Study Finds Mediterranean Diet May Reduce Risk of Certain Cancers

Led by Zoltan Ungvari from the University of Oklahoma Health Sciences Center and Semmelweis University, researchers reviewed 34 observational studies sourced from databases like PubMed, Web of Science, and Scopus, focusing on publications until September 2025. From an initial examination of 12,530 records, the team refined the studies to those that measured adherence using validated methods and provided quantitative risk estimates for the three cancers in question. The final dataset comprised 4,286,835 participants, making it one of the largest investigations into diet and these specific cancers.

The analytical methodology was conservative, employing random-effects models to capture the variability between studies. For head and neck cancer, 14 cohorts indicated a pooled relative risk of 0.55, with a confidence interval of 0.45 to 0.67. Similarly, 13 studies focused on gastric cancer yielded a pooled relative risk of 0.62 (95 percent CI 0.53 to 0.73), while 11 studies regarding liver cancer reported a relative risk of 0.59 (95 percent CI 0.53 to 0.67). All findings were statistically significant, as the confidence intervals excluded the null value of 1.0.

However, the analysis noted substantial variability in results, particularly for head and neck cancer, which had an I-squared value of 90 percent—indicating that a significant portion of the variability stemmed from true differences among study outcomes. Gastric cancer also exhibited high heterogeneity at 76 percent, while the liver cancer results were more consistent, with only moderate heterogeneity of 35 percent. This consistency suggests a robust protective association for liver cancer across different study populations and methods.

The findings introduced complexities regarding potential bias, particularly for head and neck and gastric cancers, where indications of publication bias or small-study effects were observed. The authors chose not to make adjustments for these biases, pointing out that genuine differences across studies could also account for the funnel plot asymmetry.

The study theorizes that the Mediterranean diet may influence such disparate cancers due to underlying biological mechanisms. Chronic inflammation and oxidative stress are known to promote carcinogenesis in the digestive tract and upper aerodigestive system. The Mediterranean diet is rich in compounds that counteract these effects, including fiber and omega-3 fatty acids. For liver cancer specifically, improving insulin sensitivity and reducing fatty liver disease are notable benefits of this dietary pattern.

Furthermore, the gut microbiome is influenced by a diet high in plant-based foods, contributing to improved intestinal health and potentially impacting gastrointestinal malignancies. The authors underscore that these same biological pathways intersect with aging, suggesting that adhering to the Mediterranean diet may impact both cancer risk and age-related diseases.

The study highlights methodological limitations, particularly reliance on self-reported dietary assessments, which may lead to measurement errors. Although the benefits are notable, the authors advise caution in interpreting the data due to potential confounding factors, such as lifestyle behaviors commonly associated with those who follow the Mediterranean diet.

The public health implications are significant. Given its beneficial effects on various health outcomes, the Mediterranean diet could serve as a cost-effective strategy for preventing not only gastrointestinal cancers but also other chronic diseases prevalent in regions like Central and Eastern Europe, where cancer mortality rates are high. The authors advocate for further research involving larger prospective cohorts to strengthen the link between Mediterranean diet adherence and cancer risk reduction.