Using the theory of planned behaviour to assess if psychosocial determinants of fruit and vegetable intake in a UK adult population change following a dietary intervention

The UK Department of Health recommends the consumption of at least five portions of fruit and vegetables (F&V) a day, but only a third of British men and women are thought to meet this target. This study evaluated whether a dietary intervention (FLAVURS) that seeks to modify F&V intake (FVI) directly in a low-consuming group also changes key underlying psychosocial determinants of behaviour. A sample of low-F&V (⩽3 portions/d) consumers consisting of 154 adults, participated in a randomised controlled study. The intervention group received dietary advice and F&V and the control group was encouraged to consume their habitual diet. Consumer perceptions of FVI were measured pre- and post-intervention (18 weeks apart) using a questionnaire based on the theory of planned behaviour (TPB) in 136 participants. The TPB proposes that behaviour is determined by a combination of people's intentions to engage in that behaviour and their perceptions of control over the behaviour. Intention (INT) in turn, is held to be predicted by attitudes (ATT) towards the behaviour, subjective norm (SN) and perceived behavioural control (PBC). Individual questionnaire items were based on psychosocial determinants of FVI using seven-point, unipolar response scales. All constructs were coded so that higher numbers always reflected a more positive attitude. The questionnaires had separate sections for fruit and vegetable intake and were presented in a balanced order to participants.