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If you've been to a restaurant in the last few years, you’ve likely seen the words glutenfree written somewhere on the menu. But what exactly is gluten, and why can’t some people process it? And why does it only seem to be a problem recently? William D. Chey unravels the facts behind celiac disease, wheat allergies and nonceliac gluten sensitivity.

Lesson by William D. Chey, animation by Stretch Films, Inc.