It's not hard to buy gluten-free foods—a wide range of products are on the market, from doughnuts to communion wafers—but it can be hard for consumers to know exactly what they're getting. Now, they can expect any food bearing the label "gluten-free" to adhere to the same standard, thanks to new rules released by the U.S. Food and Drug Administration.

Gluten, the protein found in wheat, barley, rye, and other select grains, has become an increasingly unwelcome guest at the table in recent decades. And it's not just because of a "made-up allergy that you invented to get attention," as a skit on Saturday Night Live purported.

Three million Americans, about one percent of the population, suffer from an autoimmune disorder called celiac disease. In people with celiac disease, even the smallest trace of gluten can trigger the production of antibodies that damage the lining of the small intestine. The condition poses a host of health risks including osteoporosis, infertility, and intestinal cancers.

Until last Friday, no standard definition for the term "gluten-free" existed—even though the market for gluten-free food and beverages reached $4.2 billion in 2012. The "gluten-free" label slapped onto products "was in good faith," says Celiac Disease Foundation CEO Marilyn G. Geller. "You spent a lot of time in grocery stores hoping that the company labeling products 'gluten-free' was adhering to a voluntary standard."

To comply with the FDA's new rules, products labeled "gluten-free" must contain less than 20 parts per million of the protein—or about an eighth of a teaspoon of flour in 18 slices of gluten-free bread. That's low enough for most people who have mild to severe gluten allergies.

Tastes Great, Less Worry

The regulation comes almost a decade after the FDA began requiring food packaging to list wheat and other major allergens under the Food Allergen Labeling and Consumer Protection Act of 2004.

"Many people think that developing a labeling rule is an easy thing to do, but a lot goes into it," says Felicia Billingslea, the FDA's director of food labeling and standards. Years were devoted to researching a safe threshold for consumers with celiac disease. "We have a standard definition now, and it's consistent internationally with Canada and the E.U."

The rules also ensure that companies can't label products "gluten-free" if they could be cross-contaminated by other foods processed at the same facility. Manufacturers have until August 5, 2014, to comply.

Some terms on food packaging may still confuse consumers—"organic" versus "all-natural," "cage-free" versus "free-range." But the "gluten-free" label now stands to ease the minds of millions suffering from serious food allergies.