The Mediterranean diet has held the top spot on the U.S. News & World Report ranking of best diets for eight consecutive years. That is a remarkable run for an eating pattern that was described as “the Mediterranean diet” for the first time only in 1975, by the American physiologist Ancel Keys and his wife Margaret, in their book “How to Eat Well and Stay Well the Mediterranean Way.” Below is a chronology of how a postwar research project turned into the most recommended diet on earth, and where the critique of it stands.
The Seven Countries Study, 1958
The origin point is Keys’ Seven Countries Study, launched in 1958. Keys had noticed in the early 1950s that the business executives he saw in Minnesota seemed to have higher cholesterol and more heart attacks than the post-war poor of Naples, where food was scarce and fat came mostly from olive oil rather than butter. Between 1958 and 1970 his team gathered diet and health data from roughly 12,700 middle-aged men in the United States, Finland, the Netherlands, Italy, Greece, Yugoslavia and Japan. The core finding, published through the 1970s and 1980s, was that cohorts eating less saturated fat, and more olive oil, legumes, fruit and vegetables, had strikingly lower rates of coronary heart disease. Crete, where the diet was closest to the archetype, had the lowest coronary mortality of all cohorts tracked.
The study has been criticised ever since for its methods: Keys selected countries rather than randomising them, and the famously low heart-disease figures from Crete were collected during Lent, when the observant Orthodox population was fasting from meat and dairy. That last point, raised repeatedly in the literature since, is the single most quoted caveat in the entire field.
The 1990s: the pyramid and the first definition
The diet had no formal public definition until 1993, when Oldways, the Harvard School of Public Health and the World Health Organization jointly introduced the Mediterranean Diet Pyramid at a conference in Cambridge, Massachusetts. The pyramid codified what had been a research observation into an eat-more, eat-less schematic: olive oil as the principal fat; abundant vegetables, fruit, legumes and whole grains; moderate fish, poultry, dairy and wine with meals; and meat and sweets as occasionals. In 1995 Willett and Trichopoulou set out the scientific basis in the American Journal of Clinical Nutrition, and Antonia Trichopoulou’s Mediterranean Diet Score, published in 1995 and revised in 2003, became the tool used to measure adherence in essentially every study since. If you read that a population was “highly adherent” to a Mediterranean diet in a paper, the odds are very good it was scored on Trichopoulou’s instrument.
The evidence peak: PREDIMED, 2013
The strongest single piece of evidence arrived in 2013: the PREDIMED trial from Spain, a randomised controlled study of over 7,400 people at high cardiovascular risk, which reported that a Mediterranean diet supplemented with extra-virgin olive oil or nuts reduced major cardiovascular events by roughly 30 percent compared with a low-fat control. It was a landmark precisely because almost everything before it had been observational, and it was reported worldwide.
Then came an unusually honest correction. In 2018, researchers including John Carlisle found randomisation irregularities at a number of PREDIMED’s study sites: some participants had been assigned to the same group as family members, and some sites assigned by clinic rather than individually. The New England Journal of Medicine retracted the 2013 paper in June 2018 and republished a reanalysed version in 2018 with the same headline conclusion, approximately a 30 percent reduction in cardiovascular events, but with wider confidence intervals and the irregular sites excluded. The episode is a case study in how a landmark trial can be methodologically flawed and directionally right at the same time.
UNESCO recognition, 2010 and 2013
Separately from the science, the diet acquired cultural standing. UNESCO inscribed the Mediterranean Diet on its Representative List of the Intangible Cultural Heritage of Humanity in 2010 (initially for Spain, Greece, Italy and Morocco) and widened the inscription in 2013 to include Cyprus, Croatia and Portugal. This is the citation most media pieces lean on, and it is worth noting it recognises a way of life, food, conviviality and seasonal eating, rather than endorsing any health claim.
The U.S. News era, 2018 onward
The diet has topped the U.S. News & World Report Best Diets ranking every year since 2018, judged by a panel of diet, diabetes and heart experts on criteria including nutritional completeness, safety and long-term sustainability. DASH and the flexitarian diet typically follow it. The ranking is editorial rather than scientific research, but it drives an enormous amount of public adoption, and it is the reason your doctor has heard of the diet even if your doctor has not read PREDIMED.
Where the critique stands
The serious criticisms are four. First, the Crete-during-Lent sampling problem described above: the founding observation may have been measured at the population’s most ascetic moment. Second, the diet is unfalsifiable as commonly described, because “eat mostly plants, olive oil and fish” describes a dozen national cuisines, and any of them can be credited when outcomes are good. Third, PREDIMED’s retraction, even with the republished reanalysis, weakened the claim to have randomised-trial evidence. Fourth, the modern “Mediterranean diet” sold in supermarkets bears little resemblance to the 1960s Cretan peasant diet it was derived from, which was low in total calories and meat by necessity, not by choice. As Trichopoulou herself has noted in later reviews, the original diet was a diet of poverty; the contemporary version is a diet of aspiration with the same ingredient list.
None of these critiques overturn the observation that the pattern is associated with good cardiovascular outcomes. They do mean the eight-year reign at the top of the rankings rests on observational data, one troubled but republished trial, and a cultural inheritance that was never designed as a health intervention.