"Gluten-free" now actually means gluten-free. Gluten-free labels on foods will now be required to meet certain FDA standards.

The rule was announced by the FDA a year ago informing food manufacturers that they had until Tuesday to make sure anything that is labeled gluten-free contains less than 20 parts per million of gluten. Up until this regulation was passed, gluten-free labels were unregulated.

Gluten includes wheat, rye and barley. Wheat is typically listed in the ingredients, but rye and barley are typically hidden. The amount specified by the FDA is what is generally recognized as low enough that people with celiac disease - a disease of gluten-intolerance - won't get sick from eating it.  

"The gluten-free diet for someone with celiac disease is like insulin for diabetics," said Dr. Alessio Fasano, director of the Center for Celiac Research at Massachusetts General Hospital.

The gluten-free label is voluntary, but will be regulated. Any foods that violate the new guidelines will be subject to regulatory action.

A decade ago, celiac disease was rarer, but in the last several years awareness and diagnosis of celiac has increased. Additionally, gluten-free food has become a much bigger business in the last several years.  

"A decade ago, our research determined that the prevalence of celiac disease in the United States was 1 in 133," Fasano said in a statement. "Even then it was obvious that patients could not safely manage their diet without better labeling requirements. The FDA has devoted years of work to make sure the standard issue today was safe for celiac patients. Our research supports that standard."

Celiac can affect entire families, so labeling makes it easier for people to eat and cook without worrying about problems from gluten.

If people who have celiac eat products with gluten in them, they can have symptoms such as headaches, intestinal problems and respiratory  problems.

Additionally, gluten-free diets have become trendy among people trying to eat healthy. But that may cause people to treat celiac as a much less serious issue than it is.

"For people like myself, this is a medical necessity," said Beth Hillson, president of the American Celiac Disease Association. "My diet is my medicine. This labeling rule makes it very clear cut."

However, if people suspect having a gluten intolerance, a medical diagnosis is important, and it is impossible to find the effects of gluten on someone who doesn't eat it at all.