Assessing and comparing the short-term effects of TPB only and TPB plus implementation intentions interventions on snacking behavior in Iranian adolescent girls: a cluster randomized trial.

PURPOSE

The evidence for the effectiveness of theory of planned behavior (TPB)-based interventions is mixed. There is also mixed evidence on the effectiveness of adding implementation intentions to TPB-based interventions. In this study we assessed and compared the short-term effects of TPB-only intervention and TPB plus implementation intentions intervention on snacking behavior and intention to consume unhealthy snacks in Iranian adolescent girls.

DESIGN

Three-arm cluster randomized controlled trial.

SETTING

Ten middle schools in Tehran (Iran).

SUBJECTS

A total of 29 classes included 739 female adolescents (age range: 12-15 years). Intervention. Two brief interventions including TPB-only intervention and TPB plus implementation intentions intervention.

MEASURES

Food frequency questionnaire and intentions at baseline, 10 days, and 3 months measuring snacking behavior and cognitions about unhealthy snack consumption, respectively.

ANALYSIS

Hierarchical linear modeling to assess the interventions' effects.

RESULTS

Both interventions successfully decreased intention to consume and consumption of unhealthy snacks at postintervention. Calculation of the effect sizes revealed that the TPB plus implementation intentions intervention was more effective than the TPB-only intervention. The effects remained significant at 3-month follow-up in the TPB plus implementation intentions intervention group only, although the effect size decreased.

CONCLUSION

Overall, the study suggests that adding implementation intentions on top of TPB-based persuasive messages improves effectiveness and sustainability of desirable changes.