Synergistic effects of social support and self-efficacy on dietary motivation predicting fruit and vegetable intake

•Self-efficacy, intention, and social support can explain fruit and vegetable intake.•A mechanism was found among these predictors that starts with dietary self-efficacy.•When receiving social support, the motivational effect of self-efficacy is stronger.•Self-confident, supported individuals more likely translated intention into action. Background: Self-efficacy and social support are considered relevant predictors of fruit and vegetable intake. This study examines whether the effect of self-efficacy on fruit and vegetable intake is mediated by intention and whether this motivational process is moderated by received dietary social support. Methods: A longitudinal study with two measurement points in time, four weeks apart, on fruit and vegetable intake was carried out with 473 students aged 19 years on average (52% women). In a conditional process analysis, dietary intention was specified as a mediator between self-efficacy and fruit and vegetable intake, whereas received dietary support was specified as a moderator of the self-efficacy–intention association, controlling for baseline fruit and vegetable intake. Results: Self-efficacy was positively associated with fruit and vegetable intake four weeks later, and intention mediated this process. Moreover, an interaction between received dietary support and self-efficacy on intention emerged. Conclusions: The effect of self-efficacy on fruit and vegetable intake was fully mediated by intention. Moreover, received support exhibited a moderating role within the motivational process: high dietary support appeared to accentuate the positive relationship between self-efficacy and dietary intention.