Large U.S. fast food chain restaurants that offer primarily high-calorie foods have been adding healthier options to the menu.

These new items contain an average of 60 fewer calories than typical menu selections in 2012, John Hopkins Bloomberg School of Public Health reported. The researchers hope these changes will trigger an overall change in the U.S; a 12 percent reduction in calories in this industry could also have a significant impact on the nation's obesity epidemic.

Past studies have shown about 33 percent of young children, 41 percent of adolescents, and 36 percent of adults eat at fast food restaurants.

"If the average number of calories consumed at each visit was reduced by approximately 60 calories -- the average decline we observed in newly introduced menus in our study -- the impact on obesity could be significant," said Sara N. Bleich, PhD, an associate professor in the Department of Health Policy and Management at the Bloomberg School, and lead author of the study.

To make their findings researchers used data from MenuStat and looked at the options in 66 of the 100 largest U.S. restaurant chains. Between 2012 and 2013 a number of lower calorie items were added to menu sections such as the main course, beverages and children's menus. Typically unhealthy items such as burgers and pizza did not show a reduction in calories.

"You can't prohibit people from eating fast food, but offering consumers lower calorie options at chain restaurants may help reduce caloric intake without asking the individual to change their behavior - a very difficult thing to do," Bleich said.

"Given that the federal menu-labeling provisions outlined in the 2010 Affordable Care Act are not yet in effect, this voluntary action by large chain restaurants to offer lower calorie menu options may indicate a trend toward increased transparency of nutritional information, which could have a significant impact on obesity and the public's health," she concluded.

The findings were published in the October issue of the Journal of Preventative Medicine.