Distinct Patterns of Urban-Rural and Sex Disparities in Children's BMI Trajectories From 2013 to 2018

Background: To identify distinct trajectories of body mass index (BMI) in a large sample of Chinese children by urban-rural and sex disparities. Methods: Data for this study were obtained from the National Surveys on Chinese Students' Constitution and Health among 16,060 children aged 6-11 years. Weight and height data were used to calculate BMI. Group-based trajectory modeling (GBTM) was used to identify distinct BMI trajectories. Results: Seven distinct trajectories were identified, "sustained healthy weight " (46.01%), "sustained obesity " (17.26%), "sustained underweight " (4.50%), "obesity to overweight " (6.45%), "obesity to healthy weight " (11.75%), "healthy weight to overweight " (8.67%), and "healthy weight to obesity " (5.36%). The proportions of "sustained obesity, " "healthy weight to obesity, " and "healthy weight to overweight " trajectories were much higher among boys compared with girls (P < 0.001). Meanwhile, children living in rural areas were more represented in the "healthy weight to obesity " trajectory (P < 0.001). Conclusion: In this study, the proportions of BMI development trajectories among 6-11-year-old children varied by sex and urban-rural areas, which may require tailored interventions specifically toward these at-risk trajectories.