A new survey in The Journal of the American Dietetic Association found gluten-free grains still had traces of the protein.
The contamination may occur when oats, millet and rice are grown or processed near grains with the protein, which can cause problems for people with celiac disease and other disorders who can have immune reactions to the protein.
The study is too small to give a really good idea of just how common this is, but researchers say it's a red flag that should alert companies to do extra testing of their products.
