Greater fruit and vegetable (F&V) intake has been linked to more positive mood. Here, the purpose of this paper is to examine if this relationship is mediated by expectancies about their benefit to health/mental health.
Participants completed a new questionnaire to assess expectancies related to F&V intake. This was administered alongside a validated food-frequency measure of F&V intake, an assessment of positive and negative mood state and other measures.
Participants held strongly positive expectations about the physical and mental health benefits of consuming F&V. The authors observed a significant relationship between self-reported F&V intake and positive mood (d = 0.52). Importantly, this effect was largely (but not completely) independent of expectancies. The authors also observed that expectancies about F&V intake were independently predictive of positive mood (d = 0.47).
This is the first study to explore expectancy effects in the mental health benefits of F&V intake. These data suggest that positive expectancies about F&V intake, and F&V intake itself, are both predictive of positive mood. The former finding is probably a placebo effect, whereby people believe they are consuming sufficient F&V (even if they are not) and so experience mood-related benefits due to their positive expectations. The latter finding is consistent with F&V exerting a biologically beneficial effect on the brain.
