"Thirty percent of Americans https say theyre trying to reduce or eliminate gluten in their diets. But only about  percent of the population has an autoimmune response to gluten. Somewhere in that gap a diet fad is thriving. There are two groups of people who should definitely avoid gluten those diagnosed with wheat allergies and those who have celiac disease. The latter is more common affecting about  percent of the population. The former affects perhaps . percent of people http and is more common in children who often grow out of it. What is less clear is whether there is another group of individuals whose digestive systems have some gluten sensitivity and who would therefore benefit from avoiding gluten. The people who think theyre sensitive to gluten are filling the gap between those who should avoid gluten and those who are doing it anyway. But how many people really are sensitivehttpsfivethirtyeight.comfeaturesitshardtoknowwhereglutensensitivitystopsandtheplaceboeffectbegins Gluten for those of you who have not kept up with dietary fads is a component of wheat. You eat it in bread pasta pizza and so on. Glutenavoiders are helped by an increasing array of glutenfree breads pastas and other products. Entire aisles of Whole Foods Market stores appear to be devoted to this trend. Despite the growing availability of alternative products avoiding gluten can be a challenge. The satisfying slightly chewy texture of bread requires gluten. For those of us who care about our health but lets face it like a nice baguette it seems worth asking Is there any actual health benefit to gluten avoidance The earliest report on whether gluten could muck with some digestive tracts comes from the late s http Two authors reported on a woman in her early s who was experiencing significant gastrointestinal distress bloating gas diarrhea constipation etc. and did not have celiac disease or a wheat allergy. After being put on a glutenfree diet she improved immediately. When gluten was reintroduced to her diet as a test the symptoms returned only to disappear when the gluten was again removed. The authors diagnosed the woman with what they termed nonceliac gluten sensitivity NCGS. Gluten sensitivity fell off the radar for many years but researchers have returned to it http and adopted the same term. In contrast to celiac disease or a wheat allergy NCGS is not diagnosed through direct testing. Rather it refers to a condition in which someone experiences some problematic gastrointestinal symptoms that resolve when gluten is avoided. Gastrointestinal symptoms are the hallmark of NCGS  although some people also complain of fatigue or a foggy head. Of course its difficult to distinguish between someone who is sensitive to gluten and someone who is sensitive to the placebo effect. Since there is no test for gluten sensitivity diagnoses are based on whether people say they feel better when they avoid gluten. But the mind is a powerful thing. If you think avoiding gluten will make you feel better there is a reasonable chance that it will  even if gluten is irrelevant. This effect makes it hard to test for gluten sensitivities even in a randomized controlled trial. If a researcher enrolls people in a standard randomized controlled trial and has some participants eat bread and some not those who avoid bread may feel better simply because they think they should. The placebo effect may lead a researcher to falsely conclude that avoiding bread is beneficial. But thats not enough. To really get a sense of whether gluten sensitivity is a thing researchers need to conduct a doubleblind randomized controlled trial in which one group eats gluten another does not and no one knows which group they are in. That means putting everyone on a glutenfree diet and then directly supplementing some people with gluten protein and others with something that seems similar but has no gluten. There have been two small studies like this. They were run by the same team. And unfortunately for our ability to draw conclusions they find different results. The first of these http published in  followed  people for up to six weeks. The study population was made up of people who complained of gastrointestinal symptoms consistent with NCGS. Everyone participating in the study was on a glutenfree diet. Half had their diet supplemented with a regular muffin and regular bread the other half received a glutenfree muffin and glutenfree bread. The authors found that  percent of patients on the entirely glutenfree diet reported a continuation of symptoms compared with  percent of those who had consumed gluten. The groups also differed on such measures as satisfaction with stool consistency a phrase that I honestly never thought I would write. The second study http published in  had a similar set up   people complaining of gastrointestinal problems randomized into highgluten lowgluten and nogluten groups. This time rather than using bread and muffins the authors used gluten and whey protein supplements. They found no difference in symptoms among the groups. Why the results of these studies differ is unclear. One possibility is that some participants in the first study guessed which group they were in based on the muffin and bread and therefore the placebo effect became pronounced. Another possibility is simply that given how small the studies were the differences occurred by chance. Regardless of the reason we are left with little convincing evidence that gluten avoidance matters. But lets say you take heart in the first of these studies and now believe that avoiding gluten will make some people feel better even though they dont have an allergy or celiac disease. How many people Estimates of prevalence of NCGS are based more or less on information on gluten avoidance http In the  National Health and Nutrition Examination Survey http about . percent of people without celiac disease or an allergy say their diet is glutenfree. And in a large Italian study http of people who complain of gastrointestinal problems the authors conclude that NCGS is slightly more common than celiac disease putting it at a prevalence of a bit above  percent of the population. For those of you keeping track at home that means that while  percent of Americans are trying to cut gluten from their diet probably at most only  percent of Americans may have NCGS. If you dont have celiac disease or a wheat allergy and are experiencing distressing gastrointestinal symptoms after eating gluten  lack of satisfaction with your stool consistency for example  there is something like a  in  chance that the gluten is potentially responsible. If you cut out gluten and it makes you feel better great. Although it may all be in your head. If you are cutting out gluten for any other reason all that will happen is youll feel the same but without the pleasure of bread that tastes like bread. CORRECTION Feb.   a.m. An earlier version of this article incorrectly state that it is hard to test for gluten allergies. Its hard to test for gluten sensitivities. The previous version also misstated the probability that gluten is responsible for gastrointestinal distress for those who experience gastrointestinal distress after consuming gluten and who dont have celiac disease or a wheat allergy. The probability is  in  not  in ."