Within the UK Biobank, severe obesity was defined as BMI ≥ 40 kg/m2 (NHLBI Expert Panel, 1998). Additional phenotypes with respect to disease status and bariatric surgery were ascertained via linkage to data based on self-report in an interview with a trained nurse, and diagnosis and procedure codes within the electronic health record. Bariatric surgery status was ascertained based on having a OPCS-4 primary procedure code for Roux-en-Y gastric bypass, sleeve gastrectomy, or duodenal switch procedure (G28.1–5, G31.2, G 32.1, G33.1, G71.6).
