The prevalence of childhood obesity has reached epidemic levels. Reducing it will require a substantial effort from health care professionals as well as from families, schools, government agencies, and community organizations. These efforts must be guided by current information about this epidemic.
DEFINITIONS OF OVERWEIGHT AND AT RISK FOR OVERWEIGHT
Overweight is a complex, chronic health problem that may be established at a young age and is difficult to reverse. Clinical definitions of childhood overweight are based on the ratio of weight to height using age- and sex-specific references from national databases.1 The body mass index (BMI), which is calculated by dividing weight (in kilograms) by height (in meters) squared, is a widely accepted proxy measure of adiposity. A child's BMI percentile can be used to identify the child as overweight or at risk for overweight. A child or adolescent is considered at risk for overweight when the BMI is between the 85th and 94th percentiles. A child or adolescent is defined as being overweight when the BMI is at or above the 95th percentile.2
Although BMI is now the preferred measure of overweight, other measures may be used as alternatives if and when there is a reason to do so. For example, overweight was long defined as the relationship between the child's weight and height in terms of the ideal percentage of body weight for height. Some clinicians still find this useful for parent counseling.3
PREVALENCE AND PERSISTENCE OF CHILDHOOD OVERWEIGHT
The prevalence of overweight children has risen markedly in the past 3 decades (Figure 1, see page 20). Recent data indicate 10% of children ages 2 to 5 and 15% of children ages 6 to 19 are overweight.4 Prevalence of childhood overweight varies by racial/ethnic group, with highest rates for Mexican-American children, followed by non-Hispanic blacks (Figure 2, see page 2 1).4 It is likely that physiologic and cultural influences account for the finding that the development of adiposity varies by age and among racial/ethnic groups.5 Impoverished children are more often overweight than their economically advantaged peers.6
Overweight children are more likely to become overweight adults than are children who have healthy weights. The risk of sustained overweight rises from approximately 20% at age 4 to 80% by adolescence and is already marked by age 7.7 When childhood obesity persists into adulthood, it is associated with higher rates of morbidity and mortality than adult-onset obesity.8
Prevalence of Excess Weight Among Children and Adolescents from 1963 to 2000
CONSEQUENCES OF CHILDHOOD OVERWEIGHT
Health and social consequences of overweight occur during childhood. Overweight in childhood is associated with early menstruation, hyperlipidemia, and hepatic steatosis.9 An increasing number of overweight children have impaired glucose tolerance or type 2 diabetes.10 Overweight children also have a higher risk for disorders of lipid metabolism and cardiovascular disease." Overweight children are more likely to experience sleep disturbances that may necessitate treatments for obstructive sleep apnea, and may also experience social ostracism. 12 Emotional and social difficulties related to overweight can severely affect children throughout adolescence and into adulthood.12
RISK FACTORS AND CORRELATES
There are strong genetic influences on the development of overweight. Children with an overweight parent are more likely to be overweight than those whose parents are not overweight.13 Lifestyle plays a part, as a genetic shift cannot plausibly explain recently rising rates of childhood obesity.14 The prenatal environment also influences the development of child overweight. Children born to mothers with diabetes have an increased risk of overweight, as do children with higher birth weights.15
Research on the phenomenon of resumed adipose cell proliferation after the toddler pause, referred to as adiposity rebound, has demonstrated that earlier adipose rebound is a risk factor for development of overweight before age 25. 16 The timing and explanatory power of the adiposity rebound appears to cut across classes and cultures. Children with overweight parents are more likely to experience an early adiposity rebound.17 Another key time in the maturation process is puberty, when adipose tissues proliferate again.18 The patterns of weight gain for women are apparent by age 11, with those who become overweight after age 25 significantly differing from never-overweight women.16
Childhood lifestyle factors influence the development and sustainability of childhood overweight, with breastfeeding demonstrating a protective effect on the development of child overweight.19 However, it is unclear whether this is a direct effect or due to linkages between health behaviors within a family. A number of studies have demonstrated that dietary choices play a role in the development of overweight. For example, there is evidence that high levels of sweetened beverage consumption in children are associated with an increased risk of overweight.20 However, other studies have found similar dietary habits for overweight and nonoverweight older children.21
Studies have described positive associations between the occurrence of childhood overweight and excessive television viewing,22 which contributes to decreased energy expenditure.23 For children ages 6 to 17, this relationship persists when controlling for race, socioeconomic status, and other family variables.24 Televisions in children's bedrooms have been associated with a higher risk for overweight among lowincome preschool children.25
Overweight children have lower levels of physical activity. Studies have reported an inverse relationship between physical activity and measures of triceps skinfold and BMI in young children.26 Trost et al.27 compared physical activity patterns and psychosocial and environmental determinants in a diverse cohort of obese and non-obese middle-school children. The study found obese children had lower levels of physical activity, reported lower levels of physical activity selfefficacy, were less involved in community organizations that promote physical activity, and were reported to have less physically active fathers.
