"Students who participate in the school lunch program tend to be more obese in general, not because of the program itself but because they usually come from lower-income households where obesity is more of a problem," explained study author Daniel Taber, a research scientist with the Health Policy Center of the Institute for Health Research and Policy at the University of Illinois at Chicago.
"So, what we looked at was a state-by-state comparison of the gap in obesity between those kids who participate in the school lunch program and those who don't," Taber said. "And what we saw was that the gap was smaller in states that exceeded the USDA [U.S. Department of Agriculture] standard."
Taber and his colleagues report their findings online April 8 in the journal JAMA Pediatrics.
First established in 1946, U.S. National School Lunch Program (NSLP) meals are now consumed daily by about 32 million schoolchildren across the United States. Participation is offered to those from households where income levels are low enough to qualify.
Although lauded for its intent, the federally funded program is administered at the state -- rather than federal -- level, and it has faced criticism for often not meeting current USDA nutritional standards.
To explore the effect of any differences, the team took a snapshot of nearly 4,900 eighth-grade students across 40 states in 2006-2007.
Body mass index (or BMI, a measurement based on height and weight) and obesity data on the students was gleaned from a national study launched in 1998 to track a nationally representative sample of school kids.
Some of the kids got free or discounted NSLP lunches; some purchased food at school at market rates; and some got their lunches from home or elsewhere.
The investigators found that in states where USDA nutritional standards were exceeded, just about 21 percent of the NSLP children were found to be obese, compared with a little more than 17 percent of non-NSLP children.
However, that spread was much wider in states serving at-standard meals, with 26 percent of NSLP kids deemed obese compared with just under 14 percent of non-NSLP students. Similarly, BMI gaps were also greater in states where minimum standard meals were offered.
What's more, the researchers found that students consuming healthier meals were not more likely to seek other sources (such as vending machines or fast-food establishments) for less nutritional sweet or salty foods and/or sugary drinks.
That said, Taber said that going forward there is reason to be optimistic, given that states are now in the process of updating the NSLP laws that had been place when the study was conducted to more closely match updated USDA standards. The newer standards place a greater emphasis on the importance of preparing meals that include whole grains, fruits, vegetables and skim milk, while cutting back on trans fats.
"What this means is that what had been above-standard during our study will now be standard," he noted. "So, essentially those states that had been providing meals that exceeded previous USDA standards were ahead of the curve. And they saw benefits as a result, as opposed to those states that only met outdated minimums, and therefore missed an opportunity to lower obesity risk."
In an accompanying editorial, Marion Nestle, a professor in the department of nutrition, food studies and public health at New York University in New York City, said the findings are important because they highlight the government's key role in "leveling the playing field," so that all children are exposed to quality nutrition rather than junk food.
"The food industry cannot make significant changes on its own because food companies are beholden to stockholders' concerns about returns to investors," she said. "Consumer demand also doesn't work in the face of millions of dollars spent on food marketing, advertising and lobbying," Nestle pointed out.
"[But] if you take junk food and sodas out of schools, kids don't eat as much of them and are healthier," Nestle said. "If you have strict nutrition standards for school food, the food is healthier and so are the kids. This may seem self-evident, but now we have research to prove it."
For more on the U.S. National School Lunch Program, visit the U.S. Food and Nutrition Service.