Purpose Long-term nutrition trials may fail to respond to their original hypotheses if participants do not comply with the intended dietary intervention. We aimed to identify baseline factors associated with successful dietary changes towards an energy-reduced Mediterranean diet (MedDiet) in the PREDIMED-Plus randomized trial. Methods Longitudinal analysis of 2985 participants (Spanish overweight/obese older adults with metabolic syndrome) randomized to the active intervention arm of the PREDIMED-Plus trial. Dietary changes were assessed with a 17-item energyreduced MedDiet questionnaire after 6 and 12 months of follow-up. Successful compliance was defned as dietary changes from baseline of≥5 points for participants with baseline scores<13 points or any increase if baseline score was≥13 points. We conducted crude and adjusted multivariable logistic regression models to identify baseline factors related to compliance. Results Consistent factors independently associated with successful dietary change at both 6 and 12 months were high baseline perceived self-efcacy in modifying diet (OR6-month: 1.51, 95% CI 1.25–1.83; OR12-month: 1.66, 95% CI 1.37–2.01), higher baseline fber intake (OR6-month: 1.62, 95% CI 1.07–2.46; OR12-month: 1.62, 95% CI 1.07–2.45), having>3 chronic conditions (OR6-month: 0.65, 95% CI 0.53–0.79; OR12-month: 0.76, 95% CI 0.62–0.93), and sufering depression (OR6-month: 0.80, 95% CI 0.64–0.99; OR12-month: 0.71, 95% CI 0.57–0.88). Conclusion Our results suggested that recruitment of individuals with high perceived self-efcacy to dietary change, and those who initially follow diets relatively richer in fber may lead to greater changes in nutritional recommendations. Participants with multiple chronic conditions, specifcally depression, should receive specifc tailored interventions.