Sanchez et al.1 utilized data from the large multi-purpose SUN cohort to examine the association between Mediterranean diet and mental and physical quality of life. The authors found that Mediterranean diet is an important factor associated with health-related quality of life.
Although the results are consistent with the scientific literature on the health benefits associated with the Mediterranean diet,2 it is not clear that the method of assigning diet score is valid for this study. To determine diet score, the investigators categorized intake of each component of the Mediterranean diet using a binary variable (0 for intake below median and 1 for intake above median) and summed the binary variables. This method could have led to a misrepresentation of the magnitude of difference in intake between individuals with different diet scores.
Suppose that most people consumed very near to the median for each of the Mediterranean diet food groups and that differences in intake between individuals were statistically insignificant. In this case, those consuming below (but extremely close to) the median would be assigned a score of 0 and those consuming above (but extremely close to) the median would be assigned a score of 1. This creates an artificial statistical difference between the groups where there was none before.
Although this diet score method, constructed by Trichopoulou et al.,3 has been widely used, the authors should demonstrate its validity for this particular data set by showing that there are significant differences in intake between individuals who received different diet scores. For example, they could report the mean intake for those above and below the median and demonstrate that these values are significantly different from each other. Including this type of information would ultimately help demonstrate that their results are robust.
Sanchez PH, Ruano C, de Irala J, Ruiz-Canela M, Martınez-Gonzalez MA, Sanchez-Villegas A . Adherence to the Medierranean diet and quality of life in the SUN Project. Eur J Clin Nutr 2012; 66: 360–368.
Sofi F, Cesari F, Abbate R, Gensini GF, Casini A . Adherence to Mediterranean diet and health status: a meta-analysis. BMJ 2008; 337: a1344.
Trichopoulou A, Costacou T, Bamia C, Trichopoulos D . Adherence to Mediterranean diet and survival in a Greek population. N Engl J Med 2003; 348: 2599–2608.
The author declares no conflict of interest.
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Kepler, S. Adherence to the Mediterranean diet and quality of life in the SUN Project. Eur J Clin Nutr 66, 975 (2012). https://doi.org/10.1038/ejcn.2012.74