(CNN) Ever since new meal standards went into effect in schools across the United States in 2012, experts have worried that the changes would result in fewer students eating school lunches. A new study of a Washington state school district suggests this has not been the case.
The meal standards, which are part of the United States Department of Agriculture Healthy, Hunger-Free Kids Act of 2010, made sweeping changes to the breakfasts and lunches served at U.S. schools. They put a cap on the number of calories per meal and required that meals contain at least one serving of fruits and vegetables.
Researchers examined the impact of these changes at three middle schools and three high schools in an urban, racially diverse Washington state school district that enrolls about 7,200 students. The researchers looked at the nutritional value of lunches the schools prepared, as well as what the students selected, in the 16 months before the changes and 15 months after.
The researchers found increases in the levels of six nutrients -- calcium, vitamin A, vitamin C, iron, fiber and protein -- in the meals after the changes were introduced. (Unhealthy components such as fat and sodium were not included in the analysis.) They also found that nearly as many students in the school district participated in the meal program before the Healthy, Hunger-Free Kids Act took effect as after, 47% compared with 46%.
"This is, in my mind, really verification that implementing these changes are first of all doable," said Donna B. Johnson, professor in the School of Public Health at University of Washington and lead author of the study, which was published Monday in the journal, JAMA Pediatrics.
The other important finding is that school meal participation did not change, especially among high school students who can leave campus during lunch and buy other food, said Johnson, who is also a registered dietitian and member of the Academy of Nutrition and Dietetics. "Our thinking was, if it's going to work for these older students who have more options, that's really a powerful statement."
Johnson and her colleagues did not look at whether students actually ate the healthier lunches they chose, or if those servings of fruits and veggies ended up in the trash bin. However, they cited previous research that found that the amount of plate waste has not changed since meal changes were introduced. And if plate waste hasn't increased while portions of healthy foods have gone up, it probably means that kids are eating more of these foods, Johnson said.
The researchers found that the improvements in nutritional quality of school lunches were due mostly to the increases in portion size and variety of fruits and vegetables. These changes will hopefully inspire better eating habits among students.
"We tend to eat more if larger portions are put in front of us and if there's more variety," Johnson said. "We can use that to our advantage to nudge people along to make good choices."
There has been pushback from groups such as the School Nutrition Association, which argues that the meal changes mandated by the Healthy, Hunger-Free Kids Act has driven up costs and resulted in more food waste.
In October, the School Nutrition Association and the School Superintendents Association wrote a letter to Congress stating that school districts do not receive full reimbursement from the USDA for the increased costs associated with the new school meal standards. (The letter states that the requirements added 10 cents to the cost of a lunch and 27 cents to the cost of a breakfast, but schools were only given an additional 6 cents per lunch and no additional money for breakfasts.)
The School Nutrition Association also advocates changes that it says could improve meal participation rates, such as repealing the requirement that all grains be whole grain rich and returning to the previous requirement that only half of grains be whole grain rich.
"We commend schools that have maintained student participation in meal programs, but the JAMA study ignores the unintended consequences causing nationwide decreased participation in the National School Lunch Program," said Jean Ronnei, president of the School Nutrition Association and chief operations officer at Saint Paul Public Schools in Minnesota.
A report by the Center for Science in the Public Interest suggested, however, that the decrease in meal participation is due to factors other than the new meal requirements. The decline began in the 2007-2008 school year, before the Healthy, Hunger-Free Kids Act went into effect, and was mostly among kids who paid for lunch and not those who qualified for free lunches. Thus, the report concluded, the trend was probably driven by the Great Recession.
In response to criticism of the meal changes, Johnson said, "All I can do is come back and say our study showed it's working and it's achieving its intended purpose and millions of students every day are eating healthier meals because of it."
Erin R. Hager, assistant professor of pediatrics at University of Maryland, agrees that the new study suggests that the Healthy, Hunger-Free Kids Act is meeting its goal of making school meals healthier, and doesn't seem to be affecting how many kids are having school lunches.
"It's nice to see in such a well designed study that participation rates did not decline," said Hager, who was not involved in the research, but wrote an editorial about the study that was published in the same issue of JAMA Pediatrics.
However, it remains unclear at this point whether the findings of the current study capture what is happening in other school districts in the country with different demographics and that are more rural, Hager said.
"This is a new policy so we're just starting to see these nicely designed studies come out that show an impact or no impact [on what students are eating], and I bet we will see a lot more data in this year come out about consumption and choice," she said.