The moderating effect of a school based intervention on children's fruit and vegetable intake: An application of the theory of planned behaviour

The Theory of Planned Behaviour (TPB) posits that intentions are the proximal determinants of behaviour. Although it is an effective model for predicting food choice among adults and adolescents, its power to predict children's dietary behaviour is less well established. In this paper, we evaluate the relationship between TPB constructs and fruit and vegetable intake among primary school children, and the moderating effect of a school-based intervention (Project Tomato) on these relationships. Data (intervention and control groups) from a UK national cluster randomised controlled trial of a school based intervention to promote fruit and vegetable intake among 7-8 year olds were analysed. The intervention was informed by the TPB. The primary outcome was change in fruit and vegetable intake, measured at baseline and three months follow-up. Data on the TPB constructs were collected at followup (total n = 537; control n = 282; intervention n = 255). Affective attitudes were significant predictors of intentions to eat fruit and vegetables. However, compared to the control condition, the intervention appeared to reduce intentions to eat fruit, although it increased friends' norms in relation to both fruit and vegetable consumption. The intervention condition also reduced the impact of perceived behavioural control (PBC) on intentions and intentions on intake for fruit. Only baseline intake and affective attitudes, rather than intentions or PBC, predicted fruit or vegetable intake. The research indicates the limited role of intentions and the importance of affective attitudes in understanding children's food choices.