Does stage of change predict outcome in a primary-care intervention to encourage an increase in fruit and vegetable consumption?

Abstract

Our aim was to investigate the response of participants in different Stage of Change (SOC) groups to an intervention to increase fruit and vegetable consumption. Participants recruited from a primary-care health centre were entered into a trial investigating an intervention to increase fruit and vegetable consumption. A total of 729 men and women were randomized into intervention and control groups. Participants attended two appointments 6 months apart and completed postal questionnaires before each appointment. The questionnaire included SOC questions which were used to classify participants into 'pre-contemplation', 'contemplation' and 'action' groups at baseline and at follow-up. All intervention participants received a standard intervention to increase consumption of fruit and vegetables to at least five portions per day. After 6 months at the end of the trial control participants received the same intervention. The main outcome measures were the changes in plasma concentrations of antioxidant vitamins. Changes in self-reported fruit and vegetable intake were a secondary outcome measure. At baseline, 38% (113/297) of the intervention participants were described as being in the 'pre-contemplation' stage, 35% in 'contemplation' and 27% in 'action' groups. For control participants, 36% (112/310) were in 'pre-contemplation', 34% in 'contemplation' and 30% in 'action' groups. In the intervention groups, 50% (57/113) of 'pre-contemplators' moved to the 'action' stage and 37% (42/113) moved to 'contemplation'. There was little movement in the control 'SOC' groups between baseline and follow-up, other than a small drift to 'contemplation'. Overall, the intervention group reported a greater increase in fruit and vegetable consumption than the controls (mean difference in change of 1.4 daily portions; 95% confidence interval 1.2, 1.6; after adjustment for baseline intake and gender) and significantly greater changes were reported in all three intervention 'SOC' groups compared to the corresponding 'control' groups (P < 0.001 in each case). These results suggest that peoples' SOC may have little bearing on their success in increasing fruit and vegetable consumption.