The Mediterranean diet (MD) has garnered significant attention for its association with various health benefits, including a reduced risk of cardiovascular diseases and other illnesses. This dietary pattern, rooted in the traditional eating habits of countries bordering the Mediterranean Sea, emphasizes the consumption of vegetables, fruits, legumes, whole grains, fish, and olive oil, while limiting the intake of red meat, processed foods, and saturated fats. However, accurately measuring an individual's adherence to the MD can be challenging due to the diverse range of assessment methods available.
The Challenge of Measuring Adherence to the Mediterranean Diet
Nutritional epidemiology traditionally focuses on the relationships between individual nutrients or foods and their impact on health. However, this approach can be limiting, as it often overlooks the complex interactions between multiple dietary components. In recent decades, the study of dietary patterns, such as the MD, has gained prominence as it allows for the evaluation of multiple dietary factors as a single exposure.
Despite the growing recognition of the MD's health benefits, accurately measuring adherence to this dietary pattern remains a significant challenge. A key limitation in studies examining the effects of the MD on health is the variety of methods used to assess adherence. This diversity in assessment approaches raises concerns about the comparability and interpretation of study results. The concordance between different methodologies has been questioned, and their evaluation is recommended to establish a standardized measuring tool.
Exploring Different Mediterranean Diet Indexes
To address the challenge of measuring MD adherence, researchers have developed various indexes, each with its own set of criteria and scoring systems. These indexes aim to quantify an individual's adherence to the key components of the MD, providing a standardized measure for research and clinical purposes. Several indexes exist for measuring adherence to the Mediterranean diet pattern.
Mediterranean Diet Score (MDS)
The Mediterranean Diet Score (MDS), developed by Trichopoulou et al., is a widely used index that considers nine food groups: vegetables, legumes, fruit, fish, cereals, meat, dairy products, the ratio of monounsaturated to saturated fats, and alcohol consumption. The MDS assigns scores based on the consumption frequency of these food groups, with higher scores indicating greater adherence to the MD.
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Alternative Mediterranean Diet (aMED)
The Alternative Mediterranean Diet (aMED) index takes into account vegetables, legumes, fruit, nuts, fish, whole grains, red meat, the ratio of monounsaturated to saturated fats, and alcohol consumption. Similar to the MDS, the aMED assigns scores based on consumption frequency, with higher scores reflecting greater adherence to the MD.
Relative Mediterranean Diet (rMED)
The Relative Mediterranean Diet (rMED) index considers vegetables, legumes, fruit, cereals, fish, olive oil, meat, dairy products, and alcohol. This index, like the MDS and aMED, assigns scores based on consumption frequency, with higher scores indicating greater adherence to the MD.
Dietary Score (DS)
The Dietary Score (DS) includes vegetables, legumes, fruits, fish, whole grains, potatoes, olive oil, poultry, dairy products with fat, red meat, and alcohol. Unlike the previous indexes, the DS uses predefined criteria, rations, grams, or energy density to assign scores, rather than relying on the distribution of the study sample.
Literature-Based Adherence Score (LBAS)
The Literature-Based Adherence Score (LBAS) considers vegetables, legumes, fruits, fish, whole grains, olive oil, dairy products, red meat and processed meat, and alcohol. Similar to the DS, the LBAS uses predefined criteria based on general dietary recommendations to assign scores, rather than relying on the distribution of the study sample.
Mediterranean-Style Dietary Pattern Score (MSDPS)
The Mediterranean-Style Dietary Pattern Score (MSDPS) is based on the recommended intakes of 13 food groups in the Mediterranean diet pyramid: whole-grain cereals, fruits, vegetables, dairy, wine, fish, poultry, olives-legumes-nuts, potatoes, eggs, sweets, meats, and olive oil. Each food group is scored from 0 to 10 depending on the degree of correspondence with recommendations. Exceeding the recommendations results in a lower score proportional to the degree of overconsumption. The sum of the component scores is standardized to a 0-100 scale and weighted by the proportion of energy consumed from Mediterranean diet foods.
