Comparing implementation intention interventions in relation to young adults’ intake of fruit and vegetables

Abstract

This study tests whether the effectiveness of implementation intention-based interventions to increase fruit and vegetable intake in a young adult population can be enhanced using additional pre-intervention instructions and alternative formats; namely, an ‘if-then’ implementation intention versus a more general, ‘global’ plan that does not explicitly link a situational cue with a goal-directed response. Participants (N = 557) completed pre-test measures of planning, motivation and behaviour with respect to increasing their fruit and vegetable intake before being randomised to a 3 (intervention format: control vs. ‘if-then’ vs. ‘global’ implementation intentions) × 2 (pre-intervention instruction vs. no pre-intervention instruction) between-participants design. Results revealed a significant intervention format by time interaction, such that intake significantly increased by 0.50 portions in the if-then format condition compared with 0.31 in the global format and 0.01 in the control condition. These results suggest that ‘if-then’ manipulations are superior in promoting behaviour change in an applied setting. The use of pre-intervention instructions had no additional effect on behaviour, providing evidence for the efficacy of implementation intentions even when experimenter demand is reduced. Evidence is also presented to suggest that reported increases in intake are not related to demand characteristics.

Keywords:

• implementation intentions
• fruit and vegetables
• dietary change
• planning

Notes

Notes

1. Because the measure is designed for epidemiological studies, it is not sufficiently sensitive to detect small changes in dietary intake (e.g. from 1–2 times a week to 1–3 times a month).

2. The univariate comparison between responders and non-responders that is close to significance (F(1,556) = 3.55, p = 0.06) was for pre-test planning measures, M = 3.87, SD = 2.06 and M = 4.22, SD = 2.25 for responders and non-responders, respectively.

3. Participants who were ‘unaware’ of the study aims wrote ideas such as ‘surveying eating habits’. Interestingly however, the majority of ‘unaware’ participants thought that the main purpose of the study was to ‘assess how closely people attend to the wording of questions’ and ‘how repeated questioning affects answers’.