Yes, it is possible to gain weight back after gastric bypass surgery if a person fails to eat properly or do appropriate exercising. Some websites that have information on ways to avoid gaining weight back after gastric bypass surgery are as follows: forums.webmd.com/3/diet-exchange/forum/845, www.bariatric-surgery-source.com/weight-gain-after-gastric-bypass.html, and www.wral.com/lifestyles/healthteam/story/4330107.