It may seem as if everyone you know is avoiding gluten, but a new study from Rutgers New Jersey Medical School found that the incidence of celiac disease, the only medical condition proved to make the substance dangerous, is not changing.  However, the number of people who are eating gluten-free without a celiac diagnosis is rising.

Gluten consists of proteins in wheat and related grains that hold dough together. People with celiac disease have an immune reaction to the substance that damages the small intestine. Symptoms include diarrhea, weight loss, abdominal pain, and cramps, said Nikolaos Pyrsopaulos, chief of the gastroenterology division at the medical school and one of the study authors.

The study was published Tuesday in JAMA Internal Medicine. The  Rutgers team analyzed data from more than 22,000 people in the National Health and Nutrition Examination Surveys from 2009 to 2014.  They found that the percentage of people who tested positive for celiac through a blood test remained fairly steady at under 1 percent during all of the study years.  The percentage eating a gluten-free diet without a diagnosis  increased from 0.52 percent in 2009-10 to 1.69 percent in 2013-14.

The authors estimated that 1.76 million Americans have celiac disease while 2.7 million are on a gluten-free diet without a celiac diagnosis.

More people may be avoiding gluten, the researchers said, because gluten-free diets are perceived to be healthier, prepared gluten-free foods are easier to find, and more people have "self-diagnosed gluten sensitivity."  Hyun-seok Kim, an internal medicine resident at Rutgers who led the study, said the biggest increase in gluten-free diet followers was in young white women.

He said the question of whether some people who test negative for celiac disease can still be sensitive to the substance and benefit from a gluten-free diet is "highly debatable."  He sees no harm in people trying the diet to see if symptoms abate, but said that long-term, there could be nutritional deficiencies.

Pyrsopaulos sees little point in the diet without a diagnosis.  "It's not that it is bad," he said.  "If you don't need it, why?"

A related commentary by Daphne Miller of the department of family and community medicine at the University of California, San Francisco, said recent surveys have found that as many as a fifth of people in the United States have reduced or eliminated gluten in their diets.  While many people say they feel better on such diets, Miller said that a recent Italian study found that only 7.5 percent of participants experienced symptom relief on a gluten-free diet.

She raised the question of whether some other substance in grains is causing abdominal discomfort. Patients may also feel better on a restricted diet because their remaining choices may include healthier, less-processed foods.

"It is important that this choice not be dismissed as an unfounded trend except for those with celiac disease and wheat allergy," Miller wrote.  "Instead, researchers and clinicians can use this as an opportunity to understand how factors associated with this diet affect a variety of symptoms, including gastrointestinal function, cognition, and overall well-being."