Are you referring to gastric bypass surgery, or bariatric surgery to remove portions of the colon for a patient's unresponsive crohn's disease?

Crohn's disease and bariatric surgery contain some similarities and are grouped within the same branch of medicine that deals with the intestines, stomach, and colon. Although the surgeries involved do not cure Crohn's disease or obesity, they aim to ease the pain and stress associated with these conditions, as well as correct the complications connected to chronic symptoms. Crohn's disease and bariatric surgery are for people who have not responded well to previous attempts to gain relief.

With Crohn's disease, a patient may face one of the two main types of surgery. The first deals with the drainage of abscesses that have accumulated on the bowel. Sometimes a part of the bowel is removed, which eliminates a blockage that was once present. Some individuals will undergo an ostomy, which deals with the removal of a section of their intestines. A new opening is then created for the body to release their bowel movements. Depending on the type of surgery selected, varying amounts and parts of the intestines are removed. For instance, in an ileostomy, the colon and rectum are removed, while the bottom section of the small intestine is attached to another created opening in the body.

I do not believe that having gastric bypass surgery causes Crohn's disease to develop, and I do not believe that this type of surgery is reccommended for individuals who have had Crohn's disease. That said, there are times when having a stressful incident in one's life, such as surgery, childbirth, or extreme stress can bring on the inflammatory reaction found in crohn's disease.

If I have not sufficiently answered your question, please feel free to expand on your original topic and I will fill in any gaps.