Cochrane corner: does the Mediterranean-style diet help in the prevention of cardiovascular disease?

Key components of a Mediterranean dietary pattern are a high monounsaturated/saturated fat ratio (use of olive oil as main cooking ingredient and/or consumption of other traditional foods high in monounsaturated fats such as tree nuts) and a high intake of plant-based foods, including fruits, vegetables and legumes.2 Despite the consistent observational data, the trial evidence on the effectiveness of a Mediterranean-style diet in the prevention and management of major CVD is relatively limited or of questionable quality. Definitions of a Mediterranean dietary pattern vary, hence we included only RCTs of interventions that reported at least both of the following key components: a high monounsaturated/saturated fat ratio (use of olive oil as main cooking ingredient and/or consumption of other traditional foods high in monounsaturated fats such as tree nuts) and a high intake of plant-based foods, including fruits, vegetables and legumes.2 The control group received no intervention or minimal intervention, usual care or another dietary intervention. There was a high degree of heterogeneity across trials in terms of participants recruited and the range of dietary interventions. [...]we grouped studies into the following four categories to facilitate our interpretation of the results: (1) Mediterranean dietary intervention compared with no intervention or a minimal intervention for primary prevention; (2) Mediterranean dietary intervention compared with another dietary intervention for primary prevention; (3) Mediterranean dietary intervention compared with usual care for secondary prevention and (4) Mediterranean dietary intervention compared with another dietary intervention for secondary prevention. The PREDIMED trial (7747 randomised) was retracted and re-analysed following concerns regarding randomisation at 2 of 11 sites.4 Low-quality evidence showed little or no effect of the PREDIMED intervention (advice to follow a Mediterranean diet plus supplemental extra virgin olive oil or tree nuts) compared with a low fat diet on CVD mortality (HR 0.81 (95% CI 0.50 to 1.32)) or total mortality (HR 1.00 (95% CI 0.81 to 1.24)) over 4.8 years.