Although it was first publicized in 1945 by the American doctor Ancel Keys stationed in Salerno, Italy, the Mediterranean diet failed to gain widespread recognition until the 1990s. It is based on what from the point of view of mainstream nutrition is considered a paradox: that although the people living in Mediterranean countries tend to consume relatively high amounts of fat, they have far lower rates of cardiovascular disease than in countries like the United States, where similar levels of fat consumption are found. A parallel phenomenon is known as the French Paradox.
One of the main explanations is thought to be the large amount of olive oil used in the Mediterranean diet. Unlike the high amount of animal fats typical to the American diet, olive oil lowers cholesterol levels in the blood. It is also known to lower blood sugar levels and blood pressure. Research indicates olive oil prevents peptic ulcers and is effective in treatment of peptic ulcer disease, and may be a factor in preventing cancer. In addition, the consumption of red wine is considered a possible factor, as it contains flavonoids with powerful antioxidant properties.
The principal aspects of this diet include high olive oil consumption, high consumption of legumes, high consumption of unrefined cereals, high consumption of fruits, high consumption of vegetables, moderate consumption of dairy products (mostly as cheese and yogurt), moderate to high consumption of fish, low consumption of meat and meat products, and moderate wine consumption.
Michael Pollan suggests the explanation is not any particular nutrient, but the combination of nutrients found in unprocessed food.
Dietary factors may be only part of the reason for the health benefits enjoyed by these cultures. Genetics, lifestyle (notably heavy physical labor), and environment may also be involved.
Although green vegetables, a good source of calcium and iron, as well as goat cheese, a good source of calcium, are common in the Mediterranean diet, concerns remain whether the diet provides adequate amounts of all nutrients, particularly calcium and iron.
This diet is not typical of all Mediterranean cuisine. In Northern Italy, for instance, lard and butter are commonly used in cooking, and olive oil is reserved for dressing salads and cooked vegetables. In North Africa wine is traditionally avoided by Muslims. In both North Africa and the Levant, along with olive oil, sheep's tail fat and rendered butter (samna) are traditional staple fats.
The Lyon Diet Heart Study set out to mimic the Cretan diet, but adopted a pragmatic approach. Realizing that some of the people in the study (all of whom had survived a first heart attack) would be reluctant to move from butter to olive oil, they used a margarine based on rapeseed (canola) oil. The dietary change also included 20% increases in vitamin C rich fruit and bread and decreases in processed and red meat. On this diet, mortality from all causes was reduced by 70%. This study was so successful that the ethics committee decided to stop the study prematurely so that the results of the study could be made available to the public immediately.
According to a study published in the British Medical Journal (May 29, 2008), the traditional Mediterranean diet provides substantial protection against type 2 diabetes. The study involved over 13 000 graduates from the University of Navarra in Spain with no history of diabetes, who were recruited between December 1999 and November 2007, and whose dietary habits and health were subsequently tracked. Participants initially completed a 136-item food frequency questionnaire designed to measure the entire diet. The questionnaire also included questions on the use of fats and oils, cooking methods and dietary supplements. Every two years participants were sent follow-up questionnaires on diet, lifestyle, risk factors, and medical conditions. New cases of diabetes were confirmed through medical reports. During the follow-up period (median 4.4 years) the researchers from the University of Navarra found that participants who stuck closely to the diet had a lower risk of diabetes. A high adherence to the diet was associated with an 83% relative reduction in the risk of developing diabetes.
A study published in The New England Journal of Medicine (July 17, 2008) examined the effects of the three diets: Low-carb, Low-fat, and Mediterranean. The study involved 322 participants and lasted for the a duration of 2 years. The low-carb and Mediterranean diet resulted in the highest weight-loss, 12 lbs and 10 lbs, respectively. The low-fat diet resulted in a loss of 7 lbs. One caveat of the study is that 86% of the study participants were men. The low-carb and Mediterranean diets produced similar amounts of weight loss in the overall study results and in the men. In the remaining participants who were women, the Mediterranean diet produced 3.8 kg (8.4 lbs) more weight loss on average than the low-carb diet.