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Celiac disease researchers examine the content of patients' doggie bags

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Study seeks to measure how much gluten celiac disease patients consume even when they are on a gluten-free diet

By Amy Ratner, Medical and Science News Analyst

There are two ways you could interpret the name of the new Doggie Bag study, which investigates how much gluten people with celiac disease are getting in their diets. And each would be correct.

Participants in the study provided portions of all the food they ate over 10 days – what you could think of as the doggie bag you bring home from a restaurant. They also provided stool samples, which might bring to mind the bags dog owners use to clean up after their pets.

Either way, the name reflects the commitment made by 18 celiac disease patients on the gluten-free diet who took part in the 10-day review of all the gluten going in and coming out of their bodies. Urine samples were also collected.

Celiac disease researchers tested all the samples for the presence of gluten immunogenic peptides (GIP) and concluded that 66 percent of the patients trying to follow a strict gluten-free diet showed evidence, by one measure or another, of being exposed to gluten. The amount of gluten varied from .23 milligrams (mg) to more that 40 mg with each exposure. Up to 10 mg of gluten per day is generally considered a safe level of gluten consumption for most people with celiac disease, according to the University of Chicago Celiac Disease Center.

The Doggie Bag study is being done by researchers from Boston Children’s Hospital, the University of Manitoba, Beth Israel Deaconess Medical Center and Biomedal, the Spanish company that developed the stool and urine tests.

Preliminary results “confirm the general concern that a strictly gluten-free diet is difficult to achieve even by highly motivated and educated celiac disease patients,” Jocelyn Silvester, M.D., a study author and director of research of the Celiac Disease Program at Boston Children’s Hospital, said in a presentation at the recent Digestive Disease Week.

Test results

Participants in the study were recruited from the Manitoba Celiac Disease Cohort and were all due to have a follow-up intestinal biopsy as they approached the two-year anniversay of having been diagnosed with celiac disease. In the 10 days before the biopsy, they each collected three urine samples and at least four stool samples. During the first seven days, study participants also saved one-quarter of any cooked or processed food they consumed. All the samples were sent to scientists working on the study.

Interestingly, researchers found that study participants were a little more reluctant to give up the quarter servings of items they had ordered in a restaurant compared to other types of gluten-free food.

Testing for gluten peptides found positive results in 6 percent of 519 urine samples, 11 percent of 72 stool samples and 8 percent of 318 food samples.

Nearly half of the 25 food samples that tested positive for gluten had more than 20 parts per million (ppm). Five samples had more than 100 ppm. Gluten-free food labeling regulations in the United States and Canada limit the amount of gluten in packaged food labeled gluten-free to less than 20 ppm. Gluten-free food served in restaurants is not bound by the 20 ppm cut off, but restaurants are encouraged to voluntarily meet the standard. 

When food tested positive for gluten peptides, it was associated with a positive urine test in 40 percent of cases and with a positive stool test in 83 percent of cases. Stool tests are more sensitive, detecting smaller amounts of gluten. It takes more gluten to trigger a positive urine test result.  

Read more: At-home urine and stool tests available for celiac disease patients

As researchers work on final results, they are looking at the association between evident gluten exposure, the results of anti-tissue transglutaminase (tTG) blood tests and intestinal damage shown through biopsies.  The tTG test, which measures antibodies to gluten, is used to diagnose and then manage celiac disease. A biopsy that shows damage to the absorbing lining of the intestine is the gold standard for celiac disease diagnosis. 

The relationship between how much gluten someone with celiac disease consumes while on the gluten-free diet and biopsy and blood test results is unclear and scientists are interested in learning more. Early results of the Doggie Bag study show no clear associaton between documented gluten exposure and persistent damage to the villi that line the intestine, called villous atrophy. 

For example, two study participants had no indication of gluten in the food they ate or in stool or urine. One had improved biopsy results, but the other did not. Meanwhile, two participants who consumed food containing more than 100 ppm of gluten showed improvement on their biopsies. 

Read more: Test shows celiac disease patients are regularly exposed to gluten

The role of stool and urine tests

The Doggie Bag study concludes that more research is also needed to clarify the role of GIP urine and stool testing in the management of patients with celiac disease. 

The tests are a newer tool being used by scientists to get definitive evidence of how much gluten patients are actually consuming. This is one of the first studies to look at gluten in food and consequent gluten in stool and urine, as well as related blood tests and biopsies. 

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