Gluten-free eating has exploded in America, but scientists aren't sure how many people are doing it for medical reasons.
A study released Tuesday suggests that nearly 2 million U.S. adults have celiac disease, a digestive disorder caused by foods that contain gluten, a protein that is in wheat.
In the past few years, scientists have also identified another group of people as "gluten sensitive" -- a different condition with similar symptoms.
But there is no test for gluten sensitivity, and how many people actually have it is a matter of debate.
Meanwhile, gluten-free has become a fad. Americans will spend an estimated $7 billion this year on foods labeled gluten-free, according to the market research firm Mintel.
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