2.5. Sample Size
The sample size of this two-arm parallel randomized controlled trial was established to observe a statistically significant difference of at least one point in the PREDIMED score (standard deviation (S.D.) = 2, effect size = 0.5) between the experimental and control groups at the end of the intervention time (4 months after first visit), while adjusting for the baseline value as a covariate by analysis of covariance (ANCOVA), assuming a minimum correlation coefficient of 0.4 between the baseline and end of the study value in the control group. According to a 1:1 randomization plan, an enrollment of 70 subjects per group, assuming a maximum of 20% loss of subjects for the end of the intervention time, would have provided more than 80% power for statistically significant ANCOVA for testing the between-groups difference at the threshold of 0.05.