Abstract
Obesity is a significant risk factor for several chronic diseases and represents the leading health risk in Australia. The built environment of residential areas provides opportunities for people to engage in health behaviours, including physical activity (PA), which consequently impacts body weight. Substantial research reports associations between built environment features and adult body weight outcomes. While PA is often assumed to mediate the built environment-body weight relationship, evidence supporting this association remains less clear. This research aimed to clarify whether and to what extent PA contributes to the built environment-obesity relationship, thereby advancing our understanding of the underlying causal mechanisms to help design targeted interventions.The first objective of this thesis was to systematically review the current literature on PA's mediating role in the built environment-body weight association. This review (Paper 1) appraised how PA has been empirically assessed as a mediator across various definitions and measures of the built environment, PA, and obesity, an analysis not previously conducted. Findings indicated that PA mediates the relationship between the built environment and unhealthy body weight, but longitudinal evidence was lacking, and there was only limited examination of domain-specific PA such as walking for transport (WfT). These gaps informed the design of two subsequent studies addressing the second thesis objective: to empirically assess PA's mediating role in the relationship between the built environment and body mass index (BMI).
For these studies, data from a multilevel longitudinal study (HABITAT: How Areas in Brisbane Influence HealTh and AcTivity) were utilised. This dataset consisted of 11,035 middle-aged to older adults (40-65 years at baseline) living in 200 neighbourhoods of Brisbane, Australia. In empirical study 1 (Paper 2), mixed-effect regression and generalised structural equation modelling approaches were used to examine the contribution of WfT to the longitudinal association between neighbourhood walkability and BMI. This study revealed that living in a walkable neighbourhood was significantly associated with greater WfT and lower BMI, with minutes spent walking explaining 7.8% of the walkability-BMI relationship. Empirical study 2 (Paper 3) examined the mediating role of WfT in the longitudinal association between residential density and BMI and further assessed whether this mediating association varied by different quintiles of neighbourhood disadvantage. The study found that density is associated with lower BMI through its positive influence on transport-related walking, which mediated approximately 6.44% of the density-BMI relationship overall. This mediating effect was strongest in moderately disadvantaged neighbourhoods (14.62% mediation), with considerable variations between the most advantaged and most disadvantaged neighbourhoods.
This research provides evidence of the contribution of PA as a mediator in the association between built environment and body weight. The findings suggest that creating walkable, higher-density neighbourhoods can positively influence PA and body weight outcomes, potentially reducing chronic disease risk at the population level. However, this research also indicates the need for context-specific interventions that consider neighbourhood socioeconomic status. Built environment modifications should be implemented alongside complementary health promotion strategies to create environments that support healthy behaviours to maintain healthy body weight across diverse communities.
| Date of Award | 2025 |
|---|---|
| Original language | English |
| Supervisor | Suzanne CARROLL (Supervisor), Gavin TURRELL (Supervisor) & Victor OGUOMA (Supervisor) |