The Mediterranean diet, named after the region that inspired it, has long been associated with better health.

Now a new study highlights a 23 percent reduction in mortality rates in women following the diet, providing even more evidence of the benefits that come with swapping processed foods for fresh fruit and vegetables.

Records of 25,315 women followed over 25 years showed that those whose eating habits regularly matched the Mediterranean model were more than a fifth less likely to die of any cause over the study period, compared with those not following the diet.

What's more, the research team from Brigham and Women's Hospital (BWH), a part of Harvard Medical School, was able to identify biological changes that may explain why the Mediterranean diet is associated with longevity.

"For women who want to live longer, our study says watch your diet," says cardiologist Samia Mora, from BWH.

"The good news is that 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 US and globally."

A Mediterranean diet is largely based on nuts, seeds, fruits, vegetables, whole grains, and legumes, with olive oil as a primary fat source. Proteins can come from small amounts of fish, poultry, dairy, and eggs. Red meat, processed foods, and alcohol are kept to a minimum.

The researchers looked at numerous biomarkers in the body, finding that the main benefits of the diet seemed to be in metabolic and inflammatory processes in the body – those processes helping to keep bodily functions running normally.

There were also improvements in blood pressure and insulin resistance in those on a Mediterranean diet, compared to those with other eating habits. It appears that all these multiple factors add up to protect against an early death.

"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," says epidemiologist Shafqat Ahmad from BWH and Uppsala University in Sweden.

It's important to keep in mind that the study involved mainly white, non-Hispanic, middle aged and older women, who were all well educated health professionals. Aside from the biomarker analysis, the data was collected through self reporting, while the method wasn't designed to determine cause and effect.

However, the large sample size and the long follow-up period, together with other studies in this area pointing to similar conclusions, suggest that the Mediterranean diet really might help us live longer – and we're beginning to understand why.

"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," says Mora.

"Public health policies should promote the healthful dietary attributes of the Mediterranean diet and should discourage unhealthy adaptations."

The research has been published in JAMA Network Open.