When you enter any of the forty elementary schools involved in the Alberta Project Promoting active Living and healthy Eating (APPLE), it’s clear that health takes a front seat, right next to reading and mathematics.

“People love the APPLE Schools program,” says Kerry Vander Ploeg, a postdoctoral fellow at the University of Alberta's School of Public Health. “It’s really interesting to go into an APPLE School because right away when you walk in the doors of the school, you know it’s an APPLE School.”

Bulletin boards show off the latest monthly health campaigns—like “Be a Sleep Star”—promote healthy activities for kids, and tell them which fruits and vegetables are in season.

So far, the program—which was developed and tested by a professor at the University of Alberta but now runs independently—has made some progress in changing children’s behaviors.

A 2012 article in the International Journal of Behavioral Nutrition and Physical Activity found that children at the APPLE Schools ate more fruits and vegetables, consumed fewer total calories, and were more active and less likely to be obese than kids at other elementary schools. This was followed by a 2014 study in Pediatrics, which indicated that the program might even change behaviors outside of school—with kids increasing the number of steps they took both on school days and on weekends.

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Results of School Health Programs Are Mixed

While the APPLE Schools results are impressive, other researchers question whether these types of interventions can stem the rising tide of childhood obesity. Today, one-third of children and adolescents in the U.S. are overweight or obese.

“For most of the research, the most optimistic findings are that the results are mixed,” says Ashley Merryman, co-author of NurtureShock: New Thinking About Children. “In NurtureShock, we wrote about a McMaster University study that looked at 57 studies and found four had any efficacy—and those were minimal results.”

In addition, a recent study in the journal PLOS One by Swiss researchers questions whether the effects of school health interventions will last after the kids leave the program or the program ends.

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Changing Kids’ Behavior Is Difficult

One thing is clear from the numerous pilot programs that have sought to convince kids to eat more vegetables or go for a bike ride—it’s very hard to change their behavior. And that is equally true for adults.

“By and large, interventions are really hard to work,” says Merryman. “We are creatures of habit.” You can convince a child that broccoli tastes good, but getting her to choose broccoli over potato chips is another thing entirely.

Some programs may be more effective than others. The evidence seems to show that programs that include both exercise and nutrition and that span multiple years work best.

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Many Factors Lead to Childhood Obesity

The real difficulty in combating childhood obesity is that it doesn't have a single cause. Diet and exercise are the most well-known risk factors for obesity, but genetics and environment play a big part, too. So does getting enough sleep—something many kids don’t do.

“I think a lot of the kids who are obese probably have six or seven—if not 20 million—different things that are all combining,” says Merryman, “and rarely have the interventions to date gotten at all of them.”

Recent research also suggests that children may be well on their way to obesity before they even set foot in kindergarten. A study in the New England Journal of Medicine found that kids who were overweight by age five were four times more likely to be obese in the eighth grade, compared to normal-weight children. Heavier birth weight also seemed to increase the risk of obesity later in life.

All Hands on Deck

Given the complexity of childhood obesity, Merryman says we need a comprehensive approach, which means “realizing that the kid’s environment extends beyond the school, and realizing that if you want to do something, you’ve actually got to get the parents involved, too,” she says.

The APPLE Schools program already does that, involving school staff, students, parents, and local community members in promoting healthy lifestyles for the kids. But since obesity begins early in life, program staff may need to think about interventions for preschoolers and even pregnant women.

Though study results have been mixed, Merryman says it's no time to give up. “I don’t think any researcher would say don’t have exercise, don’t have kids run around,” she says. Eating healthy and being physically active have benefits beyond preventing obesity, including reducing the risk of heart disease, diabetes, and stroke.

The challenge for researchers, then, is to figure out what is most effective in the fight against childhood obesity—and letting go of what isn't.

“It would be terrible,” says Merryman, “if a program that had mixed success, or no success, wasn’t replaced with something that we actually figured out worked.”

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