By Dr. Mallika Marshall

BOSTON (CBS) – While going gluten free has become a popular fad, for patients with celiac disease, even small amounts of gluten in their diet can make them sick. But a new study from Columbia University finds that many so-called gluten-free offerings at restaurants are not, in fact, free of gluten.

More than 800 people around the country used a portable device to determine the presence of gluten in foods served at restaurants. Gluten was detected in almost a third of foods labeled “gluten free”, but was present in more than half of all gluten-free pizzas and pastas. Interestingly, restaurant foods were more likely to test positive in the northeast than in the west.

Researchers urge some caution because the device is highly sensitive and can detect tiny levels of gluten, well below the minimum levels for a product to be labeled gluten free.

But they say cross-contamination could occur if, for example, a gluten free pizza is cooked in the same oven as a regular pizza or if gluten free pasta is cooked in the same water as regular pasta. Food preparers may need to be better educated on how to handle gluten-free products.

Dr. Mallika Marshall