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The Mediterranean diet is a modern nutritional recommendation inspired by the traditional dietary patterns of Greece, southern Italy, and Spain The principal aspects of this diet include proportionally high consumption of olive oil, legumes, unrefined cereals, fruits, and vegetables, moderate to high consumption of fish, moderate consumption of dairy products (mostly as cheese and yogurt), moderate wine consumption, and low consumption of meat and meat products.
Despite its name, 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 both North Africa and the Middle East, sheep's tail fat and rendered butter (samna) are the traditional staple fats, with some exceptions.
The most commonly understood version of the Mediterranean diet was presented, amongst others, by Dr Walter Willett of Harvard University's School of Public Health from the mid-1990s on. Based on "food patterns typical of Crete, much of the rest of Greece, and southern Italy in the early 1960s", this diet, in addition to "regular physical activity," emphasizes "abundant plant foods, fresh fruit as the typical daily dessert, olive oil as the principal source of fat, dairy products (principally cheese and yogurt), and fish and poultry consumed in low to moderate amounts, zero to four eggs consumed weekly, red meat consumed in low amounts, and wine consumed in low to moderate amounts". Total fat in this diet is 25% to 35% of calories, with saturated fat at 8% or less of calories.
Olive oil is particularly characteristic of the Mediterranean diet. It contains a very high level of monounsaturated fats, most notably oleic acid, which epidemiological studies suggest may be linked to a reduction in coronary heart disease risk. There is also evidence that the antioxidants in olive oil improve cholesterol regulation and LDL cholesterol reduction, and that it has other anti-inflammatory and anti-hypertensive effects.
Although it was first publicized in 1945 by the American doctor Ancel Keys stationed in Pioppi, Italy, the Mediterranean diet failed to gain widespread recognition until the 1990s. Objective data showing that Mediterranean diet is healthy, first originated from the Seven Countries Study.
Mediterranean diet 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.
A diet rich in salads was promoted in England during the early Renaissance period by Giacomo Castelvetro in A Brief Account of the Fruits, Herbs, and Vegetables of Italy. He attempted, without success, to convince the English to eat more fruits and vegetables.
A number of diets have received attention, but the strongest evidence for a beneficial health effect and decreased mortality after switching to a largely plant based diet comes from studies of Mediterranean diet, e.g. from the NIH-AARP Diet and Health Study.
The Mediterranean diet often is cited as beneficial for being low in saturated fat and high in monounsaturated fat and dietary fiber. One of the main explanations is thought to be the health effects of olive oil included in the Mediterranean diet.
The Mediterranean diet is high in salt content. Foods such as olives, salt-cured cheeses, anchovies, capers, and salted fish roe all contain high levels of salt.
Dietary factors are only part of the reason for the health benefits enjoyed by certain Mediterranean cultures. A healthy lifestyle (notably a physically active lifestyle or labour) is also beneficial. Environment may also be involved. However, on the population level, i.e. for the population of a whole country or a region, the influence of genetics is rather minimal, because it was shown that the slowly changing habits of Mediterranean populations, from a healthy active lifestyle and Mediterranean diet to a not so healthy, less physically active lifestyle and a diet influenced by the Western pattern diet, significantly increases risk of heart disease. There is an inverse association between adherence to the Mediterranean diet and the incidence of fatal and non fatal heart disease in initially healthy middle aged adults in the Mediterranean region.
A 2011 systematic review found that a Mediterranean diet appeared to be more effective than a low-fat diet in bringing about long-term changes to cardiovascular risk factors, such as lowering cholesterol level and blood pressure. 
A 10-year study found that adherence to a Mediterranean diet and healthful lifestyle was associated with more than a 50% lowering of early death rates. A 5-year study of 7,447 people reported that the Mediterranean diet reduced the risk of heart disease in people at high risk by "about 30 percent" when compared with individuals on just a low fat diet.
The putative benefits of the Mediterranean diet for cardiovascular health are primarily correlative in nature; while they reflect a very real disparity in the geographic incidence of heart disease, identifying the causal determinant of this disparity has proven difficult. The most popular dietary candidate, olive oil, has been undermined by a body of experimental evidence that diets enriched in monounsaturated fats such as olive oil are not atheroprotective when compared to diets enriched in either polyunsaturated or even saturated fats. A recently emerging alternative hypothesis to the Mediterranean diet is that differential exposure to solar ultraviolet radiation accounts for the disparity in cardiovascular health between residents of Mediterranean and more northerly countries. The proposed mechanism is solar UVB-induced synthesis of Vitamin D in the oils of the skin, which has been observed to reduce the incidence of coronary heart disease, and which rapidly diminishes with increasing latitude. Interestingly, residents of the Mediterranean are also observed to have very low rates of skin cancer (which is widely believed to be caused by over-exposure to solar UV radiation); incidence of melanomas in the Mediterranean countries is lower than in Northern Europe and significantly lower than in other hot countries such as Australia and New Zealand. Its been hypothesized that some components of the Mediterranean diet may provide protection against skin cancer.
