Related Trends in Energy Intake, Energy Expenditure, and Body Mass Index among Chinese School Children and Adolescents from 1991--2004

This study examined related trends in energy intake, physical activity, sedentary activity, and BMI to understand interactive dynamics of these factors associated with or causing overweight (including obesity) among Chinese school children and adolescents. The first part of this study analyzed data from the CHNS collected between 1991 and 2004, which included data about school children (6- to-11-year-olds) and adolescents (12- to-18-year-olds) in seven diverse Provinces. Data about physical activity and sedentary activity only have been collected since 1997. Initial analyses examined trends in: (a) overweight and BMI; (b) energy intake; (c) physical activity; and (d) sedentary activity. Bivariate analysis and sequential multiple regressions were conducted to test relationships among BMI, energy intake, physical activity, and sedentary activity. The second part of this study analyzed 2003 YRBS data from representative high schools in three large Chinese cities and two large U.S. cities to compare the magnitude and variance in prevalence of student overweight, weight perception, and weight control practices in each city. Findings from the first part showed the prevalence of overweight among children and adolescents doubled between 1991 and 2004. Children experienced a notably higher average annual increase in overweight prevalence (0.74% vs. 0.22%) than adolescents, and a higher average relative increase in overweight prevalence (11.7% vs. 6.2%). Changes in energy intake, physical activity, and sedentary activity respectively explained 12% and 28% of the variance in BMI among children and adolescents. Total energy intake remained stable from 1991-2004, but macronutrient composition shifted from carbohydrate to fat. BMI was higher among those who consumed high-fat diets than those who did not. A small significant increase in physical activity was reported. Physical activity significantly was associated with BMI. Sedentary behaviors nearly doubled; half from watching TV/videos and half from studying before and after school. Studying and watching TV/video respectively were associated with increasing BMI. Energy intake, physical activity, and sedentary activity aggregately contributed to increasing BMI. The second part showed in 2003 the proportion of overweight U.S. high school students was nearly twice as high as overweight Chinese students; although more Chinese students perceived themselves to be overweight.

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