OMAHA, Neb. (AP) - The nation's largest microwave popcorn maker, ConAgra Foods Inc., 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 Omaha-based company decided to remove the chemical diacetyl from its popcorn because of the risk it presents to workers who handle large quantities.

Diacetyl has been linked to cases of a rare life-threatening disease often called popcorn lung.

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

On Tuesday, a pulmonary specialist at Denver's National Jewish Medical and Research Center, Dr. Cecile Rose, said he has 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.