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Is That Gluten-Free Diet Really Gluten-Free?

By Carrie Dennett, MPH, RDN, CD

Dietitians who counsel patients with celiac disease know that adhering to the only known treatment—a gluten-free diet for life—is a difficult, even daunting, proposition. It’s hard enough to say goodbye to obvious sources of gluten—bread, pasta, and other products made from wheat, rye, or barley—but it’s even more challenging to constantly scrutinize food labels to sleuth out “hidden” sources of gluten, such as fillers and thickeners in some prepared foods.

A typical adult without celiac disease consumes 5 to 15 g of gluten per day. Research has found that the likely safe gluten intake level for those with celiac disease is less than 10 mg per day, because that level is unlikely to cause intestinal damage in most patients,1 while recurrence of symptoms has been reported after as few as 50 mg per day. However, a meta-analysis published in February in The American Journal of Clinical Nutrition found that celiac patients are, on average, inadvertently consuming nearly five times that amount: 244 mg/day, based on urine and stool samples.2 That’s easily enough to trigger symptoms and enable intestinal damage to continue.

Inadvertent — or Intentional?
Approximately 20% of patients with celiac disease experience what’s known as nonresponsive or refractory celiac disease. Despite reporting adherence to a gluten-free diet for more than 12 months, they experience persistent signs and symptoms, including ongoing atrophy of the villi—the small, fingerlike projections that line the intestinal walls, greatly increasing the absorptive surface area.3

However, a 2016 study in Journal of Clinical Gastroenterology found that while some “nonresponsive” celiac patients had been incorrectly diagnosed with celiac disease—instead having conditions unrelated to gluten—among nonresponsive patients with confirmed celiac diagnoses, continued exposure to gluten was the main cause of persistent symptoms. These symptoms cleared up in 63% of those patients after further dietary modification.4

A 2017 study in the journal Gut measured urine levels of gluten immunogenic peptides (GIPs) in 76 healthy subjects and 58 patients with celiac disease.3 All of the patients with celiac disease in the study reported complete adherence to a gluten-free diet, but their urine told a different story. The researchers found that 89% of patients with celiac disease who had healthy intestinal villi also had no detectible GIP levels, while all patients with atrophy of the villi had detectible GIP levels.

Barriers to Avoiding Gluten
There are many obstacles to total avoidance of gluten.5 Cross-contamination is a concern for anyone who dines out or shares a kitchen with people who aren’t following a gluten-free diet. Gluten-free diets can stress a modest food budget. Patients may become weary from constantly reading labels and quizzing restaurant wait staff. It isn’t uncommon for some patients with celiac disease to act on the impulse to take an occasional “vacation” from their diet, especially when on vacation or at social gatherings.

Knowledge about which foods contain gluten is another reason for consumption of gluten despite self-reported adherence to a gluten-free diet. A 2016 study published in Nutrition found that many individuals who think they’re following a gluten-free diet can’t correctly identify gluten-free foods.6 Of the study’s 82 participants—who’d been following a gluten-free diet for an average of six years—more than one-half reported strict adherence, while 18% reported intentional gluten consumption and 21% acknowledged rare unintentional gluten consumption. The participants were given a list of 17 common foods and asked to identify which contained gluten, which didn’t contain gluten, and which were questionable. No participant correctly labeled all 17 foods, and only 30% identified at least 14 foods correctly. The scores didn’t correlate with self-reporting of degree of adherence.

The survey also asked participants about where they received their information on gluten-free diets. Cookbooks, advocacy groups, and print media were the most commonly used sources. While more than 80% of participants said they received information from a dietitian, less than 70% said that information was useful. The authors didn’t expand on that information, but it’s possible that some celiac patients aren’t referred to a dietitian who specializes in the complexities of achieving a 100% gluten-free diet.

Future Directions
The pursuit of vaccines or drug therapies to provide treatment alternatives to a gluten-free diet continues.7,8 In the Gut study, the subjects with severe lesions in their intestinal mucosa didn’t necessarily test positive in blood tests for antitissue transglutaminase or antigliadin antibodies, suggesting that these tests aren’t a good measure of monitoring adherence to a gluten-free diet.3 Although more research is needed to confirm clinical applicability, it may be that urine testing is a superior—and less invasive—method of helping patients avoid the consequences of unintended gluten consumption.

— Carrie Dennett, MPH, RDN, CD, is the nutrition columnist for The Seattle Times and speaks frequently on nutrition-related topics. She also provides nutrition counseling via the Menu for Change program in Seattle.


1. Akobeng AK, Thomas AG. Systematic review: tolerable amount of gluten for people with coeliac disease. Aliment Pharmacol Ther. 2008;27(11):1044-1052.

2. Syage JA, Kelly CP, Dickason MA, et al. Determination of gluten consumption in celiac disease patients on a gluten-free diet. Am J Clin Nutr. 2018;107(2):201-207.

3. Moreno M de L, Cebolla Á, Muñoz-Suano A, et al. Detection of gluten immunogenic peptides in the urine of patients with coeliac disease reveals transgressions in the gluten-free diet and incomplete mucosal healing. Gut. 2017;66(2):250-257.

4. Stasi E, Marafini I, Caruso R, et al. Frequency and cause of persistent symptoms in celiac disease patients on a long-term gluten-free diet. J Clin Gastroenterol. 2016;50(3):239-243.

5. Sainsbury K, Halmos EP, Knowles S, Mullan B, Tye-Din JA. Maintenance of a gluten free diet in coeliac disease: the roles of self-regulation, habit, psychological resources, motivation, support, and goal priority. Appetite. 2018;125:356-366.

6. Silvester JA, Weiten D, Graff LA, Walker JR, Duerksen DR. Is it gluten-free? Relationship between self-reported gluten-free diet adherence and knowledge of gluten content of foods. Nutrition. 2016;32(7-8):777-783.

7. Haridy J, Lewis D, Newnham ED. Investigational drug therapies for coeliac disease — where to from here? Expert Opin Investig Drugs. 2018;27(3):225-233.

8. Kurada S, Yadav A, Leffler DA. Current and novel therapeutic strategies in celiac disease. Expert Rev Clin Pharmacol. 2016;9(9):1211-1223.