A new study by University of North Carolina School of Medicine pediatrics researchers finds a surprising difference in the eating habits of overweight children between ages 9 and 17 years compared to those younger than 9.

Younger children who are overweight or obese consume more calories per day than their healthy weight peers. But among older overweight children the pattern is reversed: They actually consume fewer calories per day than their healthy weight peers.

How to explain such a seemingly counterintuitive finding?

"Children who are overweight tend to remain overweight," said Asheley Cockrell Skinner, PhD, assistant professor of pediatrics at UNC and lead author of the study published online Sept. 10, 2012 by the journal Pediatrics.

"So, for many children, obesity may begin by eating more in early childhood. Then as they get older, they continue to be obese without eating any more than their healthy weight peers," Skinner said. "One reason this makes sense is because we know overweight children are less active than healthy weight kids. Additionally, this is in line with other research that obesity is not a simple matter of overweight people eating more -- the body is complex in how it reacts to amount of food eaten and amount of activity."

These results also suggest that different strategies may be needed to help children in both age groups reach a healthy weight. "It makes sense for early childhood interventions to focus specifically on caloric intake, while for those in later childhood or adolescence the focus should instead be on increasing physical activity, since overweight children tend to be less active," Skinner said. "Even though reducing calories would likely result in weight loss for children, it's not a matter of wanting them to eat more like healthy weight kids -- they would actually have to eat much less than their peers, which can be a very difficult prospect for children and, especially, adolescents."

These findings "have significant implications for interventions aimed at preventing and treating childhood obesity," Skinner said.

In the study, Skinner and co-authors Eliana Perrin, MD, MPH, and Michael Steiner, MD, examined dietary reports from 19,125 children ages 1-17 years old that were collected from 2001 to 2008 as part of the National Health and Nutrition Examination Survey (NHANES). They categorized the weight status based on weight-for-length percentile in children less than 2 years old, or body mass index (BMI) percentile for children between 2 and 17, and performed statistical analyses to examine the interactions of age and weight category on calorie intake.

All three study authors are faculty members in the UNC Department of Pediatrics.