during the first six years of follow-up (HR 0.15; 95% CI 0.13-0.17).

Gastric bypass surgery for obesity seems to reduce the risk of developing type 2 diabetes to levels similar to that of the general population during the first six years of follow-up but not thereafter.