Many factors influence post-op weight loss. One major factor is the surgery itself. The surgeon may not have performed the surgery in a way that provides optimal weight loss. Here’s an example: some surgeons create larger stomach pouches for their gastric bypass patients, which allows their patients to eat more food, consume more calories, and regain more weight. Another major factor is post-operative care. If a patient is not given proper instructions on how to eat, exercise, and hydrate, they might not be able to sustain weight loss over the long term. Long-term behavioral changes are necessary for weight loss to persist, even with the aid of bariatric surgery.