Can combined goal prioritization and implementation intentions promote adherence to the Mediterranean Diet? A randomized controlled trial.

Adherence to the Mediterranean Diet (MD) requires the simultaneous regulation of multiple distinct dietary behaviors, often creating a significant intention-behavior gap. This study evaluated the efficacy of a combined goal prioritization and implementation intentions intervention in promoting adherence to specific MD components, testing whether individuals can prioritize selected targets while successfully maintaining adherence to non-prioritized health behaviors. In a longitudinal randomized controlled trial, 410 adults (Mage = 46.1) were randomized to an experimental condition, in which they selected two MD behaviors to prioritize and formed prioritization plans, or to an active control condition. Primary analyses were conducted on the full randomized sample with missing values handled using multiple imputation. The intervention produced a small increase in self-reported goal priority, which was not maintained at follow-up, and had no significant effect on adherence across the MD components relative to control. In exploratory within-person analyses, adherence to the behaviors participants had chosen to prioritize showed a small positive change over time while non-prioritized behaviors remained statistically equivalent to no change, although the difference between the two trajectories was significant only at the alpha level of 0.10. Because the prioritized behaviors were self-selected, this pattern is observational and is treated as a potential mechanism warranting a controlled test. These findings suggest that inducing prioritization is feasible but not sufficient, on its own, to shift adherence in a complex dietary pattern.