Background: Unhealthy eating has been found to be associated with the prevalence of depressive symptoms. However, prospective evidence of the combined effects of unhealthy eating and depressive symptoms has not been reported. This study aimed to elucidate the prospective relationship between habitual unhealthy eating habits and depressive symptoms.

Methods: A 2-year prospective cohort study of 376 Japanese adults aged 24–83 years without depressive symptoms at baseline was conducted. Information about participants' eating behaviors was obtained via a self-administered questionnaire, in which skipping breakfast, eating dinner shortly before bedtime, and snacking after dinner were recorded. Depressive symptoms were assessed using the Japanese version of the Zung Self-rating Depression Scale.

Results: The 2-year incidence of depressive symptoms was found to be 23.7% (89/376). Covariate-adjusted multivariate Poisson regression analyses showed that habitual snacking after dinner was significantly associated with the incidence of depressive symptoms (relative risk [RR] 1.77; 95% confidence interval [CI], 1.00–3.14, p = 0.049), whereas no relationship was found between skipping breakfast or eating dinner shortly before bedtime and depressive symptoms. On the other hand, there was an interaction effect of snacking after dinner and dinner before bedtime on depressive symptoms ( p for the interaction = 0.044). Participants with more than two unhealthy eating behaviors had a higher incidence of depressive symptoms compared to those with fewer than two unhealthy eating behaviors (RR 1.71; 95% CI, 1.06–2.77, p = 0.028).

Conclusions: This prospective study is the first to reveal the combined relationship between unhealthy eating and the incidence of depressive symptoms.