Parents influence their children's dietary intakes through their own attitudes and beliefs. Parental pressuring of the child to eat and degree of concern that the child would become overweight was shown to account for 15% of the variance in a child's dietary intake.28 It is possible that parents who overly restrict their child's diet may limit the child's ability to self-regulate food intake through interpretation of internal satiety cues.29 Parental beliefs on the importance of establishing healthy dietary practices to prevent disease have been shown to influence dietary habits among school-aged children.30
It has been amply demonstrated that modeling can have a strong influence on child behavior,31 and children may, in part, adopt a healthy lifestyle due to the modeling that parents provide.32 Parental dietary and exercise behaviors strongly influence the development of these behaviors in young children.33 Similarly, the family has a powerful influence in shaping and maintaining the eating habits and food preferences of its members.34 Family meals at home are healthier than meals eaten away from home.35
PREVENTION AND MANAGEMENT
The prevention of overweight through improving dietary and physicalactivity habits of children is an important focus of public health efforts. An effective and empowering prevention message should be consistently applied across the age spectrum, involve all family members who will model desired health behaviors, and be culturally acceptable.
Previously suggested strategies to prevent childhood overweight generally focus behavior changes on identified risk factors for overweight.36 Universal prevention programs, an acceptable strategy for all children, have generally been applied in the school setting.37 In a small study, adolescents in primary-care settings completed a computerized assessment of physical activity and dietary behaviors that was then used to create a tailored action plan. Participants reported improved dietary and activity behaviors at 4 months of follow-up.38
Current Prevalence of Excess Weight Among Children by Racial/Ethnicity Group
Selective prevention programs that focus on prevention of weight gain in high-risk children (eg, children of obese parents) and targeted interventions, which are performed for overweight children on a case-by-case basis, have not been evaluated in the primary care setting. No studies have implemented routine application of pediatric-practice guidelines and evaluated their effectiveness on the prevention of child overweight or the promotion of family dietary and physical-activity behaviors. Clinical prevention is discussed in detail in the paper by Dennison and Boyer on page 25.
Clinical overweight management programs can address the risk factors discussed in this article, guided by the conceptual framework that Golan and Weizman39 have developed. They proposed that parental display of healthy behaviors through modeling and provision of environmental changes that foster opportunities for child health are the key elements for child adoption of desired health habits. The success of parental-behavior changes is tied to their concerns about their child's longterm health outcomes and their knowledge of means to improve the health environment for the family. Management of the overweight young child is discussed in the paper by Ariza, Greenberg, and Unger, on page 33.
The pediatric office has an important role in national efforts to reverse rising trends in the prevalence of childhood overweight. Overweight may be established at a young age and is difficult to reverse. Lifestyle choices associated with overweight are common and their development may begin in very young children. Therefore, there is a necessity to apply a preventive strategy that addresses all children to promote healthy lifestyle choices from birth onward and to develop an intervention strategy that works by changing family habits so that healthy lifestyle habits are reinforced. It is crucial to develop, evaluate, and apply new systems and practical approaches to aid in this effort in the pediatric practice setting.
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