Efficacy of Mediterranean diet for the primary prevention of oncological diseases: A systematic review and meta-analysis featured in the Italian National Guidelines "La Dieta Mediterranea".

[BACKGROUND] The Mediterranean diet (MD), characterized by high consumption of plant-based foods, olive oil, moderate intake of fish and poultry, and limited red and processed meats, has been associated with various health benefits, but its role in cancer prevention remains under debate.

[METHODS] This review was conducted in accordance with PRISMA 2020 and MOOSE guidelines. A comprehensive search of PubMed/MEDLINE, Scopus, Embase, and Cochrane Library was performed up to February 28, 2024. Study quality was assessed using the Newcastle-Ottawa Scale, and the certainty of evidence was evaluated with the NUTRIGRADE approach. Pooled effect sizes were computed using a random-effects model and expressed as risk ratios (RR), hazard ratios, or odds ratios, as appropriate.

[RESULTS] A total of 126 studies, including more than 8 million participants, across all included studies, were included. High adherence to the MD, as one point increase in the adherence, was significantly associated with a modest reduced risk of several site-specific cancers, including head and neck (RR = 0.88, 95% CI 0.78-0.98), oral cavity (RR = 0.83, 95% CI 0.73-0.95), stomach (RR = 0.93, 95% CI 0.88-0.97), liver/gallbladder (RR = 0.94, 95% CI 0.93-0.96), colorectal (RR = 0.95, 95% CI 0.92-0.98), bladder (RR = 0.96, 95% CI 0.92-0.995), and breast cancer (RR = 0.95, 95% CI 0.92-0.98). Higher adherence was also associated with lower cancer-related mortality (RR = 0.97, 95% CI 0.96-0.99). Certainty of evidence was rated as moderate for the main outcomes.

[CONCLUSIONS] Greater adherence to the MD is associated with a lower risk of several site-specific cancers and reduced cancer mortality. These findings support the promotion of the MD as a preventive dietary strategy within public health policies.