The production of controlled intestinal malabsorption by surgically short-circuiting the small intestine. This procedure is used to treat massive obesity. It is done by anastomosing the proximal jejunum to the distal ileum by bypassing the small intestine between the anastomotic sites. The lengths of jejunum and ileum involved vary by surgeon. Because of longterm metabolic complications (including hepatic injury), this procedure has largely been abandoned in favor of gastric bypass procedures.