The nation's largest microwave popcorn maker, ConAgra Foods Inc.(CAG), says it will change the recipe for its Orville Redenbacher and Act II brands over the next year to remove a flavoring chemical linked to a lung ailment in popcorn plant workers.

The decision comes a day after a doctor at a leading lung research hospital said in a warning letter to federal regulators that consumers, not just factory workers, may be in danger from fumes from buttery flavoring in microwave popcorn.

ConAgra spokeswoman Stephanie Childs said the company decided to remove the butter flavoring diacetyl from its popcorn because of the risk the chemical presents to workers who handle large quantities.

The chemical diacetyl has been linked to cases of bronchiolitis obliterans, a rare life-threatening disease often called popcorn lung.

ConAgra's announcement comes a week after another popcorn manufacturer, Weaver Popcorn Co. of Indianapolis, said it would replace the butter flavoring ingredient because of consumer concern.

ConAgra doesn't know how soon it will be able to replace diacetyl with a different butter flavoring, Childs said, but the change will be made sometime over the next year.

"We've made that decision based on the knowledge for the potential risk to our employees," Childs said.

The Omaha-based company has already been making changes at its popcorn plants over the past few years to reduce employee exposure to diacetyl, she said.

But the company doesn't believe diacetyl in popcorn represents a safety risk to consumers, Childs said.

"We're fully confident that microwave popcorn is safe for consumers in the home," she said.

It was reported Tuesday that a pulmonary specialist at Denver's National Jewish Medical and Research Center had written to federal agencies to say doctors there believe they have the first case of a consumer who developed lung disease from the fumes of microwaving popcorn several times a day for years.