Data set contains processed data from the Slovenian national dietary survey SI.Menu 2017/18, conducted among a representative sample of Slovenian adults aged 18–74 years (n = 850). The dataset includes socio-demographic and socio-economic variables (sex, age, education, place of residence, cohesion region, and self-reported material status), as well as dietary data based on a food frequency questionnaire (FFQ). The dataset includes calculated MDI scores and categorisation of participants into adherent and non-adherent groups.