The role of the Mediterranean diet in cardiovascular disease prevention

By Dr. Sushama R. Chaphalkar, PhD.Reviewed by Benedette Cuffari, M.Sc.Aug 21 2024

In a recent study published in Nutrition & Dietetics, researchers performed an updated review of recent studies to evaluate the effectiveness of the Mediterranean Diet (MedDiet) in preventing cardiovascular disease (CVD).

Study: The effectiveness of the Mediterranean Diet for primary and secondary prevention of cardiovascular disease: An umbrella review. Image Credit: JeniFoto / Shutterstock.com

The health benefits of the MedDiet

CVD is a leading cause of death worldwide. Primary prevention of CVD involves diet and lifestyle factors to prevent disease onset, whereas secondary prevention aims to minimize disease impact through early diagnosis.

The MedDiet has been recognized for its effectiveness in both primary and secondary prevention of CVDs since the 1950s. This diet is characterized by the high consumption of olive oil, fruits, nuts, vegetables, legumes, and fish, moderate intake of wine and dairy, and low consumption of meat.

Several studies have reported the inverse association between the MedDiet and CVD outcomes. In fact, several randomized controlled trials (RCTs) have reported significant reductions in cardiovascular events among those following the MedDiet; however, these studies have been associated with methodological limitations.
Although there is evidence supporting the benefits of the MedDiet, most systematic reviews have not focused exclusively on RCTs. Furthermore, there is a need for updated reviews that consider the latest evidence.

About the study

In the present umbrella review, researchers examine systematic reviews of RCTs that assessed the impact of MedDiet on the primary and secondary prevention of CVD as compared to other diets or no intervention. Various outcomes, including mortality, cardiovascular events, and CVD risk factors, were considered while also evaluating the quality and certainty of the evidence in these reviews.

The Cochrane Database of Systematic Reviews, PubMed, Embase, ProQuest, and Cumulative Index of Nursing and Allied Health Literature were searched. Based on predefined criteria, systematic reviews up to November 2022 were selected.

The analysis included 18 systematic reviews and 238 RCTs that compared the MedDiet with other diets. Some of these included low fat, Atkin’s diet, dietary approaches to stop hypertension, low carbohydrate diets, no intervention, or usual care in 197,965 participants. The RCTs were conducted in various countries, both within and outside the Mediterranean region.

Data extraction and quality assessments were conducted using the Assessment of Multiple Systematic Review 2 (AMSTAR-2) tool. The certainty of evidence was evaluated with Grading of Recommendations, Assessment, Development, and Evaluations (GRADE) tool.

The researchers synthesized meta-analytic results, focusing on outcomes such as all-cause mortality, cardiovascular events, and CVD risk factors. To assess redundancy, the overlap of primary studies across systematic reviews was calculated.

Study findings

The overlap of primary studies across the systematic reviews was 8%, thus indicating moderate redundancy. About 61% of the reviews were of critically low quality, 22% were of low quality, and 17% were of moderate quality. None of the reviews were considered to be of high quality.

Thirteen reviews focused on the primary prevention of CVDs, whereas others included both primary and secondary prevention. One review suggested low-certainty evidence that the MedDiet reduced all-cause mortality by about 50% in those with a history of CVDs but not in those without CVDs.

Four reviews indicated that the MedDiet might reduce CVD-related mortality by 10-65%; however, the evidence for this observation was of low to moderate certainty. Findings on cardiac-related mortality were inconsistent, with some reviews reporting reductions in fatal myocardial infarction and sudden cardiac death with varying certainty levels.

Non-fatal CVD outcomes, such as heart failure and coronary events, also showed reductions; however, the evidence was similarly of low to moderate quality. Stroke incidence was consistently reduced by 35-42% across several reviews.

In most reviews, the MedDiet was associated with reductions in both systolic and diastolic blood pressure by one to five mmHg; however, the quality of the evidence varied. Five reviews found that the MedDiet lowered glycated hemoglobin levels in adults with type 2 diabetes; however, these reviews were mostly of critically low quality.

Despite their low certainty, four of seven reviews reported that the MedDiet reduced low-density lipoprotein cholesterol (LDL-C) levels. Only one review found a statistically significant reduction in body mass index (BMI) values with the MedDiet; however, the evidence was of low certainty.

Conclusions

Although the MedDiet is associated with potential benefits in reducing both fatal and non-fatal cardiovascular outcomes, many of the systematic reviews supporting these claims were of low methodological quality. Therefore, further research and stronger evidence are needed to support the potential clinical application of MedDiet to prevent CVDs and improve public health outcomes.