Abstract
Background
The effects of Mediterranean diets (MED) on various health parameters suggest potential cardiovascular (CV) health benefits.
Purpose
We evaluated the effects of MED for primary prevention of CV risk factors and disease in overweight or obese adults.
Methods
A systematic review and meta-analysis of randomized controlled trials (RCTs) was performed using PRISMA guidelines. PubMed, EMBASE, Web of Science, Scopus, Cochrane Library, clinicaltrials.gov, and clinicaltrialsregister.eu were searched until January 2020. RCTs evaluating any type of MED compared to other diets or advice in adults were included. Predefined CV risk factors were lipid, liver, glucose, anthropometric, and blood pressure outcomes. Clinical outcomes were all cause mortality, CV mortality, myocardial infarction (MI), coronary artery disease, stroke, cerebrovascular disease, and diabetes. Meta-analyses of random effects models were performed and effects were described as mean difference (MD) and their 95% confidence intervals (CI). Subgroup analyses by weight, type of MED, type of control, and trial duration were performed when heterogeneity was high (I2>60%).
Results
Eighteen RCTs (n=915) were included. Two RCTs evaluated only obese patients, 13 evaluated overweight and obese patients, and three did not specify. Fifteen RCTs evaluated MED alone while three evaluated MED combined with another diet. Thirteen RCTs evaluated effects of another diet while five evaluated diet advice or no treatment as controls. The median time to follow up was 6 months (range 6 weeks to 24 months). Clinical outcomes were only described in the revised 2018 PREDIMED trial where MED were associated with 35% lower risk of MI, stroke, and CV death vs advice (HR 0.65, 95% CI 0.50 to 0.85). MED were significantly associated with lower levels of triglycerides (TG) (MD −12.70 mg/dL, 95% CI −18.58 to −6.82), waist circumference (WC) (MD −1.92 cm, 95% CI −3.59 to −0.24), weight (MD −1.75 kg, 95% CI −2.82 to −0.69), and body mass index (BMI) (MD −0.69 kg/m2, 95% CI −1.11 to −0.27), and higher levels of HDL (MD 2.03 mg/dL, 95% CI 1.13 to 2.92) compared to other diets or advice. MED did not significantly change any other CV risk factors. Subgroup analyses showed some differences vs main analyses, but were based on a small set of RCTs in most of cases. Excluding five high risk of bias RCTs showed significant reductions in total cholesterol (MD −6.57 mg/dL, 95% CI −12.22 to −0.93), Fatty Liver Index (MD −23.30, 95% CI −30.20 to −16.40), HOMA-IR (MD −0.53, 95% CI −1.02 to −0.05), and SBP (MD −2.35 mmHg, 95% CI −4.02 to −0.68).
Conclusion
MED significantly decreased TG and anthropometric outcomes, and increased HDL when compared to other diets or advice. There was no significant association between MED and the other predefined CV risk factors. Newer RCTs without the flaws of PREDIMED are needed to further evaluate clinical outcomes.
Funding Acknowledgement
Type of funding source: None
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