If there's a single way of eating that persists in laying claim as one of the healthiest, it's the Mediterranean diet. Experts continue to sing its praises.
And the number of positive studies over the years makes it hard to argue with them.
The Mediterranean diet isn't a specific diet plan per se, but rather eating in the traditional style of those living in Mediterranean countries. It's characterized by consuming a lot of vegetables, fruits, nuts, legumes and unrefined grains. There is plenty of olive oil, but little saturated fat; a moderate intake of fish, but little dairy, meat and poultry. And while cookies and sugar are limited, a regular but moderate dose of wine is involved.
Why you hear so much about it
Researchers have been uncovering the benefits of this particular diet for years. In fact, the diet's benefits for heart health were so clear in one study published in the New England Journal of Medicine that researchers ended the study early, saying it was unethical to continue.
That groundbreaking paper was retracted, however, by the New England Journal of Medicine in June 2018 because of the way the study was carried out. The authors of the original paper replaced it with a corrected one published in the New England Journal of Medicine that softened its language about how the diet might prevent heart attacks and strokes, NPR notes.
But a change in one high-profile paper doesn't mean researchers have changed their stance on the diet.
"I don't know anybody who would turn around from this and say, 'Now that this has been revealed, we should all eat cotton candy and turn away from the Mediterranean diet,'" David Allison, dean of the School of Public Health at Indiana University in Bloomington, tells NPR.
The Mediterranean diet and telomere length
Scientists in Boston looked at the nutritional data from 4,676 women participating in the Harvard Nurses' Health Study — the well-known ongoing prospective cohort analysis — and discovered that those whose food choices most closely followed a Mediterranean diet had longer telomeres. Telomeres are the protective buffers on the ends of chromosomes and can be used as a biomarker of aging; the longer they are, the better.
"We know that having shorter telomeres is associated with a lower life expectancy and a greater risk of cancer, heart disease and other diseases," said study coauthor Immaculata De Vivo, an associate professor of medicine at Brigham and Women's Hospital. "Certain lifestyle factors like obesity, sugary sodas, and smoking have been found to accelerate telomere shortening, and now our research suggests the Mediterranean diet can slow this shortening."
Their research was published in The BMJ.
It's thought that the antioxidants present in the favored foods protect against cell aging. While the researchers didn't find that any specific food provided the silver bullet, they suggest it was a combination of the components that predicted telomere length.
The researchers scored each woman's diet according to how closely it adhered to Mediterranean components. What they found was that each one-point change in their grading system equated to an extra year and a half of life. A three-point change, the study notes, would correspond to an average 4.5 years of aging, which is comparable to the difference between smokers with non-smokers.
The researchers also concluded that women who may have veered slightly from the Mediterranean diet but who still ate a healthy diet — like eating chicken and low-fat dairy products in addition to the Mediterranean basics — also had longer telomeres than those who ate a standard American diet with red meat, saturated fats, sweets and empty calories. Those who followed the Mediterranean diet, however, had the longest telomeres on average.
Mediterranean diet and brain health
In a 2020 study, researchers found that the Mediterranean diet was also associated with higher cognitive function.
For the study, researchers at the National Eye Institute, part of the National Institutes of Health, analyzed data from two major eye disease studies. Those clinical trials had investigated the effects of diet on age-related macular degeneration (AMP), an eye disease that damages the retina and can lead to blindness.
They found that certain components of the diet were associated with a lower risk of developing AMP. They wanted to see if the nutritional aspects of the diet had any similar impact on cognition.
Researchers analyzed data from 7,756 people who had taken part in the clinical trials for a decade. As part of their participation, they had completed cognitive tests during that time and answered detailed questions about their diet.
Researchers found that study participants adhering closest to the Mediterranean diet — particularly with high fish and vegetable consumption — had the lowest risk of cognitive impairment. The study, published in Alzheimer's & Dementia, found no link between diet and cognitive decline.
"We do not always pay attention to our diets. We need to explore how nutrition affects the brain and the eye," the study's lead author Emily Chew, M.D., director of the NEI Division of Epidemiology and Clinical Applications, said in a statement.
Mediterranean diet and gut health
Another study found that eating a Mediterranean diet causes microbiome changes linked to improvements in cognitive function and memory, immunity and bone strength, according to the study authors, writing about their work for The Conversation.
The researchers, who published their work in Gut, a BMJ journal, looked at the diets of 612 people aged 65-79, from the United Kingdom, France, the Netherlands, Italy and Poland. Half of the group changed their diet to a Mediterranean diet for a full year and other half continued to ear their normal diet. They didn't initially see that many differences, but over time, two patterns emerged in those who followed the Mediterranean diet: an increase in what they dubbed diet-positive microbes — those linked to less inflammation and less frailty overall — and a decrease in diet-negative microbes, which was also associated with better health. The researchers suggest this means the diet not only changed the participants' health; it also changed the participants' microbiome in a way that had more far-reaching affects.
"When we compared the changes in the number of these microbes in the treatment group (those on the Mediterranean diet) and the control group (those following their regular diet), we saw that the people who strictly followed the Mediterranean diet increased these diet-positive microbes. Although the changes were small, these finding were consistent across all five countries — and small changes in one year can make for big effects in the longer term."
Editor's note: This story was originally published in December 2014 and has been updated with new information.