A systematic literature review and meta-analysis: The Theory of Planned Behavior's application to understand and predict nutrition-related behaviors in youth

Background: Efforts to reduce unhealthy dietary intake behaviors in youth are urgently needed. Theory-based interventions can be effective in promoting behavior change; one promising model is the Theory of Planned Behavior (TPB). Purpose: The aim of this study was to determine, using a systematic literature review, how the TPB has been applied to investigate dietary behaviors, and to evaluate which constructs are associated with dietary behavioral intentions and behaviors in youth. Methods: Publications were identified by searching electronic databases, contacting experts in the field, and examining an evolving Internet-based TPB-specific bibliography. Studies including participants aged 2-18. years, all TPB constructs discernible and measured with a description of how the variables were assessed and analyzed, were published in English and peer-reviewed journals, and focused on nutrition-related behaviors in youth were identified. Accompanying a descriptive statistical analysis was the calculation of effect sizes where possible, a two-stage meta-analysis, and a quality assessment using tenants from the Consolidated Standards of Reporting Trials (CONSORT) and Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) statements. Results: Thirty-four articles, including three intervention studies, were reviewed. The TPB was most often used to evaluate healthy eating and sugary snack and beverage consumption. Attitude had the strongest relationship with dietary behavioral intention (mean r=0.52), while intention was the most common predictor of behavior performance (mean r=0.38; both p<0.001). All three interventions revealed beneficial outcomes when using the TPB (e.g. Η²=0.51 and ds=0.91, 0.89, and 0.79); extending the Theory with implementation intentions may enhance its effectiveness (e.g. Η²=0.76). Conclusions: Overall, the TPB may be an effective framework to identify and understand child and adolescent nutrition-related behaviors, allowing for the development of tailored initiatives targeting poor dietary practices in youth. However, support from the literature is primarily from observational studies and a greater effort towards examining these relationships within intervention studies is needed.