Despite steady progress over most of the past century toward ensuring the health of our country's children, we begin the 21st century with a startling setback—an epidemic of childhood obesity. This epidemic is occurring in boys and girls in all 50 states, in younger children as well as adolescents, across all socioeconomic strata, and among all ethnic groups—though specific subgroups, including African Americans, Hispan-ics, and American Indians, are disproportionately affected. At a time when we have learned that excess weight has significant and troublesome health consequences, we nevertheless see our population, in general, and our children, in particular, gaining weight to a dangerous degree and at an alarming rate.
The increasing prevalence of childhood obesity1 throughout the United States has led policy makers to rank it as a critical public health threat. Over the past three decades, its rate has more than doubled for preschool children aged 2 to 5 years and adolescents aged 12 to 19 years, and it has more than tripled for children aged 6 to 11 years. At present, approximately nine million children over 6 years of age are considered obese. These
■^Reflecting classification based on the readily available measures of height and weight, this report uses the term "obesity" to refer to children and youth who have a body mass index (BMI) equal to or greater than the 95th percentile of the age- and gender-specific BMI charts of the Centers for Disease Control and Prevention (CDC). In most children, such BMI values are known to indicate elevated body fat and to reflect the presence or risk of related diseases.
trends mirror a similar profound increase over the same approximate period in U.S. adults as well as a concurrent rise internationally, in developed and developing countries alike.
Childhood obesity involves immediate and long-term risks to physical health. For children born in the United States in 2000, the lifetime risk of being diagnosed with diabetes at some point in their lives is estimated at 30 percent for boys and 40 percent for girls if obesity rates level off. Young people are also at risk of developing serious psychosocial burdens related to being obese in a society that stigmatizes this condition.
There are also considerable economic costs. The national health care expenditures related to obesity and overweight in adults alone have been estimated to range from approximately $98 billion to $129 billion after adjusting for inflation and converting estimates to 2004 dollars. Understanding the causes of childhood obesity, determining what to do about them, and taking appropriate action require attention to what influences eating behaviors and physical activity levels because obesity prevention involves a focus on energy balance (calories consumed versus calories expended). Although seemingly straightforward, these behaviors result from complex interactions across a number of relevant social, environmental, and policy contexts.
U.S. children live in a society that has changed dramatically in the three decades over which the obesity epidemic has developed. Many of these changes—such as both parents working outside the home, longer work hours by both parents, changes in the school food environment, and more meals eaten outside the home, together with changes in the physical design of communities often affect what children eat, where they eat, how much they eat, and the amount of energy they expend in school and leisure time activities. Other changes, such as the growing diversity of the population, influence cultural views and marketing patterns. Use of computers and video games, along with television viewing, often occupy a large percentage of children's leisure time and potentially influence levels of physical activity for children as well as for adults. Many of the social and cultural characteristics that the U.S. population has accepted as a normal way of life may collectively contribute to the growing levels of childhood obesity. An understanding of these contexts, particularly regarding their potential to be modified and how they may facilitate or impede development of a comprehensive obesity prevention strategy, is essential for reducing childhood obesity.
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