Why Heavy Teens May Eat Less But Weigh More Than Their Thinner Peers

It may be more important than we thought to tackle obesity in childhood. A new study published in Pediatrics finds that overweight teenagers eat fewer calories than their healthy weight peers.

That’s right — they eat less. But because they also exercise less, they may be setting unhealthy lifelong patterns.

How much less? The study found that among 12- to 14-year-olds, obese girls consumed 110 fewer calories daily than healthy-weight girls. And overweight boys between the ages of 15 and 17 consumed about 375 fewer calories a day than healthy-weight boys.

Up to the ages of of 8 or 9, overweight children ate more calories than their slimmer peers. But at that age, kids of all weights are likely to be running around, playing sports and being outside. Then, as the tween years set in, some kids get into more sedentary pursuits, like video games. And, “at about age nine or ten, we start to see, essentially, a flip,” explains Skinner. Basically, heavier older kids start to eat less.

“One reason this makes sense is because we know overweight children are less active than healthy weight kids,” explains lead researcher Asheley Cockrell Skinner, Ph.D. of The University of N. Carolina.

And obesity expert Matthew Gillman of Harvard Medical School says the amount of physical activity kids participate in is key. “When you’re less physically active, you actually need fewer calories to maintain your weight,” he explains.

But if that weight’s already higher than it should be, that could signal the beginning of a long-term problem.

“Once you become overweight there are changes in your body that make you different from someone who’s not (overweight) ” explains Sophia Yen of Stanford Medical School. “You have extra extra fat cells, and you have different insulin levels” which can make it feel like you’re eating less than you are.

“And once these effects have taken place, the fat deposition or the insulin changes in your body, then it’s a lot harder to reverse,” Yen tells The Salt.

Take fat cells for instance. Once the body creates a fat cell, it lasts a lifetime.

“You can slim down that fat cell, but that fat cell will always be sitting there waiting to be larger if you give it extra calories,” she says.

So Yen’s advise to parents of young children: If you see signs of a weight problem, it’s better to take action sooner rather than later.

The findings of the new study are based on dietary reports collected from 19,125 children, from toddlers to teens, as part of the National Health and Nutrition Examination Survey (NHANES). The way the survey works is that participants report everything they’ve eaten in a 24 hour period, and researchers separately measure height and weight to calculate BMI (body mass index).

Now, because researchers are not able to verify diets that are self-reported, the study’s findings have some major caveats. Yen and her Stanford colleagues have seen major errors using similar dietician recall methods. And they point out that overweight people tend to under report what they’re eating more than healthy weight people. More research is needed.

Copyright 2012 National Public Radio. To see more, visit http://www.npr.org/.