Students are choosing healthier school lunches, thanks to a federal program that updated nutrition standards, a University of Washington School of Public Health study has found.

The study, published online Jan. 4 in JAMA Pediatrics, evaluated the Healthy Hunger-Free Kids Act, passed by Congress to foster a healthy school environment and promote lifelong healthy eating behaviors. The new standards took effect in 2012 and increased access to whole grains, vegetables and fruits.

“The study found that the nutritional quality of school meals improved after the new requirements went into effect,” said lead author Donna Johnson, professor of health services and associate director of the School’s Center for Public Health Nutrition. “Nutritional quality, in terms of vitamins, minerals and fiber, increased and the calories per gram decreased.”

Researchers examined the quality of meals at three middle schools and three high schools in the Renton School District in the Seattle area beginning in January 2011 (16 months before the regulations took effect) until January 2014 (15 months after they began). Amounts of calcium, vitamins A and C, iron, fiber and protein were calculated using daily school food production records provided by school food service managers.

The overall nutritional quality of the meals chosen by students improved by 29 percent, researchers found, while the calorie content per gram dropped by 13 percent.

“This study included more than 1.7 million meals over three school years and is the largest and longest study to date to measure the impact of the new school meal regulations that went into effect in 2012,” Johnson said.

She noted the study was done in a racially, ethnically and economically diverse school district. “That indicates that many different kinds of students can benefit from the improvements to school meals,” Johnson said.

“In concert with other recent studies that have found that students are actually eating these healthier foods, this study contributes to a growing body of evidence that indicates that the changes to school meal policies are working as intended to improve children’s diets,” Johnson added. “The improvements to the nutritional quality of school lunches impact the health of millions of children each day in the US.”

Researchers said the new nutrition standards did not affect school lunch participation, with 47 percent of students taking part in school meals before the standards took effect and 46 percent participating afterward. The study did not determine actual consumption of food.

Co-authors were Mary Podrabsky, Anita Rocha and Jennifer Otten.