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Say No to Olive Oil?

Questioning a good fat.

WebMD Feature

May 19, 2000 -- Could olive oil -- long considered the healthiest fat around -- be as bad for us as cheeseburgers or creamy desserts?

That's the jaw-dropping conclusion of University of Maryland heart specialist Robert Vogel, MD. At the March meeting of the American College of Cardiology, he stunned the nutrition world by warning that olive oil could be as dangerous to your heart and arteries as a Big Mac or a giant piece of cheesecake. "If you've been using olive oil because you think it's healthy," says Vogel, "it's time to think again."

Olive Oil? Bad for Your Heart?

Unfortunately, we've grown used to this kind of dietary flip-flop. Many Americans have begun to wonder if even the experts know what they're talking about. One day margarine is good for you, the next it's bad. One day vitamin E protects against heart disease, the next it offers no benefit at all. Now it's olive oil's turn.

Vogel tested the effects of three different meals on a group of 10 volunteers who had normal cholesterol levels. One meal consisted of canola oil and bread. Another was olive oil and bread. The third meal was a piece of salmon. All three meals contained 50 grams of fat.

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.

In another study by Danish researchers, olive oil proved better than canola oil at warding off blood clots after a fatty meal. This may help prevent heart attacks, according to the report published in the December 1999 American Journal of Clinical Nutrition.

The most compelling evidence in favor of olive oil, however, comes from dozens of large studies looking at the diet and health of thousands of people in southern Italy and in Greece. "Here, where olive oil was a staple part of the traditional diet, heart disease rates were among the lowest in the world," says Ancel Keys, who led the famous Seven Countries Study.