(PhysOrg.com) -- Here's some simple math for school officials and parents in the fight against childhood obesity: School lunchtimes minus snack food equals a much lighter student body. Literally.
A new study from the University of Nebraska-Lincoln has directly estimated the relationship between school food policies and students' weight by examining nutrition policies in schools and coupling it with survey information from students, parents and school administrators.
The findings suggest that a single policy shift -- banning all junk food from a la carte lines during school lunch hours -- would result in an 18 percent reduction in overweight or obese students.
With more than 30 million children being served lunch and 9.7 million being served breakfast each school day, the new evidence adds to a growing argument for beefing up U.S. school food policies when dealing with unhealthy food and drinks.
"The upward trend in the incidence of obesity among children and adolescents has gained national attention and has motivated calls for immediate action to alter environments to prevent and reduce overweight and obesity," the study says.
"The school environment plays an important role in shaping eating habits among youth as they spend one-fourth to one-third of their day at school."
The study, by UNL associate professors Patricia Kennedy (marketing) and Mary McGarvey (economics), along with Bree Dority, assistant professor of economics at the University of Nebraska at Kearney, examined survey responses from seventh- and 12th-graders and their parents at eight Midwestern schools.
Researchers then combined those responses with those of school administrators and considered a range of other factors to precisely gauge the effect of schools' food policies on students' weight.
The study suggests expanding the USDA's current ban on selling so-called Foods of Limited Nutritional Value during school meal times to include all junk food a la carte selections.
While the current USDA ban covers many unhealthy foods, it doesn't cover items like candy bars, soda, potato chips, cookies and other high-fat snack foods.
The researchers recommended that marketers of foods and beverages to children and adolescents limit or eliminate their sales of junk foods in schools, as well: "Marketers have known for some time that building long-term relationships with their consumers is much more profitable than having a constant turnover of buyers," it says.
Explore further: Study finds students are eating fruits and veggies in school lunches, contradicting criticism
More information: Their findings, which appear in the Nov. 1 edition of the Journal of Public Policy and Marketing, are from a three-year research project on child obesity funded by the U.S. Department of Agriculture.