The role of autonomous motivation in predicting the adherence to the Mediterranean diet

The study explores the role of autonomous motivation in the Theory of Planned Behavior (TPB; Ajzen, 1991) applied to the adherence to the Mediterranean diet. The hypothesized model integrates the TPB (extended with descriptive norm) with the inclusion of autonomous motivation, a construct from self-determination theory (SDT; Deci & Ryan, 1985). The autonomous motivation reflects personally endorsed, self-referenced reasons for acting. The main aim was to test whether autonomous motivation moderates the relationship between intention and behavior. The study was conducted in two phases, with a time lag of two weeks. In the first phase, the online structured questionnaire included measures of intention and its antecedents and items to detect autonomous motivation. In the second, the behavior of adherence to the Mediterranean diet in the previous two weeks was surveyed. A convenience sample of 225 Italian adults (66.7% were university students) participated in the study. Results of the regression analyses proved that the TPB-extended model explained 66.2% of the intention variance, and 15.3% of behavior variance. Affective attitude, descriptive norm, perceived behavioral control and autonomous motivation were significantly related to intention. Behavior was directly predicted by intention. Furthermore, autonomous motivation moderated the effect of intention on behavior, which was significant only when autonomous motivation was high. In conclusion, the results support the importance of integrating SDT and TPB in predicting the intention to adhere to this healthy and sustainable diet and the usefulness of this integration in order to better understand the intention-behavior gap.