From motivation to mediterranean diet intention and behavior: a combined self-determination theory and theory of planned behavior approach

Objective: The Mediterranean diet (MD) is recognized as one of the healthiest and most sustainable dietary patterns worldwide. This study combines the Theory of Planned Behavior (TPB) and Self-Determination Theory (SDT) alongside past MD adherence behavior to predict MD adherence among young and adult Italians. Methods and measures: Using a two-wave prospective design, 706 participants (Women = 60.5%, mean age = 31.82) completed measures of past behavior, SDT and TPB variables at baseline (T1) and reported their adherence behavior to MD two weeks later (T2). Results: Results revealed that both intention and past adherence to MD predicted actual adherence. In turn, affective attitude, descriptive norm, perceived behavioral control (PBC), and autonomous motivation were positively associated with intention. Past adherence further predicted autonomous motivation, affective attitude, and PBC, and indirectly influenced MD adherence at T2 through its effect on these factors and intention. Finally, invariance tests showed no differences between women and men and between student and non-student samples. Conclusion: Overall, our findings support the integration of TPB and SDT, emphasizing the need for interventions that address both conscious decision-making and established dietary habits, acknowledging the multifaceted nature of dietary behavior change.