Despite fruit and vegetable consumption’s substantial health benefits for physical health and the reduction of disease risk (World Health Organisation, 2002), many young adults fail to consume recommended quantities of fruit and vegetables (Australian Bureau of Statistics, 1997). This design and evaluation of an intervention intended to increase fruit and vegetable consumption in Australian young adults is reported in the present thesis. The intervention was guided by the theory of planned behaviour (Ajzen, 1991; Fishbein & Ajzen, 2010) and focused on increasing fruit and vegetable consumption through change in attitude, subjective norms, and perceived behavioural control. The intervention was designed on the basis of extensive preliminary work which guided the selection of a theoretical framework and identified salient beliefs that should be targeted in intervention materials. Intervention content was based on findings from preliminary quantitative and qualitative research presented. Analyses showed that the intervention was highly acceptable to participants but did not lead to significant changes in fruit and vegetable consumption relative to the control condition. Despite the fact that the theory of planned behaviour provided a good model for the prediction of fruit and vegetable consumption across multiple studies, results indicate that the theory could not be meaningfully be applied to the modelling of change in fruit and vegetable consumption in this population. This finding adds to the growing body of research suggesting that models that can be reliably applied to the prediction of behaviour are not necessarily applicable to behaviour change (Hardeman, Kinmonth, Michie, & Sutton, 2011).
Researchers who wish to use theories such as the theory of planned behaviour in health research should consider the implications of this research for both intervention design and behaviour change theory more broadly. Specifically, researchers should consider the evidence that the TPB may not be an effective means to develop interventions designed to increase fruit and vegetable intake.