Is Any Amount of Gluten Safe for Those with Celiac Disease?

Celiac Disease is essentially an autoimmune disorder that is triggered by eating foods containing gluten, which is in wheat, rye, and barley products. While there are blood tests to detect the disease, the true confirmation of the diagnosis requires doing a biopsy of several sites in the small bowel. If the villi in the small bowel show damage, the diagnosis is confirmed.

The only treatment for Celiac Disease is to avoid gluten in the diet. While it's obvious that those with Celiac Disease need to avoid almost all bread products, newly-diagnosed patients are also taught to recognize the "hidden" gluten in many commercially prepared foods. Even restaurant or home-cooked meals that are (presumably) prepared fresh from gluten-free products are considered suspect if they are prepared in a kitchen that also contains gluten products due to the risk of cross-contamination: a cooking utensil could carry gluten molecules from a food containing gluten to an otherwise gluten-free food.

To avoid that risk, many of those with Celiac Disease are extremely cautious about eating in restaurants or kitchens not their own and will often prepare and take their own food when dining with friends or family. This is reasonable, given that the prevailing teaching is that products with "more than 20 parts per million (ppm) of gluten" will cause damage to their small intestine.

The problem, however, is that there's little proof that such microscopic amounts will actually cause damage. In 2007, researchers in Italy (Am J Clin Nutr 2007; 85:160-6) sought to establish how much, if any, gluten could be tolerated in those with Celiac Disease.

They recruited 39 otherwise healthy men and women between the ages of 19 and 55 who had previously been diagnosed with Celiac Disease and had been following a Gluten-Free Diet for at least two years. For thirty days the participants followed an especially strict Gluten-Free Diet, avoiding restaurant meals and only eating certified gluten-free products. (The Italian government requires that certified gluten-free products contain less than 20ppm of gluten.) After this first month, they were given the standard tests given to diagnose Celiac Disease: a blood antibody test as well as a small bowel biopsy.

After this baseline was established the subjects were randomly assigned to take one of three pills daily for the next 90 days: a pill containing 10mg of purified gluten, a pill containing 50mg of purified gluten, or a placebo containing 50mg of purified cornstarch. At the completion of the 90 day trial the standard antibody and small bowel biopsy tests were repeated, and the results for each subject compared to the baseline tests.

Somewhat surprisingly, the antibody tests for all subjects, whether they were taking placebo, 10mg/day or 50mg/day, remained within the normal range. One would expect that the villi in the small bowel would show signs of damage for those taking the gluten pills, yet the researchers actually found evidence of improvement in the villi for 11 of 13 people in the placebo group. On the other hand, 7 of 13 in the 10mg/day group showed any damage to their villi, and 11 of the 13 people in the 50mg/day group also showed some damage.

People's sensitivity to gluten varies quite a bit, but it seems clear that 50mg gluten per day is sufficient to cause damage to the villi in most people. Only half the people in the 10mg/day group showed damage, however, which led the researchers to conclude that while 50mg/day was too much, 10mg/day "remains a gray area." A person with Celiac Disease would have to eat 16.67 pieces of gluten-free bread (actually containing 20ppm of gluten) to ingest 10mg of gluten. (For reference, a typical 30g piece of bread contains 4.8g [4800mg] of gluten.)

What this means for you

This study should provide some reassurance to those with Celiac Disease who are so concerned about gluten contamination that they almost never eat foods made outside their own home. It's clear that the minute amounts of gluten that might be found in foods that are prepared with due concern for avoiding obvious contamination, whether made in a restaurant or in someone's home, are unlikely to cause any damage to the small intestine of those with Celiac Disease.

First posted: March 20, 2010