Factors associated with successful dietary changes in an energy-reduced Mediterranean diet intervention: a longitudinal analysis in the PREDIMED-Plus trial

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 energy-reduced MedDiet questionnaire after 6 and 12 months of follow-up. Successful compliance was defined 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-efficacy in modifying diet (OR(6-month): 1.51, 95% CI 1.25–1.83; OR(12-month): 1.66, 95% CI 1.37–2.01), higher baseline fiber intake (OR(6-month): 1.62, 95% CI 1.07–2.46; OR(12-month): 1.62, 95% CI 1.07–2.45), having > 3 chronic conditions (OR(6-month): 0.65, 95% CI 0.53–0.79; OR(12-month): 0.76, 95% CI 0.62–0.93), and suffering depression (OR(6-month): 0.80, 95% CI 0.64–0.99; OR(12-month): 0.71, 95% CI 0.57–0.88). CONCLUSION: Our results suggested that recruitment of individuals with high perceived self-efficacy to dietary change, and those who initially follow diets relatively richer in fiber may lead to greater changes in nutritional recommendations. Participants with multiple chronic conditions, specifically depression, should receive specific tailored interventions. TRIAL REGISTRATION: ISRCTN registry 89898870, 24th July 2014 retrospectively registered http://www.isrctn.com/ISRCTN89898870. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s00394-021-02697-8.