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WHEN it comes to healthier diets, one of them has always had a have-your-cake-and-eat-it feel. For decades, we have been told that the secret to staying well is to indulge in the delicious fresh foods of the Mediterranean. Adding more tomatoes, focaccia and olive oil to your dinner plate – and washing it down with a glass of chianti – is claimed to be a great way to reduce your odds of having a heart attack or developing type 2 diabetes.

Most surprising of all, this isn’t just overhyped nonsense. Evidence has been mounting for over 50 years that the Mediterranean diet really can improve your health in many ways. “We have long-term, large clinical trials with hard clinical events as the outcomes,” says at the University of Navarra in Pamplona, Spain.

And not many diets get a UNESCO listing. A decade ago, this United Nations body .

But despite all this praise, figuring out what it is about the diet that leads to such benefits has been tricky. For starters, nutritionists can’t agree on the exact form it should take. And then there are factors like eating as a family, cooking at home and other non-dietary elements that must be considered. The good news is that, over the past decade, we have begun to learn which components of the diet offer the biggest health benefits and why. This means we are closer than ever to offering the best advice on eating well, even for those who will never reside in the beautiful Mediterranean countryside themselves.

What is the Mediterranean diet?

The Mediterranean diet owes its fame to US physiologist Ancel Keys and his wife Margaret, a chemist turned nutritionist. In , Ancel became one of the first to argue that saturated fats – mostly found in animal products like meat and dairy – are a because they lead to a build-up of cholesterol in the blood. He said that unsaturated fats, which are more common in plant products and fish, are a healthier alternative.

Building on this, the couple travelled the world to study the diets people ate in different regions. The result was the , which began in 1956 and compared diet and health in parts of the US, Japan, Finland, the Netherlands, Italy, Greece and what was then Yugoslavia. The research consistently offered evidence for the link between eating unsaturated fat and a reduced risk of heart disease – .

So far, so predictable. But during their work, Ancel and Margaret noticed something else. In one of their study areas – southern Italy – there were a surprisingly large number of centenarians. The pair became convinced that details of the local diet, which was high in unsaturated fat, were the key to this longevity. , later even . The fact that both of them went on to live long lives – ; Margaret followed two years later, – just seemed to add further credence to their message. The Mediterranean diet became increasingly popular.

What foods are included?

But along the way, confusion began to arise about exactly what it comprises. One thing at least is clear: it doesn’t feature large quantities of the more indulgent foods of Italy, Greece and Turkey, such as lasagne, moussaka, pizza and kofta kebabs. In fact, many people in the region don’t eat the version of the diet that has been tied to health benefits.

One of the most widely used definitions of what it should include is the . This was developed in the 1990s by Antonia Trichopoulou, then at the National School of Public Health in Athens, Greece. An . According to the MDS, a fully Mediterranean diet is one containing lots of vegetables, legumes, fruits and nuts, cereals and a moderately high amount of fish. It also contains little meat, poultry and dairy – and, perhaps surprisingly, it includes a moderate amount of alcohol, typically red wine.

“This is the most commonly used definition,” says Martínez-González. However, he and his team developed an alternative in 2011 called the that also considers the use of olive oil in cooking (desirable) and the consumption of fizzy or sugary drinks (undesirable).

Other changes to the standard definition of the diet have as researchers have continued to refine their understanding of the optimal form it should take for a prolonged healthy life. “Dairy is considered neutral now,” says at the University of Hertfordshire in the UK. The amount of alcohol recommended has gone down too, he adds. But as a result of this constant tweaking and redefining, “there is no formal consensus” on the exact profile of the diet, says Martínez-González.

Even if the precise list of foodstuffs is up for debate, a series of large-scale and long-term studies have broadly confirmed Ancel and Margaret’s hunch that a generalised version of it carries health benefits.

“The best evidence is for cardiovascular disease,” says Hoffman. “The Mediterranean diet is generally considered to be the best dietary intervention to prevent somebody getting a heart attack or a stroke.” For instance, in 2022, a study called CORDIOPREV suggested that following the Mediterranean diet rather than a generalised low-fat diet leads to a in people who have already had one.

Cardiovascular disease protection

There is also evidence that the diet reduces the risk of developing cardiovascular disease in the first place. A 2020 review by Cochrane, a UK charity that examines evidence on health issues, looked at 22 randomised controlled trials investigating this issue and found “” that the diet reduced cardiovascular risk factors. A comprehensive overview published the following year by a pair of researchers at Harvard University found .

These protective properties are what some researchers use to explain why the rate from cardiovascular disease in Italy is far below the global average: they argue that enough people in the country follow the diet to substantially affect the statistics.

The benefits seem to extend beyond cardiovascular disease. A 2020 review concluded that people who follow the diet are than those who don’t. It has also been suggested that the , including , although more evidence is needed to confirm the link.

While some of these purported benefits may disappear as more rigorous studies are conducted, Martínez-González is confident that the diet is still worth adopting. “No study that I know has shown a harm of the Mediterranean diet,” he says.

At this point, you may be preparing to dash to the shops to buy some aubergines and pine nuts, but hang on. It seems the Mediterranean diet doesn’t work for everyone.

