I didn't think this was true, but apparently it is:
"This study of isolated gastric bypass with a 5.5-year follow-up rate of 88.6% revealed a success rate of 93% in obese or morbidly obese patients and 57% in super-obese patients. " (note that this is a specific type of gastric bypass) http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1421028/
"This study of isolated gastric bypass with a 5.5-year follow-up rate of 88.6% revealed a success rate of 93% in obese or morbidly obese patients and 57% in super-obese patients. " (note that this is a specific type of gastric bypass) http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1421028/