Until this week, gluten-free labels on packaged foods had not been regulated, and manufacturers made their own decisions about what it means, according to The Associated Press.

Now, the new requirement and standard a product has to have to hold the gluten-free label will be important for people who suffer from celiac disease and don't absorb nutrients well, the AP reported.

Under a rule announced a year ago, food manufacturers had until Tuesday to ensure that anything labeled gluten-free contains less than 20 parts per million of gluten, ensuring that those products are technically free of wheat, rye and barley, according to the AP.

The standard will ensure that companies can't label products "gluten-free" if they are cross-contaminated from other products made in the same manufacturing facility, the AP reported. The rules don't apply to restaurants, but the Food and Drug Administration is encouraging them to comply.

That amount is generally recognized by the medical community to be low enough so that most people who have celiac disease won't get sick if they eat it, the AP reported.

Celiac disease causes abdominal pain, bloating and diarrhea, and people who have it can suffer weight loss, fatigue, rashes and other long-term medical problems, according to the AP. Celiac is a diagnosed illness that is more severe than gluten sensitivity, which some people self-diagnose.

Gluten-free foods have become big business in the last several years and now, millions of people are buying the foods because they say they make them feel better, even if they don't have celiac disease, the AP reported.

Alice Bast of the National Foundation for Celiac Awareness says the gluten-free trend has been good for those diagnosed with celiac because of the increased variety of options in the grocery store, but she says it also may have prompted some companies to lose focus on the people who need those foods the most, according to the AP.

The new regulations are "raising awareness that there is a disease associated with the gluten-free diet," she said, the AP reported.