Bottomline:  The classic Mediterranean diet is low in omega-6 fats.

Summary Researchers analyzed existing Mediterranean diet studies, which involved more than 1.5 million healthy people.  While there was not a standard definition of what constitutes a Mediterranean diet--this overall pattern of eating was  significantly associated with a reduced risk of death from all causes and a reduced risk of death from heart disease and cancer.  The incidence of cancer, Parkinson’s disease and Alzheimer’s disease was also significantly reduced.
Study Quote: "A diet rich in fruits, vegetables, legumes, and cereals, with olive oil as the only source of fat, moderate consumption of red wine especially during meals, and low consumption of red meat has been shown to be beneficial..."

Commentary:One hallmark of the Mediterranean diet is that it is low in omega-6 fat, a fact that is often overlooked, (dare I say neglected) in spite of the studies indicating its health significance!  Among vegetable oils, olive oil is one of the lowest in omega-6 fat, providing 1.3 grams of linoleic acid (the plant source of omega-6 fat).  Olive oil is predominantly  oleic acid, an omega-9 fatty acid).

Examples:

• The Lyon Diet Heart Study-which popularized the health benefits of eating a Mediterranean diet was designed and implemented as a low dietary omega-6 fat of 7 grams/day; because the researchers determined that it was one of the key features of following a Mediterranean diet ( de Lorgeril et al.)  That  study was published with an accompanying editorial by A. Leaf, who highlighted the importance of the low dietary omega-6 factor for heart health.
  

• The Greek Mediterranean diet, as exemplified by the diet of Crete, is associated with the longest life expectancy and lowest rate of cardiovascular disease. It is a low omega-6 fat. And this is the Mediterranean diet, which the Lyon Diet Heart was patterned.(Simopoulos AP )

• The Chianti Study–Researchers evaluated the population of two small towns in Tuscany, Italy for the effect of dietary fat and inflammation.  Notably, the people in this Mediterranean region eat a low omega-6 fat diet, with an average intake of 7 grams of polyunsaturated fats (PUFA) per day.(Ferrucci L et al.)  This diet was associated with lower levels of proinflammatory biomarkers (IL-6, IL-1ra, TNF, C-reactive protein) and higher levels of anti-inflammatory biomarkers (soluble IL-6r, IL-10, TGFß).
  

Considering that many westernized countries eat very high levels of omega-6 fats, (including eating fats that didn't exist 100 years ago, like cottonseed oil and margarine); it might be helpful to define what is not a Mediterranean diet (it is not high in omega-6 fats).  And yet, these are the very fats (polyunsaturated fats) that have been touted for years by the American Heart Association, because they are considered heart healthy.   Currently, the average American eats twice the maximum international recommendations of no more than 6.7 grams of omega-6 fat/day.

Link to Studies:
de Lorgeril M et al.
Mediterranean Diet, Traditional Risk Factors, and the Rate of Cardiovascular Complications After Myocardial Infarction : Final Report of the Lyon Diet Heart Study Circulation1999;99:779-785 (Free full text)

Ferrucci L et al. Relationship of Plasma Polyunsaturated Fatty Acids to Circulating Inflammatory Markers J. Clin. Endocrinol. Metab. 2006 91: 439-446; 2005-1303 (Free full text)

Leaf A.
Dietary Prevention of Coronary Heart Disease : The Lyon Diet Heart Study Circulation 1999;99:733-735 (Free full text)

Simopoulos AP.
What Is So Special about the Diet of Greece? The Scientific Evidence World Rev Nutr Diet. Basel, Karger, 2005, 95:80-92 .(Abstract w/free preview)

Sofi F et al.
Adherence to Mediterranean diet and health status: meta-analysis BMJ 2008 337: a1344-a1344 (Free full text)