We’ve all had friends who say they can’t eat gluten but don’t have celiac disease. If you’ve been wondering whether non-celiac gluten sensitivity is real, you’re not alone. We asked the experts.

For most people, there’s absolutely no reason to avoid gluten, according to Dr. Joseph Murray, a prominent gastroenterologist, and author of the book “Mayo Clinic Going Gluten Free.”

But why has Murray written a book teaching people how to avoid gluten — a protein found in wheat, barley, and rye — if it’s safe and nutritious?

“A number of patients who go gluten-free even though they don’t have celiac disease do better,” Murray said, “and when they go back to eating wheat they feel worse again.”

About 1 percent of the U.S. population suffers from celiac disease. For these people, eating gluten triggers an autoimmune response that damages the intestines and keeps nutrients from being absorbed properly.

People with untreated celiac disease can suffer from dramatic weight loss, vitamin deficiencies, chronic pain, diarrhea, fatigue, and, if they’re women, repeated miscarriages.

While celiac affects just 1 in 133 Americans, more than 10 times as many people shun bread, baked goods, crackers, and soy sauce because of the gluten they contain. A quarter of all Americans said in a recent food industry survey that they believed gluten was not nutritious.

In a 2014 Consumer Reports survey, 63 percent of participants said they felt following a gluten-free diet would improve physical or mental health.

And in a 2015 Gallup Poll, 21 percent of Americans said they try to include gluten-free foods in their diet.

In the gap between people for whom gluten prompts the body to turn against itself, and those who mistakenly think the protein is bad for them, sits a third group of people — estimates range from 0.6 to 6 percent of Americans — who suffer from non-celiac gluten sensitivity (NCGS).

These people have digestive, mood, and energy complaints that they believe are eliminated with a gluten-free diet. Blood tests show they do not have celiac disease antibodies. Intestinal biopsies show none of the damage that people with celiac disease exhibit. These people also don’t have a conventional food allergy to wheat.

In fact, modern medicine can’t find anything wrong with them. Yet, in response to an online call for NCGS sufferers, Healthline received reports of symptoms that emphasized bloating, diarrhea, and fatigue, but also included nausea, migraines, brain fog, irritability, mood swings, depression, achiness, joint inflammation, enlarged red blood cells, vertigo, and acne.

A study released in June 2016 did conclude that perhaps there is a blood test that detected a genuine medical condition for people who complain of these symptoms.

But that study involved only 80 people total, so the question remains.

Is NCGS a real condition?

Learn More About Celiac Disease »

Doctors and researchers have been looking for answers to that question.

With no tests to identify NCGS, it hasn’t been easy. Experts point to two influential studies.

The first, published in February, started with 118 Italians who said they had NCGS. The researchers eliminated half the volunteers for not meeting the condition criteria. They then tracked 59 participants through a placebo phase, when each received a small amount of rice protein every day, and a study phase, when each received gluten. Three participants exhibited more symptoms during the gluten phase.

Some hailed the study as proving that gluten sensitivity is real. But Dr. Stefano Guandalini, the founder and medical director at the University of Chicago Celiac Disease Center, who was not involved in the research, offered a different interpretation of the findings.

“There is a small, tiny, tiny, tiny number of patients who may be sensitive to gluten without having celiac disease,” he said.

Most celiac specialists take a similar view. They don’t dismiss gluten sensitivity outright — perhaps in part because dermatitis herpetiformis was initially not thought to be gluten related, but is now recognized as a manifestation of celiac disease.

Like Guandalini, most are skeptical that NCGS is anywhere near as widespread as people believe it is.

“I think [these patients] exist. They’re probably not that common, but they exist,” Murray said about people with NCGS, or what he calls “celiac-light.”

But if only a tiny number of people who report NCGS have a gluten-related condition, what’s going on with everybody else who complains of digestive woes?

They probably fall into several groups. Some may be in the early stages of celiac disease and the disease hasn’t yet produced any of its telltale signs, Guandalini said. Others are likely allergic to wheat.

Many may be sensitive to fermentable oligo-, di-, and monosaccharides and polyols (FODMAPs), which are certain types of carbohydrates including wheat, lentils, and mushrooms that can draw water into the intestine and potentially ferment, causing digestive problems for some people.

