The Healthy Hunger-Free Kids Act (HHFKA), which was approved in 2010 and took effect in 2012, revised the standards for school lunches in order to provide children healthier meals — and the new rules are having a positive impact on children's health, according to a new study published online Jan. 4 in JAMA Pediatrics.

The HHFKA mandated schools to make whole grains, vegetables and fruits more available to students and to improve the quality of all school foods, including those in vending machines. With the National School Lunch Program catering to more than 30 million students, the HHFKA was expected to affect children's health.

The researchers investigated the nutritonal quality of children's meals before and after HHFKA implementation. They analyzed data from three middle and three high schools in Washington, studying students' food choices for more than 1.7 million lunches from 2011 to 2014.

"We found that the implementation of the new meal standards was associated with the improved nutritional quality of meals selected by students," wrote the authors, according to a press release. "These changes appeared to be driven primarily by the increase in variety, portion size and the number of servings of fruits and vegetables."

The researchers also calculated the energy density of foods and the mean adequacy ration (MAR) for vitamin C, vitamin A, calcium, protein, iron and fiber. They found that MAR increased from 58.7 before HHFKA implementation to 75.6 after HHFKA implementation. Energy density decreased from 1.65 to 1.44, indicating that the meals had lower calories since the regulations took effect.

However, the School Nutrition Association, in a letter addressed to Congress in October, said the new regulations have forced "local school districts to absorb $1.2 billion in additional food and labor costs" in 2015 alone.

Erin R. Hager, from the University of Maryland School of Medicine, and Lindsey Turner, from Boise State University, appealed that policy makers focus on "the successes of the HHFKA, rather than abandoning the recent progress made in keeping our nation's children healthy."

"The HHFKA created significant improvements in school nutrition, but that progress is now at risk of repeal.... We encourage policy makers to consider the hard evidence rather than anecdotal reports when evaluating the impact of policy changes," they wrote in an editorial.