What makes the Mediterranean diet work?

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It’s been nearly 30 years since researchers first recognized the health benefits of the Mediterranean diet, which is characterized by high consumption of vegetables, fruits, nuts, legumes, cereals, seafood and olive oil, along with a moderate amount of alcohol and relatively little meat and dairy. But apparently, they’ve never tried to figure out which of those components deserves the credit.

Now researchers from the University of Athens Medical School in Greece and the Harvard School of Public Health have examined the relative contribution of each of these foods and determined that moderate alcohol consumption plays the biggest role in reducing mortality. The results were published online Tuesday in the British Medical Journal.

The team analyzed dietary data collected from 23,349 Greeks 20 to 86 years old who filled out food surveys and were followed for an average of 8.5 years. Researchers controlled for factors such as age, sex, smoking status, amount of exercise and BMI.

Overall, they confirmed that people who ate a Mediterranean diet were healthier than those who didn’t. There were 652 deaths among the 12,694 people who didn’t follow the diet closely (a mortality rate of 5%) compared with 423 deaths among the 10,655 who did (for a 4% mortality rate).

Alcohol alone accounted for 24% of the total benefit, the researchers found. Most of that came in the form of wine consumed with meals.

Unlike with alcohol, none of the foods was associated with health outcomes in a statistically significant way – that is, the differences observed could have been due to chance. However, the researchers churned through the data and calculated that low meat consumption was responsible for 17% of the upside of following a Mediterranean diet. That was followed by 16% from high consumption of vegetables and 10% to 11% each from eating lots of fruits and nuts, olive oil and legumes. The amount of cereals, dairy products and seafood eaten didn’t appear to make much difference.

-- Karen Kaplan