By Amy E. Feldman

PHILADELPHIA (CBS) –Gluten is a substance found in grains like wheat, barley and rye, and it’s what gives bread and other food products their chewy, delicious quality. Mmmm. Bread.

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With increasing numbers of people diagnosed with celiac disease, an inability to process gluten, and an even greater number of people who have decided to eliminate gluten for weight loss, the market for foods that contain no gluten has skyrocketed. Americans now spend over 4.2 billion dollars on foods that don’t contain gluten.

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Until recently, the standard for ‘gluten free’ was up to manufacturers, but now the FDA has provided guidance.

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In order to be labeled gluten free, a product must have less than 20 parts per million of gluten, a level low enough that it won’t cause a health reaction for most people with celiac. While it is good news for consumers that labels have a standard meaning, the definition isn’t exactly self-explanatory to most people: 20 parts per million?? What? So, if you don’t understand the label or the benefits of a fad diet, ask your doctor.