Gluten Does Not Cause GI Symptoms in Healthy People, Study Shows

Nicola M. Parry, DVM

September 11, 2019

Eating gluten-containing foods does not cause gastrointestinal symptoms in people without a gluten-related disorder, a double-blind, randomized, controlled trial (DRCT) published in the September issue of Gastroenterology shows.

"This is the first DRCT to demonstrate that consumption of gluten-containing flour does not generate symptoms in healthy volunteers," write Iain David Croall, PhD, from the Academic Unit of Radiology, University of Sheffield, United Kingdom, and colleagues.

"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)," they write.

Benjamin Lebwohl, MD, MS, director of clinical research, Celiac Disease Center at Columbia University, New York City, New York, emphasized to Medscape Medical News that "this well-done study addresses the widespread view in the public that gluten is unhealthy in the general population, even among those without known celiac disease or non-celiac gluten sensitivity."

Although gluten is safe to eat for people without a gluten sensitivity, endorsements from some celebrities and athletes have "cultivated" the perception that a gluten-free diet (GFD) is healthier, the authors suggest.

Indeed, market research has shown that 44% of Americans buy gluten-free food for reasons other than gluten sensitivity, and 65% believe that a GFD is healthier, according to the researchers.

Because of the need to differentiate people who benefit from a GFD from those who do not, Croall and colleagues conducted their study to determine how gluten affects healthy volunteers.

The Research

The study included 28 participants (female, N = 21; 75%) with a mean age of 38 years, all of whom underwent serological testing to detect celiac disease.

Each group attended two study sessions at a community venue and both groups were educated by a dietitian about a gluten-free diet.

They were then asked to undergo a gluten-free diet for 2 weeks and complete a Gastrointestinal Symptom Rating Scale (GSRS) to measure baseline abdominal pain, reflux, indigestion, diarrhea, and constipation. A visual analogue scale was also used to measure "global fatigue."

Next, the researchers randomly assigned participants to add sachets of gluten-containing or gluten-free flour to their food twice daily for 2 weeks. Those in the gluten group received 14 g of gluten protein daily. Participants in both groups continued their GFD during this time.

Participants completed the GSRS again at the end of the trial.

According to the authors, mean symptom scores decreased in the gluten group (suggesting symptomatic improvement) at the end of the trial, with only one participant in the gluten group reporting a worsening of some symptoms without improvement in others.

There was no significant difference between the groups with respect to changes in any of the symptoms (abdominal pain: treatment/control mean standard deviation [SD], −0.36 [1.95]/−0.29 [1.49]; P = .914; partial ETA2,  0.000; 95% confidence interval, −1.42 to 1.28).

However, the GSRS diarrhea score significantly decreased in participants in the gluten group (baseline/follow-up mean SD, 2.71 [1.94]/1.64 [0.92]; P = .033). This was probably an anomalous result, the authors note.

No other within-group analyses were significant.

The authors acknowledge some of the limitations of their study, including its short duration and the possibility that the trial may have unintentionally attracted participants with nonceliac gluten sensitivity or irritable bowel syndrome.

"As the GFD is not only thought to be no healthier than a "normal" diet, but has been suggested as overall suboptimal, there is possibly clinical justification in actively discouraging people from starting it if they have no diagnosable sensitivity," Croall and colleagues conclude.

One Caveat

The noneffect of gluten on these participants suggests that gluten does not cause gastrointestinal symptoms in most people, Lebwohl said. "One important caveat is that, during recruitment, these scientists identified (and excluded) two people who were found to have possible celiac disease on initial testing."

Thus, despite increased awareness of celiac disease and gluten, "there are still people with undiagnosed celiac disease out there, and gluten likely causes harm in that group," he added.

"So, if there is a concern, people should get tested for celiac disease before starting a gluten-free diet," Lebwohl said.

Among people who do not have celiac disease and yet report symptoms after eating gluten, he offered some potential explanations.

"Some have non-celiac gluten sensitivity," he explained, "some have an irritable bowel syndrome that responds to gluten restriction and, in some, it's a chance relationship that is not durable in the long-term."

This study was supported by the personal research funds of David S. Sanders. The authors have reported no relevant financial relationships. Lebwohl has reported serving as a consultant for Takeda and Innovate Pharmaceuticals.

Gastroenterology. 2019;157:881-883. Full text

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