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Résumé (anglais)

Background: Efforts are needed to identify individuals at risk of becoming obese to facilitate the development and implementation of targeted prevention strategies. The objective of this dissertation was to identify the developmental trajectories of body mass index (BMI) among children as they age into adulthood and examine how the neighbourhood environment influences childhood obesity rates and BMI development. Methods: Data from Canada’s National Longitudinal Survey of Children and Youth was used for this dissertation. Group based trajectory modeling was used to examine eight waves (14 years) of data to identify distinct trajectories of BMI. Neighbourhood types were defined by grouping neighbourhoods with similar attributes using latent class analysis. A mediation analysis was then conducted to assess the mediating role of physical activity and sedentary behaviour on the cross-sectional relationship between neighbourhood type and obesity. The relationship between neighbourhood type and obesity was examined longitudinally using both variable- and person-centred approaches. Results: This study identified four distinct BMI trajectories among children: low, decreasing, medium, and high. Born large for gestational age, living in a rural area, and maternal smoking were associated with the high trajectory. Children were found to live within one of five neighbourhood types. Compared with children living in an affluent urban type neighbourhood, higher rates of obesity were observed in the remaining four neighbourhood types. Physical activity and sedentary behaviour were found to partially mediate the relationship between neighbourhood type and obesity; however, not among children living in predominantly rural neighbourhoods. Children living in predominantly rural neighbourhoods were found to have a significantly higher BMI trajectory and were more likely to be on a BMI trajectory leading to obesity by adulthood. Conclusions: This dissertation identified children at risk of becoming obese by adulthood and neighbourhood types that are most conducive of children developing obesity. The results suggest that prevention efforts should be targeted to children living in rural areas and that these efforts should differ from those applied in urban settings. Physical activity explains a small proportion of obesity risk suggesting that other factors (e.g., diet) may play an important role in obesity risk associated with neighbourhood factors.