Methodologic quality of meta-analyses and systematic reviews on the Mediterranean diet and cardiovascular disease outcomes: A review

Background: Several systematic reviews/meta-analyses published within the past 10 y have examined the associations of Mediterranean- style diets (MedSDs) on cardiovascular disease (CVD) risk. However, these reviews have not been evaluated for satisfying contemporary methodologic quality standards. Objective: This study evaluated the quality of recent systematic reviews/meta-analyses on MedSD and CVD risk outcomes by using an established methodologic quality scale. The relation between review quality and impact per publication value of the journal in which the article had been published was also evaluated. Design: To assess compliance with current standards, we applied a modified version of the Assessment of Multiple Systematic Reviews (AMSTAR_MedSD) quality scale to systematic reviews/meta-analyses retrieved from electronic databases that had met our selection criteria: 1) used systematic or meta-analytic procedures to review the literature, 2) examined MedSD trials, and 3) had MedSD interventions independently or combined with other interventions. Results: Reviews completely satisfied from 8% to 75% of the AMSTAR_MedSD items (mean ± SD: 31.2% ± 19.4%), with those published in higher-impact journals having greater quality scores. At a minimum, 60% of the 24 reviews did not disclose full search details or apply appropriate statistical methods to combine study findings. Only 5 of the reviews included participant or study characteristics in their analyses, and none evaluated MedSD diet characteristics. Conclusions: These data suggest that current meta-analyses/systematic reviews evaluating the effect of MedSD on CVD risk do not fully comply with contemporary methodologic quality standards. As a result, there are more research questions to answer to enhance our understanding of how MedSD affects CVD risk or how these effects may be modified by the participant or MedSD characteristics. To clarify the associations between MedSD and CVD risk, future meta-analyses and systematic reviews should not only follow methodologic quality standards but also include more statistical modeling results when data allow.