Australia is a multicultural society with a strong and continuing migration policy from diverse countries which has led to an increase in its cultural and linguistic diversity [6]. There are public health concerns that children from different priority are disproportionately affected by overweight and obesity [2]. To the best of our knowledge, our study is the first to use longitudinal data from 9417 participants to identify differences in zBMI by cultural, ethnic and socioeconomic groups are associated with higher zBMI during three developmental stages of childhood.

Our results revealed a clear effect of disparities in zBMI for children from different priority populations at three important childhood stages. Children from South and Central Asian, East Asian and African households had a consistently lower zBMI, while those from the Middle East and North Africa, Oceania (excluding Australia and New Zealand) and Americas had consistently higher zBMI than the referent (English) group, at all child developmental ages. Children from European households had similar zBMI to the referent English group. Aboriginal and Torres Strait Islander children had lower zBMI in early childhood, but higher in middle childhood and adolescence. Across all three childhood periods, we consistently found a socioeconomic gradient, with increasingly higher zBMI associated with greater socioeconomic disadvantage.

Our findings indicate that unhealthy weight development during childhood may be culturally patterned and distinctly different across priority populations. Action is needed and additional resources are required to invest in targeted strategies to reduce these disparities in overweight and obesity across all priority populations. We have identified at which period of childhood certain groups are at greater risk, which can help identify optimal timing of interventions for certain age groups, such as early childhood, primary school, or adolescence. For example, prevention in an early childhood setting may not be suitable for Aboriginal and Torres Strait Islander children who have among the lowest zBMI of any cultural group at this age. Similarly, preconception, pregnancy and early infancy programs may be appropriate for prevention initiatives for those that have the highest zBMI between age 2 and 5 years. Middle and high school programs would be suitable for children from Aboriginal and Torres Strait Islander, Americas, Middle East and North African households.

Culturally tailored obesity prevention programs have been found to be effective [28] amongst some cultural and ethnic groups, however only a limited number of programs have been developed in Australia [29]. Currently, there is a lack of programs specifically aimed at addressing Aboriginal childhood overweight and obesity [30], with a need for Aboriginal designed and led initiatives to support self-determination and positive health outcomes [31]. Based on our findings, we suggest a need for more healthy growth programs for Aboriginal and Torres Strait Islander children, and children from the Middle East and North Africa, the Americas and Oceania (excluding Australia and New Zealand) households. Policymakers can use our findings to design strengths-based, community led approaches or culturally adapting existing health programs and public health policies to reduce disparities in children’s weight status in these key groups.

Our results are consistent with both cross-sectional and longitudinal studies in Australia that compared to children from English-speaking backgrounds, children of Middle Eastern and North African, Oceanian and Aboriginal and Torres Strait Islanders had higher prevalence of overweight and obesity whereas children from Asian backgrounds had lower overweight and obesity prevalence [3, 5, 12, 14, 32, 33]. We did not find evidence of higher zBMI in children from a European background, however the existing evidence is mixed, with studies reporting higher [5, 12, 13] and lower [32] odds of overweight and obesity, when compared to children from English-speaking backgrounds.

The strength of this study was the use of a large longitudinal dataset of over 9000 children in Australia with over 100000 person-years of follow-up through childhood. We identified which priority populations are at risk at three important stages of childhood, which provides valuable information for policymakers deciding how to culturally tailor a prevention program and when to intervene in these communities.

Our study has some limitations. Firstly, LSAC did not collect data on self-reported ethnicity or ancestry and our classification of children into nine separate cultural and ethnic groups was conducted using a combination of regions of birth and languages spoken at home using the best available data as recommended [34]. There is potential for children to be misclassified, although 98% of children were classified using two simple decision rules (see Appendix Supplementary Fig. 2). Due to the small sample sizes of some groups, (i.e., Africa and the Americas), we were unable to separate these into further categories to better reflect the diversity of cultural backgrounds of some priority groups in the analysis, nor were we able to stratify our analyses by sex. Finally, our analysis did not use survey weights and although we have a large and diverse sample, our findings may not be representative of the child and adolescent Australian population.