Phenolic compounds in olive oil, which have antioxidant, anti-inflammatory and anti-clotting properties, may explain cardiovascular health benefits associated with the so-called Mediterranean Diet, according to a new study in the Nov. 15, 2005, issue of the Journal of the American College of Cardiology.
"It could be that the beneficial effect of the Mediterranean diet on cardiovascular disease and arteriosclerosis depends on the synergistic effects of the different nutrients that constitute complete foods and, as an example, virgin olive oil is more than fat because it is a real juice with other healthy micronutrients," said Francisco Pérez Jiménez, M.D., Ph.D., from the Reina Sofia University Hospital in Córdoba, Spain.
The researchers, including lead author Juan Ruano, M.D., Ph.D., fed breakfasts including olive oil (that was either high or low in phenolic content) to 21 study participants (5 men, 16 women) who had high cholesterol levels, but were otherwise apparently healthy. The functioning of the endothelium (the inner lining) of small blood vessels of the fingers (instead of "in the arms") of participants and the concentrations of certain components in blood serum, including nitric oxide, improved after the polyphenol-rich breakfast.
"This is the first study that shows a direct benefit of an olive oil with high content in phenolic compounds on endothelial function in vivo," Dr. Pérez Jiménez said.
After fasting overnight, the participants reported to the hospital, where they ate a breakfast of 60 grams of white bread with 40 milliliters of virgin olive oil, a relatively high-fat meal. The meals also included vitamin A supplementation. Over the next four hours, blood samples were taken and the researchers used Doppler laser to measure endothelial responses to sudden changes in blood flow, which were produced by inflating and then deflating a blood pressure cuff. The response is known as ischemic reactive hyperemia. Poor responsiveness to this sort of blood flow test is considered an early warning sign of cardiovascular disease. Previous studies have linked high-fat meals to poor endothelial function lasting for several hours after eating.
In order to focus on the role of phenolic compounds, the researchers put each participant through the process twice in a randomized order, once using olive oil naturally high in phenolic compounds (400 parts per million) and once with the same brand of olive oil that had been processed to remove most of the phenolic compounds (80 parts per million remaining).
"We think, looking at our results, that the reduction in oxidative stress and the increase in the nitric oxide bioavailability are behind the observed improvement in ischemic reactive hyperemia," Dr. Pérez Jiménez said.
Dr. Pérez Jiménez said that olive oil may be superior to seed oils because it is a natural juice, pressed from the olives, so it does not go through the type of processing needed to extract oil from seeds, such as sunflowers, soybeans and rapeseeds. Nevertheless, he said further studies should be done to investigate whether phenolic compounds in olive oil can be linked to improved health outcomes.