Do behavioural health intentions engender health behaviour change? A study on the moderating role of self-affirmation on actual fruit intake versus vegetable intake


Suzanne Pietersma, Department of Social and Organizational Psychology, University of Groningen, Grote Kruisstraat 2/1, 9712 TS Groningen, the Netherlands (e-mail:


Objectives. The purpose of this persuasion research was to show that self-affirmation (SA) increases intentions in the advocated direction and that these intentions predict actual health behaviour change. That is, these intentions not only serve the function of short-term relief of the threat caused by the persuasive message. We proposed that the effect of SA depends on the level of value-involvement.

Design. Participants were randomly assigned to one of two conditions (no SA vs. SA) of a between-subjects design. After the SA manipulation, all participants read a threatening health text about the consequences of insufficient fruit and vegetable intake. At pre-test, value-involvement was determined.

Methods. Participants included were undergraduate students. The SA manipulation consisted of a writing exercise. After reading the health message, participants reported their intention to eat sufficient fruit and vegetables (N= 537). After 1 week (N= 293) and 4 weeks (N= 261), participants completed self-reports of fruit and vegetable intake.

Results. No main effect was found for SA on any outcome measure. We did find that involvement moderated the effect of SA on cooked vegetables consumption. This effect was not present for raw vegetables/salad consumption or for fruit consumption. The moderated effect on cooked vegetable consumption was most evident after 1 week and the effect was mediated by the immediate intentions of participants.

Conclusions. SA can lead to genuine intentions that predict actual behaviour, but the effect of SA depends on the type of behaviour and people's value-involvement.