NEW YORK (Reuters Health) - Eating foods prepared with olive oils that are rich in phenols, substances though to have beneficial effects on the heart, may help ward off harmful blood clots in people with high cholesterol, Spanish researchers report.

"Our findings provide new evidence of the healthy effects of virgin olive oil," Dr. Francisco Perez-Jimenez of Reina Sofia University Hospital in Cordoba and colleagues conclude.

In the early stages of atherosclerosis, the balance between clot-promoting and clot-dissolving factors in the blood vessels shifts in favor of clot formation and having high levels of fat in the blood can worsen this imbalance, Perez-Jimenez and his team explain the August issue of the American Journal of Clinical Nutrition.

Olive oil contains phenols, which have been shown to fight clotting in lab tests, but few studies of their effects have been performed in humans, the researchers note.

To investigate, the researchers had 21 people with high cholesterol eat two different breakfasts. For one week, they consumed either white bread with virgin olive oil containing 400 parts per million phenols, or white bread with olive oil from which much of the phenols had been extracted, leaving it with 80 parts per million. Study participants were then switched to the opposite meal.

Two hours after the high-phenol meal, study participants' concentrations of factor VII antigen, which promotes blood clotting, were lower compared with the low-phenol group. The high-phenol group also experienced a greater drop in the activity of another clot promoter, plasminogen activator inhibitor-1.

The researchers suggest that previous studies that have yielded inconsistent results regarding olive oil's effect on the blood may have been due to variations in phenol content.

"Although this study deals with the microcomponents of virgin olive oil, we should still think in terms of evaluating the biological properties of complete foods," the researches add.

With this in mind, they conclude that the current study supports the heart health benefits of virgin olive oil.