Meanwhile, a gluten-free diet may not always be needed for those who have IBS
By Amy Ratner, director of scientific research
In some cases, people with irritable bowel syndrome (IBS) may actually have celiac disease, while in others they may be unnecessarily following the gluten-free diet, according to two recent studies investigating IBS.
IBS should not be diagnosed without excluding celiac disease, concluded a study by researchers from the UK and Italy published in the American Journal of Gastroenterology. The study found that 6 percent of those with IBS had positive blood tests for celiac disease.
A second study by Canadian researchers from McMaster University and colleagues published in The Lancet Gastroenterology and Hepatology found that a number of people with IBS who think gluten or wheat are harmful are not actually sensitive to these ingredients. Participants who thought wheat or gluten was in cereal bars they ate as part of the study reported symptoms even when these ingredients were absent.
“These findings suggest that expectations played a major role in symptom generation,” the study concludes, noting that only some IBS patients benefit from a gluten- or wheat-free diet.
Taken together, the studies point out the complexity of the relationship between celiac disease, the gluten-free diet and IBS.
Worldwide it’s estimated that 5 to 10 percent of the population has IBS, compared to about 1 percent with celiac disease. In celiac disease, up to 50 percent of cases remain undiagnosed.
IBS and celiac disease
In the first study, 6 percent of about 7,000 IBS patients had a positive blood test for celiac disease, a review of nearly 30 studies done from 2006 to 2025 found. The review also included about 1,700 controls who did not have IBS. Those with IBS were diagnosed with measures established in 2006.
Patients with IBS had four times the odds of having positive celiac disease blood tests compared to controls, the review study found.
“Our results support the current recommendation that a positive diagnosis of IBS should not be made without excluding celiac disease,” the authors wrote.
Symptoms of IBS and celiac disease overlap, including recurrent abdominal pain, but only untreated celiac disease is associated with long term complications, such as nutritional deficiencies, osteoporosis, infertility and increased mortality, the authors wrote.
When celiac disease is misdiagnosed as IBS it “could lead to prolonged symptom burden, delayed treatment and increased risk of preventable complications,” the study says.
One of the limitations of the review is that it included no studies from the United States. The authors wrote that blood tests for celiac disease have been part of the routine work-up for suspected IBS in the United States and Europe for more than a decade. This limited the number of groups of patients who had not been tested for celiac disease from these regions, they said.
However, recent analysis of U.S. private health insurance data from 2007 to 2022 by Beyond Celiac presented at Digestive Disease Week found that although IBS is among conditions that should lead to celiac disease testing, there are often long delays before testing occurs.
Biopsy-proven celiac disease
In the 20 studies that reported on those who had gone on to have a biopsy for definitive diagnosis, about 2 percent of nearly 6,000 patients with IBS had celiac disease, researchers found.
The authors wrote that a significant portion, 15 percent, of those who with IBS who had positive celiac disease blood test results did not go on to get an endoscopy and biopsy. Patients often refused the to get the endoscopy and biopsy, with the study saying it was likely due to concerns about the invasive nature of the procedures. A no-biopsy approach to diagnosis when blood tests indicate it’s appropriate could help solve the problem, they suggest.
IBS and the gluten-free diet
In the second study, which investigated IBS and the gluten-free diet, about 30 study participants who believed they were sensitive to gluten and followed a gluten-free diet were evenly divided to get cereal bars that contained whole wheat, gluten or neither. They did not know which group they were in.
In all groups, including the ones with bars that did not contain gluten or wheat, 93 percent of participants reported having symptoms.
This kind of reaction is called the nocebo effect, where patients develop symptoms because they anticipate negative effects will be triggered. It’s the opposite of the placebo effect, where patients feel better because they think they will.
Still, some IBS patients legitimately benefit from diets that exclude gluten or wheat, the study says. These IBS patients should be identified, the authors wrote. In those who don’t benefit, wheat and gluten need to be destigmatized, they noted, and psychological counseling to reintroduce these ingredients in the diet may be helpful.
Reluctance to give up the gluten-free diet
“Most patients continued a gluten-free diet despite learning that neither gluten nor wheat was triggering their symptoms,” the study says, noting this suggests patients were entrenched in their belief systems. These beliefs about harm were strong and persistent for the long term. Following the gluten-free diet may be one of the few ways patients feel they can take control of their IBS, the study suggests.
Those who did abandon the gluten-free diet usually did so because of financial constraints or difficulty following the diet.
After being given the cereal bars, study participants reported symptoms as well as whether they had eaten the bars, which all had the same appearance, taste and smell. Though most claimed that they ate all the bars, little or no gluten found in stools tests even among those who received gluten-containing bars suggested that many had avoided consuming them.
Still, gluten getting into the gluten-free diet was an issue for most study participants. Despite expert dietitian advice on maintaining the diet at the start of the study, gluten was found in stool tests of nearly 70 percent of study participants before they ate the cereal bars containing gluten or after eating the bars that did not contain gluten. Study authors attributed this to the cross-contamination and the difficulty of maintaining a gluten-free diet.
The study is not a definitive trial for all IBS patients, the authors wrote, noting several limitations. They call for larger studies to confirm their results.
You can read more about the celiac disease study here and the gluten-free diet study here.