One of the biggest investigations of this way of eating is the , which follows over 20,000 people who were recruited in southern Italy between 2005 and 2010. In a 2018 update, researchers led by at IRCCS NEUROMED, a neurological institute in Pozzilli, Italy, found what seemed, at first, like a . Based on 4.3 years of data, people who followed the Mediterranean diet were less likely to experience cardiovascular health problems.

However, there was a twist. The benefits were only seen in highly educated people and those with high household incomes. “If you belong to a low-educated group or to a low-income group, this protection was not seen,” says Bonaccio.

Why would people with lower household incomes or a lower educational status not get the same health benefits as wealthy and highly educated people?

One possibility is that the details of what people eat really matter, says Bonaccio. “We ask people, for example, how many fruits you eat per day,” she says. But studies don’t ask about the type of fruit, how it was grown or the form it took. The quality of the food, she suggests, may play a role. This would fit the data: people from lower-income households may have little choice but to buy and eat cheaper frozen or processed foods, which may not be as nutritious as fresh foods. However, finding out if this is the real explanation would require finer-grained studies of what people are eating.

With that in mind, researchers are now focusing on how specific components of the Mediterranean diet may account for its health benefits. One ingredient in particular is emerging as key: extra-virgin olive oil. “The Mediterranean diet is the diet of the countries that grow olive trees,” says Bonaccio.

Olive oil producers press and grind fresh olives to release the oil, which is actually derived from the fruit, says Hoffman. This makes it unlike other oils that come from seeds and have to be extracted using chemicals and high temperatures. Extra-virgin olive oil, which tends to have a darker colour, is in a way that would alter the oil.

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“The Mediterranean diet is far more effective if it includes extra-virgin olive oil,” says Hoffman. For instance, a review published in June 2023 found that , higher levels of “good” cholesterol and lower levels of “bad” cholesterol.

The oil is rich in the unsaturated fats that were championed decades ago by Margaret and Ancel Keys. But there is growing evidence that its health benefits are that are . These include a host of plant chemicals, one notable kind being polyphenols. The June review concluded that polyphenols were probably responsible for extra-virgin olive oil’s benefits. In line with this, a study published in February 2023 found that in a way that seemed to prompt the rodents to develop significantly lower blood pressure in their arteries as their hearts beat than mice that were fed a standard mouse diet or a mouse diet enriched in either butter or refined olive oil.

It isn’t just the microbiome that might be implicated in the health benefits of extra-virgin olive oil. Personal genetics may play a role too, given evidence that may influence the activity of genes linked to things like inflammation. It has even been suggested that, as we learn more about this tie-up between nutrition and genetics, it may be possible to recommend .

So where does all this leave anyone eager to benefit from the Mediterranean diet? Some researchers aren’t convinced it is for everyone. They think that, as we have learned more about what is going on, it has become increasingly unclear whether the diet can be made to work beyond the Mediterranean itself. For instance, Bonaccio says we now know that each world region is characterised by distinctive features, like climate and microbes, that alter the local optimal diet. “I believe that each country should discover its own traditional diet that can protect them from diseases and help them to live longer,” she says.

Others are more optimistic about the Mediterranean diet’s broad applicability – although they argue that it is most important to replicate its general features rather than its specifics.

“You don’t need to be eating Mediterranean vegetables like peppers and aubergines,” says Hoffman. “You can be eating northern European vegetables like cabbages and carrots, and that counts just as much.”

Some components, like extra-virgin olive oil, would appear non-negotiable, however: Hoffman stresses its importance. But, of course, encouraging people to buy this key ingredient is tough at a time when .

Martínez-González wants to see taxes introduced on ultra-processed fare like sodas and fast food, and for the revenues to be used to subsidise healthier options. The improvements to public health that better-quality diets should bring would cut the costs of medical care. “If the governments do that, they will save money at the end of the day,” he says.

However, even for those who can afford to purchase high-quality foods, there is one potentially vital component of the diet that can’t be found on supermarket shelves. It is possible that some of the reported benefits of the diet aren’t due to the food itself, but to the associated lifestyle. Bonaccio points out that the Mediterranean villagers studied by Ancel and Margaret Keys – and later by Trichopoulou – didn’t just eat a specific diet, “they also had a specific way of living”. For instance, they resided in the countryside and their work was often outdoors and physical. Other studies show such factors make a difference: research published in March 2023 found that walking just an extra 500 steps a day reduces the risk of cardiovascular disease in older adults. Strength training is particularly effective at lowering this risk.

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It is probably also significant that the Mediterranean villagers studied in the 20th century prepared their own food and often ate leisurely meals in social groups – which some research suggests boosts general happiness and life satisfaction, both of which are also linked to better health. “You cannot do the Mediterranean diet without cooking,” says Bonaccio.

Unless we can find the time to prepare our own meals and savour them with friends, we may never feel the full effects of the Mediterranean diet. But carve out those extra hours each day for such dining, while also remaining active, and it might be possible for all of us to experience the health benefits that so impressed Ancel and Margaret on their . You could call it having your focaccia and eating it.

Michael Marshall is a science writer based in Devon, UK, and author of The Genesis Quest

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