senting twice the expected percentage; and that more than 15 percent of 6-to 19-year-olds met this criterion, representing about three times the expected percentage (Ogden et al., 2002a). No significant increases in obesity prevalence were reported between the 1999-2000 and the 2001-2002 NHANES (Hedley et al., 2004).
A significant, unabated increase in the prevalence of childhood obesity across all age groups is clearly seen in an analysis of serial national surveys from the early 1970s through the year 2000 (Figure 2-1). In the nearly 30 years between the 1971-1974 NHANES and the 1999-2000 NHANES, the prevalence of childhood obesity more than doubled for youth aged 12 to 19 years (from 6.1 percent to 15.5 percent) and more than tripled for children aged 6 to 11 years (4 percent to 15.3 percent). Even for preschool children, aged 2 to 5 years, the prevalence also more than doubled (5 percent to 10.4 percent) between these two national surveys (Ogden et al., 2002a). Data for children younger than 2 years of age, based on weight-for-length data available from NHANES II (6-23 months) onward also suggest an upward trend (Ogden et al., 2002a).
The same trends, stratified by gender, are shown in Figure 2-2 for infants and preschool children and in Figure 2-3 for school-aged children and adolescents. Among children older than 2 years of age, the increased prevalence of obesity over time has occurred to a similar degree in both