Background: Substantial studies have revealed the potential mechanisms underlying the link between dietary behaviour and depression symptoms. This study investigated the relationship between depression symptoms and dietary behaviour, physical activity, and sleep quality in a nationwide sample of Chinese residents.

Methods: A total of 18 819 Chinese Residents completed the dietary behaviour, patient health questionnaire, international physical activity questionnaire, and Pittsburgh sleep quality index. We used the Hayes' serial mediation model to investigate the correlation between the variables.

Results: Among the participants, 85.5% were aged between 18 and 59, 41.2% were male, and 73.8% were urban residents. There is a negative correlation between dietary behaviour and physical activity (r = -0.038, P < 0.001), while there is a positive correlation with depression symptoms (r = 0.238, P < 0.001) and sleep quality (r = 0.115, P < 0.001). Additionally, depression shows a positive correlation with physical activity (r = 0.024, P < 0.001) and sleep quality (r = 0.298, P < 0.001), while there is a negative correlation between physical activity and sleep quality (r = -0.035, P < 0.001). Dietary behaviour was found to be connected with depression symptoms via three mediation pathways: (1) physical activity (B = -0.003, 95% confidence interval (CI) = -0.016, -0.007), (2) sleep quality (B = 0.034, 95% CI = 0.126, 0.164), and (3) physical activity and sleep quality (B = 0.001, 95% CI = 0.001, 0.003).

Conclusions: These findings highlight the significance of psychological and physical factors in exploring the mechanisms through which dietary behaviour is related to depression symptoms. Overall, this study showed the important role of lifestyle factors in depression symptoms, suggesting that appropriate dietary behaviours, appropriate physical activity, and good sleep quality are necessary for the avoidance or improvement of depression symptoms.