Is sharing a toaster safe for people with celiac disease?

October 9, 2019

Study questions whether separate toasters, pots and utensils are really necessary

By Amy Ratner, Medical and Science News Analyst

When she was first diagnosed with celiac disease, Stephanie Bostwick shared her kitchen and her toaster with a gluten-eating partner and found she was often sick despite keeping everything very clean. Now, she has her own dedicated gluten-free kitchen.

Debbie Benson’s family has a separate toaster in a separate part of their kitchen to protect daughter Nora, who has celiac disease, from cross-contact with gluten.

Researchers from the Celiac Disease Program at Children’s National Health System and the Harvard Celiac Disease Program had celiac disease patients like these in mind when they did a recent study that investigated whether a separate toaster and other kitchen items are needed.

Gluten cross-contact

Based on test results of gluten-free bread toasted in a shared toaster, pasta cooked in a shared pot and cupcakes cut with a shared knife, the study found that gluten cross-contact is rare in these cases.

“Some kitchen activities may pose less of a risk of cross-contact with gluten than is commonly believed,” the study authors wrote. Additionally, risk is easily reduced by washing kitchen items with water, the study said. Researchers noted that current recommendations about using dedicated kitchen utensils, pots and toasters are based on expert consensus “with scant data to support them.” So, they set out quantify the real risk.

But neither Bostwick nor Benson, both members of the Beyond Celiac patient and family advisory council, plan to change their kitchen habits based on the study results. Bostwick said the testing methods don’t seem thorough enough to ensure safety for celiac disease patients.

Other celiac disease patients voiced the same concerns about the study on social media. Several food testing experts also weighed in on social media, noting that more than one portion of each food sample should have been tested to be sure measure of gluten content was reliable.

“I’ve been glutened by cross-contact previously and the study doesn’t make me feel any safer about sharing a toaster,” Bostwick said.

Benson said the not enough samples were tested to put the family’s mind at ease that toast made in a shared toaster would be safe every time. But she added that the study clarifies what is safe, to a point. In particular she was interested to see that none of the 20 samples of bread toasted in a shared toasted were found to contain more than 20 parts per million of gluten, the cutoff for foods labeled gluten-free.

Study limitations noted by the authors include the small number of samples tested and use of tests that do not detect hydrolyzed gluten.

“We still recommend following all guidelines from your celiac care team to prevent cross contamination while we do further study,” said Benny Kerzner, MD, senior author and director of National Hospital’s celiac program. “But the results are compelling enough that it’s time for our larger celiac community to look at the current recommendations with a critical eye and apply evidence-based approaches to pinpoint the true risks for families and eliminate some of the hypervigilant lifestyle changes that we sometimes see after a family receives a celiac [disease] diagnosis.”

People with celiac disease have different ways of controlling cross-contact at home, with varying degrees of separation. Some keep a completely gluten-free kitchen. Others have designated areas for gluten-free food preparation and storage. Some use dedicated toasters, utensils and pots while others share spaces and kitchen items but keep them clean to prevent cross-contact with gluten. Toaster bags, made from food-grade Teflon, are also used to keep gluten-containing crumbs off of gluten-free bread in a shared toaster.

Testing toasters, pots and knives

In the study, gluten-free toast was made in a toaster previously used for whole wheat bread. Gluten-free cupcakes were sliced with a knife used to cut gluten-containing cupcakes. Gluten-free pasta was cooked in a pot in which wheat-based pasta had been prepared.

In all cases, the gluten-free items tested to contain less than 20 parts per million of gluten, in most cases less than half that, the study found. Less than 20 ppm is considered a safe standard for food labeled gluten free in the United States and Europe. The only time significant gluten cross-contact was found was when gluten-free pasta was cooked in water that had previously been used to cook wheat-based pasta.

Twenty pieces of gluten-free bread were toasted in a shared pop-up toaster. None had a detectable amount of gluten when a test sensitive to less than 5 parts per million of gluten was used.  When toast was made in shared rolling toaster, the type commonly found in cafeterias and restaurants, 16 of 20 had no detectable gluten, while four had between 5 and 10 ppm, still far lower than the less than 20 ppm standard used for gluten-free labeling.

“Surprisingly, the gluten transfer when using a shared toaster was minimal, even with visible accumulation of gluten-containing crumbs in the toaster pan,” the study authors wrote.

Twelve samples of gluten-free pasta cooked in either a pot that had previously been used to cook gluten-containing pasta and then rinsed in water or washed with soap and water had no detectable gluten.

When gluten-free pasta was cooked in water that had previously been used to cook gluten-containing pasta, a practice that has reportedly been used in some restaurants, all 12 samples had more than 20 ppm. Test results ranged from about 39 ppm to 116 ppm. When the samples were rinsed under running water, the gluten content dropped to less than 20 ppm.

Thirty gluten-free cupcakes were sliced with a knife that had been used to cut a gluten-containing cupcake. Only two were found to contain more than 20 ppm. When the knife was washed, 28 had no detectable gluten and two had less than 20 ppm.

Consequently, the study concludes that broader investigation is needed to provide evidence about food preparation practices that “balance the risk of gluten exposure with harm from anxiety and hypervigilance.” Study authors advise celiac disease patients and parents of children with celiac disease to continue to ask questions about how food they eat outside the home is prepared.

The study was presented at the recent International Celiac Disease Symposium and published in the journal Gastroenterology.

Concerns remain

“Anyone who has celiac disease knows the pain associated with ‘getting glutened,’” said Bostwick. “That is why people are willing to take every precaution, to the point of adding undue stress and anxiety to their lives.” In addition to continuing to use a dedicated toaster, she also plans to keep using a dedicated pot to cook pasta and to use separate utensils.

“I feel safe using a knife that has been thoroughly cleaned, and I wouldn’t try to use a contaminated knife,” she explained. “Otherwise, I will pass on eating the cupcake.”

Benson agreed that using a shared knife does not seem like a safe practice because she could not be 100 percent sure gluten cross-contact would never occur. “The study results are intriguing,” she said.  “But I will continue to stick with our current food prep for our daughter. I think more proof is necessary to convince me to change preparation methods.”

You can read the study here.

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