Validation of the German version of the Mediterranean Diet Adherence Screener (MEDAS) questionnaire

The MD has been tested for its health benefits in different at-risk populations with favourable results. For instance, randomized controlled intervention studies revealed that MD is effective in the primary prevention of cardiovascular diseases [ 1, 2], in lowering hypertension and atherogenic lipoproteins [ 3, 4] and in improving diabetes [ 5]. More recently, studies in the older population showed an association between MD and improved cognitive function [ 6]. Epidemiological studies from the European Prospective Investigation into Cancer and Nutrition (EPIC) cohort suggested further that MD might protect against cancer, especially gastric cancer [ 7], colorectal cancer [ 8] and bladder cancer [ 9].

Such trials raised the need for a useful tool to assess MD adherence in study populations. The PREDIMED consortium established a 14-point MEDAS questionnaire, which was validated by administering the established FFQ [ 10] and MEDAS to 7146 participants from the PREDIMED study. The authors found that the average MEDAS score estimate was 105% of the FFQ PREDIMED score estimate, and thus is a valid instrument for rapid estimation of adherence to the MD [ 11]. Moreover, the PREDIMED investigators could show that MEDAS is able to capture a strong monotonic inverse association between adherence to MD and obesity indices in a population of adults with a high cardiovascular risk [ 12].

In Germany, a multicentre trial, the ‘Lifestyle intervention in BRCA 1/2-mutation carriers’ (LIBRE) was launched to investigate the effect of a defined lifestyle intervention on breast cancer incidence in women at high genetic risk for this type of cancer [ 13]. Up to 60% of women with BRCA mutations develop breast or ovarian cancer [ 14], but not all of them, suggesting that environmental co-factors play a role. Indeed, some studies suggested that physical activity and dietetic intervention help prevent cancer, including breast cancer [ 15, 16]. To test the hypothesis of whether these controllable environmental factors further modulate cancer risk, the LIBRE trial conducts an intervention with clearly defined sport and nutrition components. The nutritional component of the intervention was based on the MD. The German translation of MEDAS was used as an instrument to assess adherence. The purpose of the present study was to validate the German version of MEDAS.

MEDAS was developed for the Spanish PREDIMED study to expediently determine adherence to the MD and allow an immediate feedback to the patient. This short screener is a validated tool for the rapid assessment of adherence to the MD [ 11], which is why it was decided to use a German-translation of this questionnaire in the LIBRE study. However, the original MEDAS was not in German. To validate the German translation of this questionnaire, we used the validated German full-length FFQ as reference.

In general agreement between FFQ and MEDAS questionnaires was of a fair or better level (0.4 and larger values for agreement coefficients) for about half of the MEDAS questions [ 22]. These differences are likely due to the way FFQ is structured and to the fact that it is differently analyzed. FFQ measures the food frequency of a selected list of German foods with standardized portion sizes for the previous 12 months. These answers are then used to calculate intake for food groups while MEDAS directly asks for the habits and consumption frequency of specific amounts of specific Mediterranean foods during the previous week. In short, the FFQ measures specific details whereas the MEDAS is measuring for components of an overall dietary pattern. For the conversion of food intake data from FFQ into MEDAS food groups only aggregated FFQ data can be used in most cases. For instance, question 3 on vegetables and question 4 on fruits each comprised several questions from FFQ. A further example is that FFQ provides, 3no information on how many times boiled vegetables, pasta, rice, or other dishes with a sauce of tomato, garlic, onion, or leeks sautéed in olive oil are consumed. It asks only about the consumption of tomato sauce, but no further details (e.g. way of cooking or ingredients). Only question 9 (pulses) which has a high concordance is based on a direct answer of FFQ. Additionally, in this study FFQ was completed again within after an interval of just 3 months, which means that the answers for the two time points for FFQ in our analysis overlap for a period of time.

The Bland-Altman analysis showed that the MEDAS score yields higher values for the sum of all items than FFQ with respect to MD. This confirms the results of Schröder et al., who report that the average MEDAS Mediterranean diet score estimate was 105% of the FFQ PREDIMED score estimate [ 11]. The larger difference between the two score sets after 3 months can be a result of the MD-based intervention in the IG. The MEDAS questionnaire was specifically developed to detect the adherence of an individual’s diet to the principles of the MD. Therefore, MEDAS is more sensitive for MD items than FFQ, resulting in higher scores in individuals abiding by the MD. The FFQ questions, however, assesses the general food intake and does not focus particularly on the consumption of Mediterranean food. Two points can be considered relevant for detecting an adequate implementation of MD in life.

