Growing up strong: Pathways to healthy Body Mass Index in the Longitudinal Study of Indigenous Children

Aboriginal and Torres Strait Islander (hereafter ‘Indigenous’) cultures are among the longest-surviving in the world. There is a significant gap between the health of Indigenous and non-Indigenous Australians, stemming from Australia's history of colonisation. High Body Mass Index (BMI) is a leading contributor to this health gap; Indigenous Australians aged 15 years and over are 20% more likely to be overweight and 60% more likely to be obese than non-Indigenous Australians. Limited cross-sectional data indicate an elevated prevalence of overweight and obesity among Indigenous, versus non-Indigenous, Australian children. Despite the high burden, there is no evidence specific to Indigenous Australians on trajectories of BMI across childhood, or on the relation of key factors to the development of overweight and obesity. This thesis provides the first evidence on BMI trajectories and associated factors in Indigenous Australian children, using data from up to 1,759 children aged 0-10 years participating in the national Longitudinal Study of Indigenous Children. The majority of children were in the normal BMI range across waves of the study; the prevalence of overweight/obesity increased from 12.1% to 41.9% of children aged around 3 and 9 years, respectively. There was a rapid onset of overweight/obesity in the sample: 31.9% of children who had a normal BMI at age 3-6 years had become overweight or obese three years later. Children born large-for-gestational age (versus appropriate-for-gestational age) and exposed to smoke in utero (versus not exposed) had significantly higher BMI at age 3-8 years. Female (versus male) and Torres Strait Islander (versus Aboriginal) children increased in BMI at a faster rate. We observed cross-sectional and longitudinal evidence of lower childhood BMI in disadvantaged areas. Findings were consistent with a protective effect of healthier diets (low consumption of sugar-sweetened beverages and high-fat foods) on children’s BMI trajectories. This thesis provides the first detailed analysis of the relationship between diet – a key risk factor for high BMI – and sociocultural and environmental factors in the Indigenous Australian context. Financial security, high parental education, quality housing, and community cohesion were associated with improved child nutrition (reduced odds of consuming soft drink; reduced likelihood of facing barriers to accessing fruit and vegetables). This work confirms the pervasiveness of issues surrounding food availability, quality, and affordability in remote/outer regional settings, and identifies that disadvantaged Indigenous families in urban/inner regional settings also face these barriers to a healthy diet. Efforts are critically required to reduce the prevalence of overweight and obesity among Indigenous Australian children in the first 3 years of life, and to slow the rapid onset of overweight/obesity from age 3-9 years. Improving maternal risk profiles during pregnancy and improving nutrition in the first decade of life are likely to promote healthy BMI trajectories. However, improving nutrition will require both addressing the underlying determinants of nutrition and improving the food environment in urban, regional, and remote settings. Throughout the course of this project, I have identified, developed, and applied methods for conducting meaningful large-scale Indigenous health research, and have demonstrated their suitability for broader adoption