If you must eat a gluten-free diet, it can be a challenge to do so in a restaurant. In research conducted by Columbia University, they found that in the restaurants they tested, about one-third of the food labeled as gluten-free, actually contained some gluten.
In this study, data was collected from restaurants in Western states and Northeastern states. A portable gluten detection device was used. Each test included date/time, food item, restaurant name and address, presence/absence of a gluten-free label, and presence/absence of gluten. They collect 5,624 tests. Gluten was detected in 27.2% occurrences at breakfast and 34.0% occurrences at dinner. Pizza and pasta labeled as gluten-free had the highest contamination readings.
According to FDA regulation, for a food to be labeled as gluten-free, it has to have <20 ppm of gluten.