Positive expressive writing has greater benefits for positive affect in individuals reporting better dietary quality and higher dietary fibre intake

Background: Positive expressive writing is associated with enhanced psychological wellbeing. Several individual differences are known to moderate the enhancement effects of positive expressive writing, but no studies to date have investigated the optimal dietary conditions under which expressive writing effects occur. Here, we sought to investigate whether diet quality and dietary fibre intake moderates the effects of positive writing on mood. Methods: Participants completed self-reported measures of dietary quality, dietary fibre intake, and positive and negative affect. They were then randomly allocated to complete either a positive expressive writing or neutral writing activity for 10 minutes. Positive and negative affect were measured again immediately after each activity. Results: Participants who reported better diet quality and greater dietary fibre intake exhibited a significantly greater increase in positive affect following positive expressive writing, relative to neutral writing. No significant effects were observed for negative affect. Conclusion: For the first time, we report that effects of positive expressive writing on positive mood are enhanced under optimal dietary conditions. Further replication studies are needed to determine whether dietary factors can influence the conditions under which positive expressive writing benefits occur. We speculate that dietary influences on the gut-brain axis are a potential mechanism.