Longitudinal associations between dietary intake and common mental disorders among adolescents in Australia

Background There is a need for more longitudinal research exploring temporal associations between diet quality and common mental disorders (CMDs) during adolescence. This study examined prospective associations between indicators of adolescents' diet quality (fruit, vegetable, sugar‐sweetened beverage [SSB] intakes) and risk of depression and anxiety onset over 3 years. We hypothesised that higher fruit and vegetable intake, and lower SSB intake, would be associated with lower risk of CMDs. Methods 6537 Australian adolescents (mean age 12.65 years at baseline) completed surveys at baseline, 1‐, 2‐ and 3‐year follow‐ups. We fitted Generalised Estimating Equations Poisson regression models to assess longitudinal associations between daily servings of fruit, vegetables and SSBs, and risk of depression and anxiety onset (binary cut‐points on validated scales) over 3 years. Models were re‐run for males and females. Analyses excluded participants who met thresholds for depression or anxiety at baseline to increase confidence that diet predicted CMD onset. Results Higher fruit intake was associated with lower risk of depression (adjusted RR: 0.87, 95% CI: 0.82–0.93) and anxiety (adjusted RR: 0.93, 95% CI: 0.87–0.99) over 3 years, with limited evidence of sex differences. Higher SSB intake (log‐transformed) was associated with higher CMD risk for both sexes, but more strongly for males (depression: adjusted RR: 3.25, 95% CI: 2.02–5.23; anxiety: adjusted RR: 5.50, 95% CI: 3.39–8.90) than females (depression: adjusted RR: 3.10, 95% CI: 2.06–4.68; anxiety: adjusted RR: 2.04, 95% CI: 1.23–3.37). Results inform the Global burden of disease Lifestyle And mental Disorders project (DERR2‐ https://doi.org/10.2196/65576 ). Conclusions Longitudinal research exposing temporal associations between diet and CMDs may inform prevention/intervention efforts targeting modifiable risk factors for CMDs.