Diet, Physical Activity and Depression: Does Gastrointestinal Health Help Explain the Relationship Between Lifestyle Factors and Depression?

Lifestyle factors such as diet and physical activity are involved in the development and maintenance of depression, but the mechanism by which these factors influence mental health remains unclear. The aim of this study was to investigate whether gastrointestinal health helps explain some of the relationship between these lifestyle factors and depression. The study used a cross-sectional design to compare dietary intake, physical activity and gastrointestinal health in three groups, healthy (n = 235), lifetime depression (n = 161) and current depression (n = 86). Dietary intake was measured by the Fruit And Vegetable VAriety index, N-3 PUFA Food Frequency Questionnaire and Prebiotic and Probiotic Food Frequency Questionnaire. Analysis of variance, Pearson correlations and Hayes PROCESS macro mediation analysis were used to compare the groups and examine the relationships. Physical activity and gastrointestinal health differed significantly between the groups with no differences in overall fruit and vegetable, omega-3 and probiotic food intake. Bootstrapped correlations showed that higher fruit and vegetable and omega-3 intake were associated with lower gastrointestinal symptom and depression scores, but effects were weak. Furthermore, higher occurrence of gastrointestinal symptoms was moderately associated with higher depression scores. Results from a series of exploratory mediation analyses suggested that gastrointestinal symptoms mediated the relationship between lifestyle factors and depression status. These data indicate that the effects of lifestyle factors on depression might partly work through the gastrointestinal system. The findings of this study help further understand the mechanisms between dietary intake and physical activity, and depression and can inform future longitudinal and experimental studies.