Self-regulation in adopting the Mediterranean diet: an experimental study

Despite its advantages, the Mediterranean diet (MD) is still under-diffused, making it necessary to understand the psychological variables underlying its adoption. Using an integrated model of Theory of Planned Behavior (TPB) and Self-Determination Theory (SDT), the present study evaluated the efficacy of experimentally manipulating motivation (autonomous vs controlled) to change intention and MD adherence. The study consisted of two phases, with a time lag of two weeks. At T1, 726 Italian adults were randomly allocated to one of three conditions: autonomous motivation, controlled motivation and control group. In the experimental conditions, participants answered a verbal stimulus aimed at increasing their autonomous or controlled motivation to adhere to MD. TPB and SDT variables were measured at T1, except for the behavior, which was measured at T2, along with a second measurement of motivation. Participants in the autonomous motivation condition reported higher intention, attitude and autonomous motivation (both at T1 and T2) than those in the control group. Nevertheless, no change in behavior was found. Our study showed the effectiveness of targeting motivation to promote intention to adhere to MD, also suggesting the importance of further exploring the intention-behavior gap.