Study Increases Understanding of the Benefits of a Mediterranean Diet

People who consume a diet similar to a Mediterranean diet tend to have lower levels of oxidative stress, according to researchers at Emory University.

The study findings were presented March 14 at the American Heart Association's Conference on Cardiovascular Disease Epidemiology and Prevention.

Oxidative stress is an imbalance of antioxidants and prooxidants in the cells of the body. It is linked to greater production of reactive oxygen species, harmful oxygen-containing molecules that contribute to the thickening of blood vessels and the formation of lesions leading to heart attack and stroke.

"We've known about the protective effect of the Mediterranean diet, but this begins to show how antioxidants in the diet may be bringing about that effect," says study leader Viola Vaccarino, MD, PhD, professor of medicine (cardiology) at Emory University School of Medicine and professor of epidemiology at Emory's Rollins School of Public Health.

Dr. Vaccarino and her team studied the association between diet and oxidative stress in 297 middle-aged men from the Vietnam Era Twin Registry maintained by the U.S. Department of Veterans Affairs.

Studying twins allowed the scientists to separate out the influence of genetic factors and familial elements such as mother's pregnant age, socioeconomic status of parents and family culture on oxidative stress.

Jun Dai MD, a researcher in Emory University's cardiovascular epidemiology group explains, "Our work shows that the effects of diet are independent from genetics and familial factors.

"It means everybody can benefit from a healthy diet, whether you have genetic risk factors for cardiovascular disease or not," adds Dr. Dai, who presented the findings at the conference.

People who consume a Mediterranean diet eat large amounts of fruit, vegetables, whole grain breads, fish and poultry. Olive oil is their main source of fat. They eat low or moderate amounts of dairy products such as cheese and yogurt and low amounts of red meat.

Dr. Dai points out that the Emory study did not gauge the effects of participants' consumption of specific antioxidant-containing fruits or vegetables. The idea that antioxidants are responsible for the Mediterranean diet's protective effects needs to be tested further, she says.

Researchers measured oxidative stress by determining the levels of two forms of glutathione, a natural antioxidant the body uses to soak up reactive oxygen species, in the blood. As the body uses up the reduced form of glutathione to fight oxidative stress, the pool of oxidized glutathione increases.

A study participant's Mediterranean diet "score" can range from zero to nine, with a higher score meaning a greater adherence to the Mediterranean diet.

A one-point difference in diet score between twins was associated with a 10 percent higher ratio between reduced and oxidized glutathione, or 10 percent lower oxidative stress.

Researchers calculated a participant's score by giving one point each in seven categories for an above-average intake of something desirable: grains, vegetables, fruits, legumes, fish, monounsaturated fats and moderate wine consumption, and one point each for a below-average intake of meat and dairy products.

Dr. Vaccarino's team also has shown an association between following a Mediterranean diet and lower levels of IL-6 in the blood, a marker for inflammation. The results were published online in the journal Circulation in December 2007.
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