This is what the second influential study on gluten sensitivity found. The 2013 study suggested that intolerance to the carbohydrates in wheat might account for what many believe is a bad reaction to gluten.

The Australian research team behind the study had previously shown that people who self-identified as having NCGS did better on a gluten-free diet even when they didn’t know if they were eating gluten or not. When they launched a second study, they expected to confirm these results.

But they didn’t. This time around, the researchers first reduced FODMAPs in the participants’ diets. Then they reintroduced gluten or a placebo. There was absolutely no difference in participants’ reactions.

The Australian team concluded that most people who thought they couldn’t tolerate gluten were in reality sensitive to FODMAPs. Once they had cut consumption of these carbohydrates below a certain threshold, gluten posed no problem for them.

Food also has a strong placebo effect. Some people may feel better on a gluten-free diet simply because they expect to. There’s a corresponding “nocebo” effect that leads people to feel worse again when they are exposed to the thing they believe is bad for them.

Many people who give up gluten wind up eating less initially, Murray said. And for people with digestive problems, eating less can make them feel better.

“It’s just not a very sustainable solution,” he added.

Eliminating all of these alternate explanations, only a tiny number of people remain whose gastrointestinal problems are unexplained.

Learn More About Dermatitis Herpetiformis »

For such a small group, an awful lot of ink has been spilled over those with NCGS.

The criteria for NCGS that doctors have developed disguise the fact in an elaborate flowchart, but “currently it’s a patient diagnosis,” said Dr. Peter Green, director of the Celiac Disease Center at Columbia University.

Celiac support groups seem to share the view of gluten sensitivity as a real but inflated diagnosis.

“There were always people who just did better removing gluten from their diet, but we didn’t know why,” said Mary Schluckebier, Executive Director of the Celiac Support Association, a national group based in Nebraska. “It’s probably a family of diseases, and we don’t have good names for any of it yet.”

But Schluckebier also described something else that may be driving the rise of NCGS.

“A patient goes to the doctor, and they want a diagnosis. ‘Don’t tell me I don’t have this — give me a name for it,’” she said. “So doctors came up for a name for it. I think it was a way to appease impatient patients. I don’t know how to say that nicely.”

Alice Bast, the president and chief executive officer of Beyond Celiac, formerly the National Foundation for Celiac Awareness, based in Ambler, Pennsylvania, found emotions are a common cause with people who have NCGS.

“They want research, they want to know what’s happening to their bodies. You want to feel better. You want to live life to the fullest. You don’t want to live life in fear of food,” Bast said.

People with celiac disease see advantages in the growing interest in gluten-related problems, so they’re reluctant to disregard them. Schluckebier described watching the number of studies on celiac and related conditions explode on the PubMed database.

The “impatient patients” who believe they have an unrecognized condition “may be helping drive some of the researchers who were never interested in this before,” Schluckebier said.

People with celiac disease have seen more immediate benefits, too. Bast described ordering food from an obscure Canadian company when she was first diagnosed with celiac disease more than 20 years ago. Now she can buy gluten-free food in Walmart and Whole Foods Market.

A study published last summer actually concluded a gluten-free diet doesn’t do much for people who don’t have celiac disease.

Nonetheless, gluten-free foods are expected to be a $6.6 billion market by 2017, according to the market research firm Packaged Facts. Food companies have pushed gluten-free foods through marketing efforts because the foods cost more. They’ve also sponsored some celiac awareness groups. The Celiac Disease Foundation gets most of its money from corporations, including General Mills and Frito-Lay.

For those with celiac disease, the increased availability of specialty products is a boon.

“We love people buying gluten-free food,” Bast said. “It increases availability and affordability. It gives us access to food.”

Doctors and people with celiac disease all agreed, however, that most packaged gluten-free foods are not healthy.

“Gluten-free junk food is still junk food,” Bast said.

Increased awareness of NCGS hasn’t been all good news for people with celiac disease. It’s gotten easier to buy gluten-free pastas and baked goods, but it’s become paradoxically more dangerous for to eat out at restaurants.

