Changes in Physical Activity Patterns and Dietary Intake in Chinese Youth and Their Associations with Obesity: A Longitudinal Study in Nanjing City, China

Objectives: Obesity has become a global public health crisis. Ending the childhood obesity epidemic is a global public health priority. Obesity and overweight rates have increased rapidly in China over the past 30 years, especially in urban areas. At present, in China 42% of adults and about 15% of children are overweight or obese. Research on changes in energy balance-related behaviors remain limited in Chinese children. This study aimed to: 1) study the present physical activity (PA) and dietary intake patterns among Chinese school children; 2) examine temporal changes over a one-year follow-up and the related potential sex differences in the children's PA and dietary intakes; and 3) examine the associations between dietary intake and PA with body weight outcomes in these Chinese youth.;Methods: A school-based randomized intervention study was conducted as the Health Legacy Project (HLP) of the 2014 World Summer Youth Olympic Games, Nanjing, China during September 2013 to June 2014. The present study used part of the data (i.e., baseline data from all subjects and the 1-year follow update from those in the control group), and was designed as a 1-year follow study focused on the data collected from the control group. The original HLP project collected data from 10,091 4th and 7th graders from 48 schools (32 primary and 16 junior high schools). The present analysis focused on these 10,091 students' baseline data, and on 4,583 students from the control group to study the 1-year changes. Student t-tests, Wilcoxon-Mann-Whitney tests, Wilcoxon signed rank tests, McNemar's tests, Chi-square tests and ANOVA were conducted. Mixed effects models were fit to assess associations between PA and dietary behaviors and child weight outcomes like BMI-z, overweight and obese. Weight status was classified using the International Obesity Task Force (IOTF) criteria, i.e., age-sex-specific BMI cut points.;Results: There were considerable sex differences in overweight/obesity rates and energy balance-related behaviors in Chinese children in Nanjing. The baseline overweight/obesity prevalence was 30.6% (21.1% in girls and 39.1% in boys). Boys tended to be more likely to consume soft drinks (52.9% vs. 43.6%, p<0.01), eat read meat more than once daily (17.1% vs. 11.9%, p<0.01), and be more physically active (7.4 vs. 5.9 MET-h/d) than girls. During the 1-year follow, the combined prevalence of overweight and obesity increased by 2.4% (1.7% for boys vs. 3.2% for girls). Compared to the 4th graders, the 7th graders had a greater decrease in screen time, fruit and vegetable intake and had a 31.2 min/d (boys vs. girls: 28.7 vs. 34.7 min/d, p<0.05) decrease in sleep time. Analysis of mixed effects models controlling for covariates shows that a one-hour increase in daily sleep time was associated with a 0.03 ( p<0.01) unit decrease in BMI-z and a 35% (p<0.01) decline in the odds of being overweight/obesity; one increase in the frequency of eating red meat daily was associated with a 0.04 (p<0.01) unit increase in BMI-z.;Conclusions: Overweight and obesity are prevalent in urban China as the rates are 21.1% in girls and 39.1% in boys in Nanjing City. Insufficient sleep duration and increased red meat intake are associated with increased BMI-z and an increased risk of overweight/obese among Chinese children. Effective intervention strategies to control childhood obesity may consider these factors as well as the sex- and age differences. Key words: China, children, dietary intake, physical activity, body mass index, overweight, obesity.