In a study that followed more than 25,000 U.S. women for up to 25 years, researchers from Harvard-affiliated Brigham and Women’s Hospital found that participants who closely followed the Mediterranean diet had up to a 23 percent lower risk of all-cause mortality, with benefits for both cancer and cardiovascular health. The researchers found evidence of biological changes that may help explain the longevity gains. Results are published in JAMA.

“For women who want to live longer, our study says watch your diet,” said senior author Samia Mora, a cardiologist and a professor of medicine at Harvard Medical School. “Following a Mediterranean dietary pattern could result in about one-quarter reduction in risk of death over more than 25 years with benefit for both cancer and cardiovascular mortality, the top causes of death in women and men in the U.S. and globally.”

The Mediterranean diet is rich in plants (nuts, seeds, fruits, vegetables, whole grains, legumes). The main fat is olive oil, usually extra-virgin. The regimen includes moderate intake of fish, poultry, dairy, eggs, and alcohol, and rare consumption of meats, sweets, and processed foods.

The authors of the current study investigated the long-term benefit of adherence to a Mediterranean diet in a U.S. population recruited as part of the Women’s Health Study, and illuminated biological mechanisms that may explain the diet’s health benefits. Investigators evaluated a panel of approximately 40 biomarkers representing various biological pathways and clinical risk factors.

Biomarkers of metabolism and inflammation were most important, followed by triglyceride-rich lipoproteins, adiposity, and insulin resistance.

“Our research provides significant public health insight: Even modest changes in established risk factors for metabolic diseases — particularly those linked to small-molecule metabolites, inflammation, triglyceride-rich lipoproteins, obesity, and insulin resistance — can yield substantial long-term benefits from following a Mediterranean diet,” said lead author Shafqat Ahmad, an associate professor of epidemiology at Uppsala University Sweden and a researcher in the Center for Lipid Metabolomics and the Division of Preventive Medicine at the Brigham.

The authors noted some key limitations of the study, including that it was limited to middle-aged and older, well-educated female health professionals who were predominantly non-Hispanic and white. The study relied on food-frequency questionnaires and other self-reported measures, such as height, weight, and blood pressure. But the study’s strengths include its large scale and long follow-up period.

The authors also note that as the concept of the Mediterranean diet has gained popularity, the diet has been adapted in different countries and cultures.

“The health benefits of the Mediterranean diet are recognized by medical professionals, and our study offers insights into why the diet may be so beneficial,” said Mora. “Public health policies should promote the healthful dietary attributes of the Mediterranean diet and should discourage unhealthy adaptations.”

The Women’s Health Study is supported by the National Institutes of Health. More information on funding for individual researchers here.

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