A new study has found that only one-third of people diagnosed with gluten sensitivity actually experience adverse side effects from gluten intake, adding further weight to the growing suspicion among scientists that gluten intolerance isn't actually a thing. Or at the very least, isn't as prevalent as we've been led to believe.

Right now, 'gluten-free' means big, big business. The New York Times reports that in the US, 30 percent of people say they want to eat less gluten, and the portion of households that are purchasing gluten-free products hit 11 percent last year, up from 5 percent in 2010. But not only are these products no more healthy for you than their gluten-packed counterparts, there appears to be very little science backing up many people's claims to needing them. 

The study, led by a team of gastroenterologists from the University and Spedali Civili of Brescia in Italy, involved recruiting 35 volunteers who had been diagnosed with non-celiac gluten sensitivity (NCGS). This condition is based on a small 2011 study that found gluten-containing diets can cause gastrointestinal pain in people who don't have caeliac disease - an autoimmune disorder that flares up with gluten intake. 

These volunteers had been living off a strict gluten-free diet for at least six months before the study, and were then asked to complete a series of "challenges" involving gluten-containing and gluten-free flours. Completely blind to what they were actually eating, the volunteers were given sealed sachets simply labelled "A" and "B", each containing 10 grams of flour. 

For the first stage of the experiment, the volunteers were given one type of flour and were told to sprinkle it over pasta or soup once a day for 10 consecutive days. They were then given 14 days to go back to their normal diets, and then repeated the challenge for another 10 days using the other type of flour. 

During the process, they were asked to report any symptoms of pain, reflux, indigestion, diarrhoea, and constipation, using a rating scale of 1 (no adverse effects) to 7 (severe adverse affects). Once they were all done, the volunteers had to guess which of the sachets contained the gluten-containing and gluten-free flours. If they guessed correctly, because their side effects linked up with the reality of what they had been eating, they were classified as having NCGS, regardless of the prior diagnosis. 

The researchers report that just 12 of the 35 volunteers could be classified as having NCGS based on these criteria. "Of the remaining subjects, 17 identified the gluten-free flour as causing symptoms and six reported no adverse symptoms during the trial whatsoever," Ross Pomeroy reports for Real Clear Science. "Also of note, most subjects tended to experience very mild symptoms throughout the trial. On average, participants rated the majority of gastrointestinal symptoms at 3 or lower on the aforementioned scale."

So what does this mean? While we have to take the results with a grain of salt because the sample size is so small and the symptoms were self-reported, they do agree with another recent study conducted in Australia that also suggests that for many people, gluten intolerance is all in their head. 

Jennifer Walsh reported for Business Insider:

"The [37 self-identified gluten-sensitive patients] cycled through high-gluten, low-gluten, and no-gluten ( placebo) diets, without knowing which diet plan they were on at any given time. In the end, all of the treatment diets - even the placebo diet - caused pain, bloating, nausea, and gas to a similar degree. It didn't matter if the diet contained gluten.

'In contrast to our first study… we could find absolutely no specific response to gluten,' Gibson wrote in the paper. A third, larger study published this month has confirmed the findings."

Both teams put their results down to the 'nocebo effect' - the anxiety felt by someone who thinks they're at risk of getting sick can sometimes actually make them feel sick - or perhaps the presence of carbohydrates called FODMAPS that some people could find hard to digest. But as far as gluten is concerned, it doesn't appear to be the menace we've been making it out to be.

"Our study has shown that gluten challenge leads to a recurrence of symptoms in only a third of patients fulfilling the recognised diagnostic criteria for the clinical diagnosis of NCGS," the Italian team concludes in the journal Alimentary Pharmacology & Therapeutics. "Consequently, NCGS is likely to be the correct diagnosis in only a minority of those who do not have celiac disease, but whom themselves choose to follow a gluten-free diet."