In 2011, gastroenterologist Peter Gibson published the results of a study that provided some of the strongest evidence to date that gluten can cause stomach problems in people without celiac disease. But Gibson has since called the results of his first study into question, with a rigorous followup investigation.
Ross Pomeroy sets the scene over at Real Clear Science:
…like any meticulous scientist, Gibson wasn't satisfied with his first study. His research turned up no clues to what actually might be causing subjects' adverse reactions to gluten. Moreover, there were many more variables to control! What if some hidden confounder was mucking up the results? He resolved to repeat the trial with a level of rigor lacking in most nutritional research. Subjects would be provided with every single meal for the duration of the trial. Any and all potential dietary triggers for gastrointestinal symptoms would be removed, including lactose (from milk products), certain preservatives like benzoates, propionate, sulfites, and nitrites, and fermentable, poorly absorbed short-chain carbohydrates, also known as FODMAPs. And last, but not least, nine days worth of urine and fecal matter would be collected. With this new study, Gibson wasn't messing around.
The details of the investigation are recounted at RCS, but here's the upshot: Gibson's team found that test subjects who self-identified as suffering from non-celiac gluten sensitivity reported a worsening of gastrointestinal symptoms (pain, bloating, nausea, gas) whether their treatment diet included gluten or not. The results, Gibson's team says, are indicative of what's called a nocebo effect – "nocebo," here, referring to a harmless substance (gluten) which, when ingested, is experienced as harmful by the receiving test subject. Says Gibson: "In contrast to our first study… we could find absolutely no specific response to gluten."
In other words, it's possible that the stomach problems many people pin to gluten intolerance may actually be due to something else. One culprit could be the FODMAPS mentioned earlier. (There's a lot of overlap between dietary sources of FODMAPS and dietary sources of gluten, so abstaining from the latter would amount to, inadvertently, abstaining from the former.) On the other hand, the observation of a nocebo effect suggests gluten sensitivity in some people who self-identify as being non-celiac gluten sensitive could actually be psychological.
There is obviously more research to be done here, but Gibson's results should certainly give one pause. They are enough, at the very least, to make one wonder whether America's dramatic shift away from gluten products in recent years (by some surveys, 30% of Americans say they "would like to cut back on the amount of gluten [they're] eating") has been driven more by fear, fad-dieting, and the meteoric rise of what is today a multi-billion-dollar gluten-free industry than conclusive scientific evidence.