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Concordance Among Different Indexes
A study evaluated the agreement among five indexes that measure adherence to a Mediterranean dietary pattern: Mediterranean diet score (MDS), alternative Mediterranean diet (aMED), relative Mediterranean diet (rMED), dietary score (DS) and literature-based adherence score (LBAS). The study population included healthy adults selected in the Multi-Case Control Spain (MCC-Spain) study recruited in 12 provinces. A total of 3640 controls were matched to cases by age and sex.
The relative frequency of subjects with a high level of adherence to a MD varied from 22% (aMED index) to 37.2% (DS index). Similarly, a high variability was observed for the prevalence of a low level of MD: from 24% (rMED) to 38.4% (aMED). The correlation among MDS, aMED and rMED indexes was moderate, except for MDS and aMED with a high coefficient of correlation 0.75 (95% CI 0.74-0.77). The Cohen’s Kappa coefficient among indexes showed a moderate-fair concordance, except for MDS and aMED with a 0.56 (95% CI 0.55-0.59) and 0.67 (95% CI 0.66-0.68) using linear and quadratic weighting, respectively.
The existing MD adherence indexes measured the same, although they were based on different constructing algorithms and varied in the food groups included, leading to a different classification of subjects. Therefore, concordance between these indexes was moderate or low.
Factors Influencing Concordance
Several factors can contribute to the variability in results obtained from different MD adherence indexes. These include:
- Different constructing algorithms: Each index employs a unique algorithm for calculating the final score, which can lead to variations in the classification of individuals.
- Variations in food groups included: The specific food groups included in each index can differ, potentially leading to discrepancies in the assessment of adherence.
- Scoring criteria: The criteria used to assign scores for each food group can vary across indexes, contributing to differences in the final scores.
- Dependence on study population: Some indexes, such as the MDS, aMED, and rMED, use criteria dependent on the study sample, while others, like the DS and LBAS, use independent criteria based on general dietary recommendations.
Implications of Low Concordance
The moderate or low concordance observed among different MD adherence indexes raises concerns about the potential for misclassification bias. Depending on the index used, individuals may be classified differently in terms of their adherence to the MD, which can impact the results of research studies and clinical assessments.
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Developing a Mediterranean-Style Dietary Pattern Score (MSDPS)
To address the limitations of existing MD scores, researchers developed a Mediterranean-Style Dietary Pattern Score (MSDPS) to assess the conformity of an individual's diet to a traditional Mediterranean-style diet. The MSDPS is based on the recommended intakes of 13 food groups in the Mediterranean diet pyramid. Each food group is scored from 0 to 10 depending on the degree of correspondence with recommendations. Exceeding the recommendations results in a lower score proportional to the degree of overconsumption.
The MSDPS has four unique features relative to other previously published scores of Mediterranean-style dietary patterns:
- It is constructed based on the Mediterranean diet pyramid.
- It has 13 components that correspond to the 13 food groups of the Mediterranean diet pyramid.
- Each group is scored from 0 to 10 depending on the degree of correspondence with recommendation.
- It takes into account the negative implications of overconsumption, defined as exceeding the recommended intake of foods in the Mediterranean diet pyramid.
Applying the MSDPS to Dietary Data
The MSDPS was applied to dietary data from the Framingham Heart Study (FHS) Offspring Cohort. The mean MSDPS was 24.8 (range 3.1-60.7). Participants with a higher MSDPS were more likely to be women, older, multivitamin users, to have lower BMI and waist circumferences, and less likely to be current smokers. The MSDPS demonstrated content validity through expected positive associations with intakes of dietary fiber, (n-3) fatty acids, antioxidant vitamins, calcium, magnesium, and potassium, and inverse associations with those of added sugar, glycemic index, saturated fat, and trans-fat, and the (n-6):(n-3) fatty acid ratio.