At last count, 28 percent of adults said they were gluten-free, or something close to it; the U.S. market for gluten-free foods has grown to more than $4 billion. And yet, as anyone who’s ever wondered whether there’s really gluten in oats can tell you, there hasn’t been an official definition of what, exactly, qualifies a food as gluten-free. Now there is one, courtesy of the Food and Drug Administration.

Starting on Aug. 5, packaged foods will be officially considered gluten-free if they contain fewer than 20 parts of the protein per million per kilogram, an amount that even people with celiac disease can tolerate—and the smallest quantity that can be reliably measured. With all the hype and its inevitable debunking, naturally I was suspicious of some gluten-free claims. But the FDA says 95 percent of food labeled gluten-free meets the criteria.

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