I got a friend who had that done.
He had this rare bowel problem which I can't tell you the exact name, however the way it worked was that food pretty much went down a slipper slide once it when past his mouth.
This guy was as skinny as a twig because he couldn't absorb enough nutrients and calories without consuming HUGE amounts of foods and even then struggled, had to take massive doses of supplements for his nutrients and minerals.
Last year they did this operation (The donor was the doctor himself of all people) and 3 weeks later his body was a ton better, he was no longer a slipper slide, started putting on weight, he started looking better, feeling better and had energy, was happy...
Yeah the operation is kinda gross, BUT, it freakin worked and this guy a year later looks amazing! Although he's now fat, but at 42 and never having been able to put on weight at all (and no skinny guys with humming bird metabolisms have no idea what it's like) he's LOVING it hahaha.