A McDonald's restaurant is pictured in Encinitas, California September 9, 2014. REUTERS/Mike Blake

(Reuters) - McDonald's Corp MCD.N said it is testing new recipes for its staple Chicken McNuggets snack in some U.S. markets to cater to growing consumer demand for healthier food.

The company said on Wednesday it started testing a “simpler” recipe for the snack in 140 restaurants in Oregon and Washington state last month.

McDonald’s did not detail the specific ingredients in the new nuggets, but said it was a recipe “parents can feel good about.”

The nuggets being tested in Portland do not contain any artificial preservatives, the company said in an emailed statement.

McDonald’s also did not say whether it would roll out the new recipes nationally.

The news, which was first reported by Crain’s Chicago Business, follows McDonald’s announcement last year that it would phase out human antibiotics from its chicken supply in the United States within the next two years.