Effect of Mediterranean Diets on Cardiovascular Risk Factors and Disease in Overweight and Obese Adults: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

We systematically evaluated effects of Mediterranean diets (MED) on cardiovascular (CV) disease and risk factors in overweight or obese adults. Five engines and two registries were searched until October 2023 for randomized controlled trials (RCTs) evaluating any type of MED compared to other diets or advice in adults. Outcomes of interest were clinical outcomes and CV risk factors (anthropometric, lipids, blood pressure, glucose metabolism, liver function). Inverse variance random effects models were used for meta-analyses; effects of MED were described as mean differences (MDs) and their 95% confidence intervals (CIs). Quality of evidence (QoE) per outcome was evaluated using GRADE methodology. Twenty-six RCTs (n = 10,352) were included. Four RCTs evaluated only obese patients and 22 evaluated overweight and obese patients. Clinical outcomes were only described in the revised 2018 PREDIMED trial where MED was associated with 35% lower risk of myocardial infarction, stroke, or CV death vs advice (hazard ratio, 0.65; 95% CI, 0.50-0.85). MED significantly reduced the values of body mass index (MD, -0.61 kg/m²; 95% CI, -1.14 to -0.09; 17 RCTs), waist circumference (MD, -2.48 cm; 95% CI, -3.99 to -0.96; 17 RCTs), triglycerides (MD, -7.93 mg/dL; 95% CI, -13.48 to -2.39; 19 RCTs), and fatty liver index (MD, -12.26; 95% CI, -23.96 to -0.56; 3 RCTs) compared with controls. MED did not significantly change any other CV risk factors. QoE was very low for most of the outcomes; 85% of RCTs had some concerns or high risk of bias. In overweight or obese adults, MED significantly decreased body mass index, waist circumference, triglycerides, and fatty liver index score but no other CV risk factors when compared with other diets or advice. There was paucity of data on effects of MED on clinical outcomes.