I know this post is older but, yes, they are starting to discover marginal ulcer rates as high as 25% (although the rates vary from study to study. You also have to understand that includes small ulcers that heal or show no symptoms, not the big, problem causing ones that are a cause for revision surgery). The reason is because of the surgery itself: they're connecting the jejunum up to your stomach. The jejunum usually connects to the bottom of the duodenum. The duodenum releases bicarbonate to reduce acid intensity and by the time the chyme (mushed up food content from your stomach) reaches the bottom of the duodenum, acidity is fairly low. That sort of acidity the jejunum can handle. Now that the jejunum is connected directly to the stomach, the acidity of the food that travels down it is much higher. The jejunum toughens up a bit over time and it has its own defences, but not to the level of the duodenum. So the chances of ulceration can be (not with everyone, but sometimes) much higher. This is why they won't do this operation for people who smoke or take NSAIDs. In an operation that increases ulcer risk, operating on people who are guaranteed to get an ulcer already is contraindicated. My advice would be to never smoke, take NSAIDs, and try and take something like zinc carnosine or l-glutamine to help support the tissue integrity of your jejunum to reduce the chances of ulcers forming.