Temporal changes in Mediterranean-style diet adherence and ultra-processed food exposure in relation to psychological distress at follow-up: A 12-year analysis of the Melbourne Collaborative Cohort Study

Background Consuming a Mediterranean-style diet is associated with lower depression risk. Concurrently, the ultra-processed food (UPF) dietary pattern is associated with increased depression risk. As dietary patterns shift over time, it is important to understand how changes in these dietary patterns relate to psychological distress as an indicator of depression. Methods We used a subset of data from the Melbourne Collaborative Cohort Study (n = 21,718). Dietary intake was assessed at baseline and follow-up using food frequency questionnaires, from which Mediterranean diet scores and UPF exposure were derived. Psychological distress at follow-up was measured using the Kessler Psychological Distress Scale (K10). We assessed change in diet from baseline to follow-up using generalised estimating equations to account for repeated measures, and associations of change in diet with psychological distress using Poisson regression. Analyses were conducted in the overall sample and by birthplace (Australian/New Zealand/Northern European; Southern European). Results Participants increased both their adherence to the Mediterranean-style diet (β = 0.28, 95%CI = 0.25–0.31) and exposure to UPFs (β = 55.20 g/day, 95%CI = 51.71–58.69). Stratification by birthplace showed similar patterns, except for Southern European participants where no clear change in UPF exposure was observed (β = −2.38 g/day, 95%CI = -12.35–7.59). One-point increases in Mediterranean diet score between baseline and follow-up were associated with a 5% lower risk of psychological distress (RR = 0.95, 95%CI = 0.93–0.98), while increasing UPF by 90 g/day was associated with a 5% higher risk (RR = 1.05, 95%CI = 1.03–1.07). Conclusions Adherence to Mediterranean-style diet and UPF exposure increased over time across the overall sample, although patterns varied by birthplace, and these changes were associated with opposing risks of psychological distress.