A meta-analysis by Simoneau M et al. on hormone changes before and after RYGB in patients with obesity showed that, at 26 and 52 weeks postoperatively, four studies reported fasting total PYY levels of 116 pg/ml (95% CI: 107–125) and 123 pg/ml (95% CI: 104–142), respectively. This evidence concerns the gene PYY and Obesity.