A study published in the Archives of General Psychiatry shows that people who followed the Mediterranean diet were less likely to develop depression.
The Seven Countries Study found that Cretan men had exceptionally low death rates from heart disease, despite moderate to high intake of fat. The Cretan diet is similar to other traditional Mediterranean diets, consisting mostly of olive oil, bread, abundant fruit and vegetables, fish, and a moderate amount of dairy foods and wine.
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 it prematurely so that the results could be made public immediately.
According to a 2008 study published in the British Medical Journal, 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 2008 study published in The New England Journal of Medicine examined the effects of three diets: low-carb, low-fat, and Mediterranean. The study involved 322 participants and lasted for two years. The low-carb and Mediterranean diet resulted in the greatest 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. However, the low-carb diet produced more favorable changes in blood lipids.
A meta-analysis published in the British Medical Journal in 2008 showed that following strictly the Mediterranean diet reduced the risk of dying from cancer and cardiovascular disease as well as the risk of developing Parkinson's and Alzheimer's disease. The results report 9%, 9%, and 6% reduction in overall, cardiovascular, and cancer mortality respectively. Additionally a 13% reduction in incidence of Parkinson's and Alzheimer's diseases is to be expected provided strict adherence to the diet is observed. As well, a 2007 study found that adherence to the Mediterranean diet (MeDi) may affect not only risk for Alzheimer disease (AD) but also subsequent disease course: Higher adherence to the MeDi is associated with lower mortality in AD. The gradual reduction in mortality risk for higher MeDi adherence tertiles suggests a possible dose-response effect.
A study published in the British Medical Journal in 2009 showed some components of the Mediterranean diet, such as high vegetable consumption and low meat and meat product consumption, are more significantly associated with low risk of mortality than other components, such as cereal consumption and fish consumption. As part of the European Prospective Investigation into Cancer and Nutrition study, researchers followed more than 23,000 Greek men and women for 8.5 years to see how various aspects of a Mediterranean diet affect mortality. Moderate alcohol consumption, high fruit and nut consumption, and high legume consumption were also associated with lower risk of mortality. Mediterranean Diet, articulated into extensive lifestyles interventions in a clinical follow-up study, improves renal artery circulation, decreasing renal resistive index, even without significant modifications of Insulin Resistance. This is a beneficial effect and modifies the pathophysiology of essential hypertension. Another study reported in February 2010 found that the diet may help keep the brain healthy by reducing the frequency of mini-strokes that can contribute to mental decline. Mediterranean Diet is becoming a comprehensive popular and successful translational paradigm for the promotion of healthier lifestyles.
A 2011 meta-analysis published in the Journal of the American College of Cardiology analyzed the results of 50 studies (35 clinical trials, 2 prospective and 13 cross-sectional) covering about 535,000 people to examine the effect of a Mediterranean diet on metabolic syndrome. The researchers reported that a Mediterranean diet is associated with lower blood pressure, blood sugar, and triglycerides.
A 2012 follow-up study in Israel, published in the New England Journal of Medicine, found that even people who regain some weight after going on a Mediterranean diet can derive lasting benefits from it.
A meta-analysis published in the American Journal of Clinical Nutrition in 2013 compared Mediterranean, vegan, vegetarian, low-glycemic index, low-carbohydrate, high-fiber, and high-protein diets with control diets. The research concluded that Mediterranean, low-carbohydrate, low-glycemic index, and high-protein diets are effective in improving markers of risk for cardiovascular disease and diabetes.
A recent randomized Spanish trial of diet pattern published in the New England Journal of Medicine in 2013 followed almost 7,500 individuals over around 5 years found that individuals on a Mediterranean diet supplemented with mixed nuts and olive oil had a 30 percent reduction in risk of having a major cardiovascular event and a 49 percent decrease in stroke risk. Subjects followed one of three different diets. They included either a low fat diet, a Mediterranean diet with 50 ml of extra virgin olive oil daily or a Mediterranean diet with 30 grams of mixed nuts. The nuts were primarily walnuts which have a high amount of omega-3 fatty acids. 
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