Predicting adolescent eating and activity intentions and behaviors using the theory of planned behavior: Focus on perceived social norms and personal agency

Guided by the Theory of Planned Behavior (TPB), this study examined predictors of healthy eating and physical activity in a sample of 279 adolescents. This theory predicts behavior from attitudes, social norms, perceived behavioral control, and behavioral intentions. The purpose of the study was to improve our knowledge about behavioral predictors among adolescents by making developmentally-guided modifications to the TPB. Extensions of the theory focused on the social norms and perceived behavioral control (PBC) constructs. The influence of social norms was tested (a) separately for different social influences, and (b) through indirect pathways. A multidimensional assessment of psychological control, based on action-theory, was tested in models. In a test of the standard TPB model, all paths were significant, except, consistent with previous research, the social norms-intention path. Social norms did predict intentions indirectly, through their effect on attitudes. Examining the unique impact of specific social influences (i.e., parents versus peers separately) provided additional information over testing social influences as an aggregate group (e.g., parents and peers grouped together). The action-theory measure of control provided more detail by examining global versus self-related and intra-versus extra-agentic beliefs. Certain types of control beliefs, particularly intra-agentic agency beliefs, were associated with stronger intentions to eat healthily or be active. Others, such as intra-agentic causality beliefs, appeared to have a negative influence on intentions and subsequent behavior. Results differed slightly across behaviors and gender. Results highlight important theoretical issues (e.g., the importance of examining the impact of specific social influences and the utility of a more detailed assessment of personal agency) and provide potential targets for future research on programs aimed at promoting healthy eating and activity among youth.