“Celiac disease is a real disease with real consequences. But the treatment for their disease has been trivialized, especially by restaurants,” Murray said.

Restaurants offer lots of gluten-free foods, and the vast majority of people who avoid gluten will do fine with a Caesar salad served with croutons that can be picked off. However, most people with celiac disease cannot tolerate lettuce that has been contaminated with gluten.

“We talk to people who have a medical necessity for gluten-free food,” Bast agreed. “The overuse of the term gluten-free undermines the disease concept.”

With all the buzz about gluten sensitivity, many have come to see gluten as something best avoided, just in case.

It’s not.

“People need to know that gluten is not inherently bad. There’s nothing about it that results in poor health or disease. It’s something that our bodies can metabolize without any problems for the most part,” said Lisa Cimperman, M.S., R.D., L.D., and a spokesperson for the Academy of Nutrition and Dietetics.

We asked Murray, who wrote the book on going gluten-free, if he eats wheat.

“Do I eat wheat? I’m eating wheat right now,” he said. “Wheat is the basis of western civilization. Without wheat there wouldn’t be a civilization.”

There should be no guilt about eating gluten as part of a healthy diet. But what should you do if you have genuine stomach troubles that you believe are linked to gluten?

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It can be hard for people who believe gluten triggers their digestive woes to get a diagnosis.

“Let’s say someone is having issues with abdominal pain, bloating, diarrhea, constipation — you know, general GI symptoms,” said Cimperman. “Their first step should be to talk to physicians because the doctor needs to rule out any medical conditions that can be treated, say something like irritable bowel syndrome or actual celiac disease.”

Instead many people who have GI symptoms hear that gluten is a potential irritant and try going gluten-free on their own. But testing for celiac disease and wheat allergies relies on continued exposure to the suspected foods.

Doctors say it can be hard to persuade people who have already stopped eating gluten to go back to eating it for a few weeks as a trial.

“The fact that it’s a self-diagnosis really deprives people of getting the correct diagnosis, which might be celiac disease,” Green said.

People who have celiac disease need to know. Because the intestine suffers damage every time gluten is introduced, these people should never eat gluten or even share pots and pans with family members who do eat gluten. That kind of discipline can be hard without a concrete diagnosis.

Those who believe they have NCGS might actually have a wheat allergy, which would mean they could eat rye and barley but could not drink wheatgrass juice, as people with celiac can.

A gluten challenge doesn’t have to be as grueling as people think, Guandalini said. First, all people with celiac disease share a particular genetic pattern. It’s the marker of their risk. So a genetic screening can help determine whether someone needs to undergo a gluten challenge at all.

For those who need to do a gluten challenge to rule out celiac disease, the process may be shorter and less painful than they expect. Doctors used to say it took four weeks to elicit and identify signs of celiac disease, but newer research suggests two weeks is enough. And a gluten challenge involves such a small amount of the protein that only those with relatively severe celiac disease would feel sick from it.

For people whose genetic screening rules out celiac disease, the lack of a diagnosis can be frustrating, for sure. But there’s an upside, too.

“You can tell them, look, there is no test [for NCGS], but you certainly don’t have celiac disease, so go ahead with a gluten-free diet or abandon it. Enjoy your life, do what you want,” Guandalini said.

Cimperman takes a similar approach. If people continue to feel better on a gluten-free diet, she tells them to make sure they get enough fiber and vitamins B and D, and sends them on their way.

“If their symptoms are better on a gluten-free diet, I’m not going to change it. If it’s not broke, don’t fix it,” she said.

But in the majority of cases when gluten isn’t really the problem, symptoms return after a few weeks. Murray said these people then begin chasing the brief improvement they had — probably from giving the gut a rest by eating a little less — or by eliminating more and more foods.

Instead, the science shows, these people should try a low-FODMAP diet.

Though the FODMAP elimination diet is “pretty intense,” as Cimperman put it, people who cut out the foods that are at the root of their troubles will get long-term results. Eventually, they will likely be able to reintroduce higher FODMAP foods.

Editor’s Note: This story was originally published on April 16, 2015 and was updated by David Mills on August 12, 2016.