Say No to Olive Oil? (cont.)

But their effect on blood vessels was very different. Before and again three hours after each meal, Vogel's team measured constriction of the volunteers' arteries. Sharp constriction can injure the inner lining of blood vessels, according to Vogel.

The arteries didn't constrict much after the salmon meal. After the meal containing canola oil, they constricted slightly, reducing blood flow by 11%. After the olive oil and bread combination, however, blood flow plummeted 34% -- exactly the effect that Vogel had seen in previous research after volunteers ate a Big Mac with fries.

The Hidden Culprit

Vogel believes the culprits in olive oil are the omega-9 fatty acids that make up most of the oil. These fatty acids seem to cause blood vessels to constrict. Omega-3 fatty acids, in contrast -- the same kind found in fish oil, and the ones added to canola oil -- don't appear to have this effect. What's that got to do with heart disease? "When blood vessels constrict, their lining, called the endothelium, may be injured," says Vogel. "Repeated injuries can add up to a higher risk of coronary heart disease." What's more, in people with diabetes, which typically causes damage to blood vessel linings, the effect of olive oil could worsen an already dangerous condition, Vogel says.

Worrisome? Maybe. But don't toss out that high-priced bottle of extra-virgin oil just yet. Dozens of other investigations, after all, have found important health benefits associated with olive oil. And though this latest finding is provocative, it's still just one study -- and a very small one at that.

"We're talking about an isolated biological effect, the constriction of blood vessels. But as yet there's no solid evidence that this has any direct meaning as far as heart disease goes," says Frank Sacks, MD, a cardiologist and researcher at Harvard Medical School. "It certainly hasn't been established as a risk factor, like elevated cholesterol or high blood pressure."

Oils to Lower Blood Pressure

And there is good evidence that replacing saturated fats like butter with olive oil -- or any other unsaturated oil, such as peanut, safflower, sunflower, or canola -- can improve those risk factors and lower the danger of heart disease. In some studies, in fact, olive oil seems to have the edge over other unsaturated vegetable oils.

Take one in the March 27th issue of the Archives of Internal Medicine, for instance. Italian researchers showed that eating olive oil can lower high blood pressure -- in some cases far enough that certain patients can throw away their medicine. The scientists compared olive oil to sunflower oil in a group of 23 patients. After six months, patients eating olive oil had lowered their blood pressure so much that they could cut their daily dose of high blood pressure medication by 48%. Eight were able to stop their medication entirely. Sunflower oil, however, showed no effect on patients' blood pressure.

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