To confirm if the MEDAS’ tendency towards the MD is consistent, we analyzed the association between certain MD food items and selected dietary intake biomarkers in the blood thought to be associated with these food items. The traditional MD is characterized by a high intake of olive oil, fruit, nuts, vegetables, and cereals; a moderate intake of fish and poultry; and a low intake of dairy products, red meat, processed meats, and sweets; while wine is consumed moderately and only together with meals [ 1, 23]. In the literature, it is described that a high consumption of fruits and vegetables is associated with higher β-carotene blood levels [ 26]. Kitamura et al. have previously positively correlated frequency of vegetables and fruit intake with β-carotene, among other things [ 26]. In our study, subjects who consumed at least two portions of vegetables per day according to the MEDAS questionnaire had higher β-carotene blood levels than those who consumed fewer than two portions at both time points. Those who consumed at least three portions of fruit per day according to the MEDAS questionnaire also had higher β-carotene levels in their blood than those who consumed fewer than three portions. This data supports that the MEDAS results reflect the reported intake of particular nutrients charachterisic of a MD pattern.

The MD is rich in poly- and mono-unsaturated fatty acids due to the high consumption of olive oil, fish and nuts [ 27]. The amount of saturated fatty acids in the MD is lower than in the Western-style diet, because red meat and processed meat products play a minor part in the Mediterranean nutrition. The Western-style diet is characterized by its highly processed and refined foods and high contents of sugars, salt and fat and protein from red meat [ 28]. Olive oil is characterized by a high content of mono-unsaturated fatty acids. Oleic acid (C18:1, n-9) is the main component of olive oil [ 27]. Therefore, we hypothesized that a high consumption of olive oil, fish and nuts and low red meat intake are associated with changes in the fatty acid profile measured in erythrocyte membrane. Barcelo et al. described elevated values of omega-3-fatty acids and low values of omega-6-fatty acids following high olive oil consumption, while the omega-9-fatty acid amount remained unchanged [ 29]. Our data demonstrated that, more than four tablespoons of olive oil per day were associated with a tendency to higher serum levels of all unsaturated fatty acids (omega-6, −3 and −9) compared with the values measured in subjects who consumed less olive oil. Takkumen et al. described an association between high fish consumption and a change in the omega-6 and −3-fatty acids profile. The amount of omega-6-fatty acids decreased while that of omega-3-fatty acids increased [ 30]. At least three portions of fish and seafood per week were statistically significantly associated with lower omega-6-fatty acids values (24% compared to 26.3%, p = 0.016) and higher omega-3-fatty acids values. While high meat consumption is associated with higher omega-6-fatty acids values [ 30], such tendencies could also be seen in this study.

Barceló et al. [ 29] also reported an association between hsCRP values and olive oil consumption. According to their data, a MD enriched with olive oil (1 litre per week) resulted in a reduction of the plasma hsCRP concentration. Such tendencies could also be seen in this study. Individuals who consume more than four tablespoons of olive oil per day had lower values of hsCRP than individuals who consume less olive oil. The described associations between certain food items and blood values indicate that the MEDAS score indeed reflects a MD. Within this context, MEDAS provides reasonable estimates to adequately rank MD adherence.

Study limitations comprise firstly, a small sample size meaning the statistical tests would only have small power. A further limitation of this study is that our findings may not apply to the general population as the participants belonged to a selected population who may have a particular dietary behaviour due to their knowledge about their genetic disposition for breast cancer.

We will be using the German MEDAS in our main trial that aims to recruit 600 study participants. We decided to use the adherence to MD measured by the MEDAS score as one of 3 co-primary endpoints [ 31].

Despite the study limitations, we conclude that the present version of MEDAS could be a reasonable tool in determining adherence to a MD in German-speaking populations. This short screener is a valid tool for the rapid assessment of adherence to the MD that may also be useful not only for trials but also in clinical practice. The MEDAS score would allow an immediate feedback to study participants or patients regarding their adherence to MD.