Tailoring a fruit and vegetable intervention on novel motivational constructs: Results of a randomized study

BACKGROUND: Tailored health communications to date have been based on a rather narrow set of theoretical constructs. PURPOSE: This study was designed to test whether tailoring a print-based fruit and vegetable (F & V) intervention on relatively novel constructs from self-determination theory (SDT) and motivational interviewing (MI) increases intervention impact, perceived relevance, and program satisfaction. The study also aimed to explore possible user characteristics that may moderate intervention response. METHODS: African American adults were recruited from two integrated health care delivery systems, one based in the Detroit Metro area and the other in the Atlanta Metro area, and then randomized to receive three tailored newsletters over 3 months. One set of newsletters was tailored only on demographic and social cognitive variables (control condition), whereas the other (experimental condition) was tailored on SDT and MI principles and strategies. The primary focus of the newsletters and the primary outcome for the study was fruit and vegetable intake assessed with two brief self-report measures. Preference for autonomy support was assessed at baseline with a single item: "In general, when it comes to my health I would rather an expert just tell me what I should do". Most between-group differences were examined using change scores. RESULTS: A total of 512 (31%) eligible participants, of 1,650 invited, were enrolled, of which 423 provided complete 3-month follow-up data. Considering the entire sample, there were no significant between-group differences in daily F & V intake at 3 month follow-up. Both groups showed similar increases of around one serving per day of F & V on the short form and half a serving per day on the long form. There were, however, significant interactions of intervention group with preference for autonomy-supportive communication as well as with age. Specifically, individuals in the experimental intervention who, at baseline, preferred an autonomy-supportive style of communication increased their F & V intake by 1.07 servings compared to 0.43 servings among controls. Among younger controls, there was a larger change in F & V intake, 0.59 servings, than their experimental group counterparts, 0.29 servings. Conversely, older experimental group participants showed a larger change in F & V, 1.09 servings, than older controls, 0.48. CONCLUSION: Our study confirms the importance of assessing individual differences as potential moderators of tailored health interventions. For those who prefer an autonomy-supportive style of communication, tailoring on values and other motivational constructs can enhance message impact and perceived relevance.