Gluten-free diets may actually be low-gluten diets, study suggests

January 29, 2020

Gluten found in food, urine and stool samples from celiac disease patients

By Amy Ratner, Medical and Science News Analyst

Two thirds of patients who were strictly following a gluten-free diet still showed signs of having consumed gluten in the most recent DOGGIE Bag study analysis.

The DOGGIE Bag study is an innovative approach to determining how much gluten celiac disease patients who don’t knowingly eat gluten actually consume and how much they excrete through urine and stool samples. Researchers also looked at results of blood tests for antibodies to gluten and the amount of intestinal damage shown through biopsies of the small intestine.

“Our novel findings support the general concern that a gluten-free diet may be more aspirational than achievable, even by highly committed and knowledgeable individuals,” wrote study author Jocelyn Silvester, MD, director of research of the Celiac Disease Program at Boston Children’s Hospital, and colleagues. “This issue likely underlies persisting symptoms and incomplete mucosal recovery.”

Gluten test results

Eighteen adults with celiac disease who are part of a Manitoba Celiac Disease study cohort participated in the 10-day study. Study participants sent in a quarter portion of the foods they ate for seven days to give researchers a way to measure the amount of gluten consumed. Researchers tested the food and the urine and stool samples for gluten immunogenic proteins (GIP).

Study participants were told to follow their usual diet, including eating at restaurants and in other’s homes. They filled out questionnaires detailing their symptoms and how they followed the gluten-free diet.

Related: Learn more about the DOGGIE bag study

Twenty five of 313 food samples collected from 9 participants had some amount of gluten, the study analysis published recently in the journal Gastroenterology found. Of those, 40 percent had more than 20 ppm. Twenty percent had more than 200 ppm, which is more than 10 times the allowed amount.

Additionally, 6 percent of 519 urine samples from 8 participants contained detectable amounts of gluten and 11 percent of 75 stool samples from five participants were positive for gluten.

Blood tests and biopsies

However, the study found that blood tests that measure antibodies to gluten did not correlate closely with gluten exposure. In fact, 64 percent of those whose TTG levels were normal were exposed to gluten by one measure or another.

Researchers reported some lack of agreement between gluten detection and damage to the intestine, called villous atrophy. Although everyone in the study showed improvement over time, nearly 60 percent had persistent intestinal damage.

Two thirds of study participants who had a positive sample for gluten had persistent intestinal damage, and two thirds of those who had no positive sample for gluten had normal intestines. However, two thirds of patients with no intestinal damage had at least one positive sample.

“Our results suggest that most celiac disease patients in actuality follow a low-gluten diet, and complete elimination of dietary gluten may not be possible to maintain.”

One possible explanation could be that some of the extremely low levels of gluten detected where not sufficient to cause damage to the villi, according to the study. “Perhaps both the amount and the duration of gluten exposure are important determinants of [damage shown through a biopsy], the researchers wrote.

“Our results suggest that most celiac disease patients in actuality follow a low-gluten diet, and complete elimination of dietary gluten may not be possible to maintain.” 

Another possibility is that in the relatively short study, participants might have “intensified” their diligence in following the gluten-free diet.

That kind of change in behavior as a result of being observed, called the Hawthorne effect, has occurred in other celiac disease studies, making it difficult to reliably determine what a real-world gluten-free diet is like.

“Even though typical ‘real world’ gluten exposures may have been underestimated, this study confirms that gluten ingestion occurs frequently despite efforts to follow a strictly gluten-free diet,” the authors wrote.  “Our results suggest that most celiac disease patients in actuality follow a low-gluten diet, and complete elimination of dietary gluten may not be possible to maintain.”

Preliminary results from the DOGGIE Bag study were initially shared at Digestive Disease Week in 2018. Additional details are expected to be included in future journal publications. In addition to Silvester, the study was done by researchers from the Harvard Medical School Celiac Research Program, Beth Israel Deaconess Medical Center, the University of Manitoba, the University of Seville and St. Boniface Hospital.

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