Reporting in the Annals of Internal Medicine, European researchers say virgin olive oil may be particularly effective at lowering heart disease risk because of its high level of antioxidant plant compounds.

In a study of 200 healthy men, the researchers found that virgin olive oil - rich in antioxidants called polyphenols - showed stronger heart-health effects than the more extensively processed "non-virgin" variety.

The findings suggest that virgin olive oil has more going for it than its supply of heart-healthy monounsaturated fat, according to the study authors. Polyphenols, they say, may account for some of the health benefits that have been attributed to the oil.

In fact, virgin olive oil is the only vegetable oil that's rich in polyphenols, Dr. Maria-Isabel Covas, the study's lead researcher, told Reuters Health.

"All vegetable oils other than virgin olive oil are submitted to a (refining) process in which polyphenols are practically lost," explained Covas, a researcher at the Municipal Institute for Medical Research in Barcelona, Spain.

Even "ordinary" olive oil has a lower polyphenol content, she noted, because it's a mixture of virgin olive oil and a more-processed form of the oil.

For their study, Covas and her colleagues had 200 young and middle-aged men use each of three olive oils for three weeks apiece. One oil was a virgin olive oil high in polyphenols; the other two were more heavily processed varieties with moderate to low polyphenol levels.

The men used the oils in place of other dietary fats.

At the end of the study, the researchers found that the men's levels of "good" HDL cholesterol were highest after their three weeks on virgin olive oil. They also showed a greater decline in markers of so-called oxidative stress -- a process that helps deposit particles of "bad" LDL cholesterol on the artery walls and can lead to a hardening and narrowing of the vessels supplying the heart.

Monounsaturated fat is well known to be a healthier alternative to the saturated fat found in animal products like butter, Covas noted. That fact, along with the benefits of polyphenols, she said, make olive oil "a good source of fat."

But she stopped short of recommending virgin olive oil as a replacement for other vegetable oils, saying large clinical trials are needed to see whether there's a health advantage.

SOURCE: Annals of Internal Medicine, September 5, 2006.