HARVARD GAZETTE ARCHIVES

A new study by researchers at the Harvard School of Public Health (HSPH) shows that America's overweight teens consumed an average of 700 to 1,000 calories more than required each day over a 10-year period. This "energy gap" - or the imbalance between the number of calories children consumed each day and the number they required to support normal growth, physical activity, and body function - resulted in an average of 58 extra pounds for overweight teens.

The study, the first to look at the energy gap among children and youth, was published in the December 2006 issue of the journal Pediatrics. The study shows that U.S. children and teens overall consumed an average of 110 to 165 more calories than they required each day. Over a 10-year period, this energy gap led to an excess 10 pounds of body weight on average among teens.

"Our research indicates that early prevention may be critical," said Y. Claire Wang, the HSPH researcher who led the study. "The energy gap becomes bigger and harder to close as kids accumulate more excess weight." This suggests that strategies to prevent excess weight gain from occurring during childhood may be more effective than attempting to treat overweight teens.

"We must find ways to help kids eat well and move more," said Tracy Orleans, a distinguished fellow and senior scientist at the Robert Wood Johnson Foundation, which sponsored the study. "That means acting now to create environments that support healthy eating and increased physical activity in schools and communities, and at home."

For the study, researchers examined height and weight data for 5,000 children in the National Health and Nutrition Examination Survey (NHANES) between 1988 and 1994. They projected what the height and weight gains for this group would be 10 years later, based on normal growth patterns, and compared that projection to actual height and weight data from a similar group of teens in the most recent NHANES (1999 to 2002). Children were defined as overweight (sometimes called obese) if their body mass index was greater than or equal to the 95th percentile of the Centers for Disease Control and Prevention (CDC) growth charts.

Childhood obesity rates in the United States have reached epidemic proportions. In the past four decades, obesity rates have more than tripled for children and adolescents ages 6 to 19.

"These data show that no single intervention will be enough to close the energy gap," said Risa Lavizzo-Mourey, president and CEO of the Robert Wood Johnson Foundation. "Reversing childhood obesity will require the best efforts of government, communities, schools, health care providers, families, the food and beverage industries, and others."

The study recommends using a range of strategies to close the energy gap, including:

Consuming less fast food. (Eating at fast food restaurants has been associated with an additional 120 calories per day.)

Decreasing time spent watching TV as a way to increase physical activity and limit exposure to advertising, which has been associated with increased energy intake. (One hour of TV watching replaced by one hour of slow walking is a difference of 55 calories burned. In addition, reducing TV viewing by one hour is associated with 160 fewer calories consumed per day.)