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If you've been to a restaurant in the last few years, you’ve likely seen the words gluten-free 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 non-celiac gluten sensitivity.

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