MD assessment instruments

We used two short MD questionnaires in this study. The MDSS questionnaire [26] was being validated and the MEDAS questionnaire [23] was selected as the gold standard, due to its extensive previous use in the literature.

The Mediterranean Diet Serving Score (MDSS) is an MD index that was originally validated against the Mediterranean Dietary Score (MDS), proposed by Trichopoulou et al. [40]. In the validation study on 1,155 women aged 12–83 years from Spain, both MDSS and MDS indexes were based on the data obtained from the semi-quantitative food frequency questionnaire (FFQ) [26]. It was found that MDSS index was “an updated, easy, valid, and accurate instrument to assess MD adherence based on the consumption of foods and food groups per meal, day, and week” [26], while being in accordance with the latest update of the Mediterranean Diet Pyramid [16, 26]. MDSS index incorporates 14 typical MD food groups, and individuals whose intake is within the recommended range receive either 3, 2, or 1 points for each of the specific food groups consumption per meal, daily or weekly, while those individuals who don’t reach the particular goal get 0 points (Table 1).

Therefore, the MDSS index can range between 0 and 24 points for adults and between 0 and 23 for adolescents, since alcoholic beverages intake is not considered appropriate in this age group [26]. Out of the maximum 24 points, 12 points (50%) can be obtained for recommended intake of fruits, vegetables, cereals, and olive oil (3 points each, for consumption during every main meal). Additional 4 points can be obtained for daily intake of dairy products and nuts (2 points each), and 8 points for weekly intake of legumes, potatoes, eggs, fish, white meat, red meat and sweets (Table 1). According to the original study, people with a score of ≥13.5 on the MDSS scale can be considered as adherent to the principles of the MD, which we rounded up to 14 points (Table 1) [26]. The same MDSS scoring system was used in our previous study in the general population of Dalmatia, but the data were obtained through the FFQ [41]. We did not use the FFQ in this study due to the more extensive burden of this approach to the subjects. Instead, we have used only 14 questions including food groups that comprise the original MDSS index (S1 Table), with the exception that we didn’t include beer in the fermented beverages, as originally proposed [26]. Instead, we only included wine, which is in accordance with the modern MD pyramid [16]. Additionally, the question on juices and sugar-sweetened beverages was introduced as a separate item, but it was scored within sweets, as proposed [26]. The full questionnaire is presented in both Croatian and English in S1 Table.

Mediterranean Diet Adherence Screener (MEDAS) was chosen as a gold standard needed to assess the validity of the MDSS index. Since MEDAS was not previously validated for application in Croatian language, we used the same steps for questionnaire preparation as for the MDSS questionnaire, and we also performed MEDAS test-retest reliability assessment.

The original version of MEDAS was designed and validated in Spain [23, 25]. It was translated into several languages and validated for use in Germany [28], Iran [29], UK [30], Turkey [31], Korea [32] and Portugal [33]. The original version of the MEDAS questionnaire contains 14 items (S1 Table), with 12 questions about the frequency of food consumption, and two items are about the eating habits characteristic for the Spanish area [23]. Each item is scored with either a 0 or 1, with the overall score ranging between 0 and 14 (Table 1). There are two ways to categorize the overall MEDAS score. Subjects can be divided into 3 subgroups, where the score of ≤5 points indicates low adherence, 6–9 indicates moderate adherence and ≥10 points indicates high level of adherence to the principles of the MD (Table 1) [23, 25]. Additionally, a cut-off score of ≥8 points has been used to denote adherence to the principles of the MD, while MEDAS score of ≤7 points represents MD non-adherence [23]. Croatian version of the MEDAS questionnaire is presented in S1 Table.

There are some differences between MEDAS and MDSS questionnaires. For example, some food groups are included in MDSS and not in MEDAS, such as cereals, dairy products, eggs, and potatoes. MDSS separates fruit juices from fresh fruit consumption and it does not include processed meat, unlike MEDAS. On the other hand, MEDAS incorporates sofrito sauce, butter or margarine or cream and sweetened beverage intake as separate groups, whereas all types of juices are regarded as sweets according to the MDSS questionnaire scoring [26]. MEDAS distinguishes between cooked and raw vegetables and includes two questions on olive oil, which is not the case in MDSS index. Furthermore, there is a difference in proposed frequency of consumption for nuts, legumes, fish and red meat. MEDAS questionnaire aims to incorporate higher intake of traditional Mediterranean staples, such as vegetables, fruits, olive oil and fish, but it also takes into account some of the non-traditional, Western type of foods, such as already mentioned margarine or cream, processed meat and sweetened beverages, demanding their lower intake. On the other hand, MDSS questionnaire asks only about consumption of the traditional MD foods, entirely in accordance to the recommendations of the modern MD pyramid [16, 26]. MDSS is also giving more weight to the foods at the base of the MD pyramid and more points are awarded for higher intake of vegetables, fruit, cereals and olive oil, unlike in the MEDAS index. All of these differences between MDSS and MEDAS are presented in Table 1.