Because the Mediterranean diet has shown such tremendous protection against cancer and heart disease, researchers felt that it might be doing this at a genetic level. To test this hypothesis, they gave one of the key components of a Mediterranean diet—olive oil—to men and women with metabolic syndrome, which is a precursor for heart disease and diabetes and is characterized by abdominal obesity.

The researchers, who published the results of their study in the July 2012 edition of the Journal of Nutrition, divided the study participants into three groups. For eight weeks, one group ate a diet with 19 percent of its calories from saturated fats such as butter. Another group got 20 percent of its calories from refined olive oil, which is a monounsaturated fat, and the third group ate a Mediterranean diet with 21 percent of its calories from extra virgin olive oil.

For each group of participants, researchers evaluated several parameters that involved the production of inflammatory compounds that play a key role in the development of atherosclerosis (hardening of the arteries).

The results indicated that eating olive oil rather than saturated fat decreased the expression of the genes that produce a number of inflammatory compounds. These results are quite significant because they shows that some of the underlying beneficial effects of olive oil and the Mediterranean diet against cancer and heart disease may be due to their direct effects on the expression of our DNA.

Why is this important? Our genes provide all of the information needed to produce the proteins and other molecules necessary to create our cells and tissues. However, the manner in which our DNA expresses its instructions to build these molecules is highly regulated by factors outside the genes. These factors, referred to as "epigenetic factors,"  are in turn highly influenced by diet and environmental factors.

Olive oil is thought to protect against disease not only because of its monounsaturated fat, but also because it contains several important antioxidants. Along with using olive oil as the main source of fat, key components of the Mediterranean diet include:
• An abundance of plant food (fruit, vegetables, bread, past, potatoes, beans, nuts and seeds)
• Minimally processed foods, with a focus on seasonal and locally grown ingredients
• Consumption of sweets containing sugar or honey only a few times a week  at the most
• Daily consumption of low to moderate amounts of dairy products (principally cheese and yogurt)
• Regular consumption of fish
• Low to moderate consumption of poultry and eggs (1 to 4 times weekly), or not at all
• Low consumption of red meat
• Mild to moderate consumption of wine, normally with meals