Gluten Free Watchdog, with the coauthorship of our own Dietitian Advisor Trisha Lyons RD. LD., has recently published the study “Allergen Advisory Statements for Wheat: NOT a Useful Predictor of Gluten Content”.
You can read the full text of the article.
In the US, allergen advisory statements (“Made in a facility that also processes wheat” and similar) are voluntary and are not currently defined by any federal regulation.
What this study found is that products that have warning statements such as “May contain wheat” or “Made in a facility with wheat” might be without gluten and just fine to eat. On the other hand, the lack of a statement did not mean that a product was free of gluten.