Central obesity and its association with youth physical and mental health: evidence from the Australian National Health Survey

Background: Body fat topography, especially visceral fat accumulation in the abdominal region, is a key risk factor for cardiometabolic and mental health illnesses. This is particularly important for children and young people, as excess abdominal fat gained early in life often leads to obesity in adulthood. This study examined the prevalence and determinants of central obesity, and its association with physical and mental health morbidity among Australian youth using nationally representative data. Methods: This cross-sectional study analysed de-identified data from 3,087 youth (aged 15–24 years) in the 2017–18 Australian National Health Survey. Central obesity was defined as a waist-to-height ratio (WHtR) of ≥ 0.5. Multimorbidity was the presence of ≥ 2 long-term physical (e.g., diabetes, hypertension) or mental (e.g., anxiety, depression) disorders, while physical–mental multimorbidity required at least one of each. A Bayesian multilevel model was employed to identify factors associated with central obesity, and logistic regression was utilised to investigate the relationship between central obesity and morbidity outcomes. Results: The overall prevalence of central obesity among Australian youth (15–24 years) was 33.1% (95% CI: 31.4–34.8). Older youth (aged 18–24 years) had significantly higher odds of central obesity (AOR = 2.31; 95% CI: 1.64–3.27), as did males (AOR = 1.73; 95% CI: 1.39–2.15), those living in the most socioeconomically disadvantaged households (AOR = 2.76; 95% CI: 1.91–4.02), those residing in major cities (AOR = 1.39; 95% CI: 1.01–1.92), and individuals with depression (AOR = 1.61; 95% CI: 1.04–2.49). Additionally, our findings revealed that central obesity was significantly associated with mental disorder (AOR = 1.25; 95% CI: 1.04–1.50), overall multimorbidity (AOR = 1.27; 95% CI: 1.01–1.59), and combined physical–mental multimorbidity (AOR = 1.56; 95% CI: 1.21–2.01). Conclusions: This study highlights central obesity as a key factor associated with both physical and mental health conditions among Australian youth. A life-course perspective that addresses social determinants of health (e.g., access to safe and affordable housing, education, and healthcare) alongside individual lifestyle factors (e.g., balanced diet and regular physical activity) may help mitigate these associations.