Gluten-free diets continue to be popular with millions of Americans, despite the fact that there’s no evidence that such a diet is any healthier for most people than one that contains gluten.

The exceptions are people who have inherited the autoimmune disease known as celiac disease. For those individuals, eating gluten — a protein found in wheat and related grains, such as rye, barley and spelt — can damage the small intestine and lead to serious health complications.

People with celiac disease must follow a gluten-free diet. But they are a relatively small group — about 1 percent of the population.

Some other people have “gluten intolerance” or “gluten sensitivity,” which is sometimes referred to in the medical literature as nonceliac gluten sensitivity, or NCGS. Although the symptoms can mimic those of celiac disease — diarrhea, bloating and gas, abdominal pain, constipation, nausea and fatigue — NCGS does not cause damage to the tissue of the small intestines.

Most people who believe they are sensitive to gluten are not. A 2015 study found, for example, that more than 80 percent of people who reported gluten-related symptoms did not have celiac disease, NCGS or a wheat allergy.

Yet the fact that so many people falsely claim that they are gluten-intolerant has very real consequences for individuals with celiac disease or NCGS. It has meant that they face strong skepticism by family, friends and restaurants when they make dietary requests that are necessary for them to stay healthy.

A ‘gold standard’ study

It was for that reason that a group of British researchers decided to conduct what they say is the first double-blinded randomized controlled trial (considered the gold standard of medical research) on the effects of gluten on healthy people.

They recruited 28 healthy men and women, aged 19 to 63. The participants underwent a blood test to determine if they had celiac disease (none did) and filled out questionnaires to measure various symptoms associated with gluten intolerance, such as abdominal pain, indigestion, diarrhea, constipation and fatigue.

They were then put on a strict gluten-free diet for two weeks. At the end of that period, they were told to continue with the diet for another two weeks, but to also mix into their food each day a packet containing 14 grams of flour. Half of the participants were randomly assigned to receive gluten-containing flour, while the other half received gluten-free flour. Neither the participants nor the researchers knew which participants received which flour.

At the end of the two weeks, the participants filled out another detailed questionnaire. The study, which was published in the journal Gastroenterology, found that the people in the gluten-flour group were not more likely to report gastrointestinal symptoms or fatigue at the end of the study than those in the “placebo-flour” group.

“Our results support the view that gluten does not appear to cause symptoms in individuals who do not have a physiological susceptibility to it (ie, most of the population),” the study’s authors write.

Limitations and implications

This was a small study, and lasted for a relatively short time, although as its authors point out, other randomized controlled trials involving people with diagnosed NCGS have shown that symptoms of glucose intolerance can begin after just one week of eating gluten.

Despite those limitations, the researchers believe their findings suggest that people should be actively discouraged from starting on a gluten-free diet if they have not been diagnosed with either celiac disease or NCGS.

Fad diets are difficult to counter with facts, however, as an editorial that accompanies the study points out.

“Scientifically valid findings have to date had little influence on beliefs about gluten,” write the editorial’s authors, Emma Halmos and Peter Gibson, who are gastroenterology researchers at Monash University in Melbourne, Australia. “The psychology around a contested health phenomenon such as gluten avoidance involves active disenchantment with science and conventional medicine.”

One of those facts is that gluten-free diets are not always benign. It’s true that adopting a gluten-free diet can be healthy — if it leads people to reduce their consumption of processed foods and eat more whole foods, especially fruits and vegetables. It’s also true, however, that many gluten-free packaged foods are far from nutritional, for they are often high in fat, sodium and sugar and low in fiber.

“The big question is whether these findings will dampen enthusiasm for the use of a [gluten-free diet] among the general community,” say Halmos and Gibson.

Right not, they don’t seem very optimistic about that happening. Although the new study “has filled a gap in the gluten story,” they write, “it may do little to sway opinion regarding the notion that a [gluten-free diet] is a diet good for health.”

FMI: You’ll find abstracts of the study and the editorial on Gastroenterology’s website.