On Olive Oil

Q: What do you think of new research showing that olive oil causes blood vessels to constrict by 34 percent, injuring their lining and contributing to heart disease, and recommendations to stay away from olive oil because it impairs blood vessel function just like a Big Mac with fries or cheesecake?

A: The notion that olive oil could be as bad for you as Big Macs, fries, or cheesecake came from study results presented (but not yet published in a medical journal) more than a year ago at a meeting of the American College of Cardiology by heart specialist Robert Vogel, MD, of the University of Maryland.

Dr. Vogel reported on a small study in which he tested the effects of three different meals on a group of 10 volunteers who had normal cholesterol levels. Each meal contained 50 grams of fat. One meal was canola oil and bread, another was olive oil and bread, and the third was a piece of salmon. Before and three hours after each meal, Dr. Vogel and his fellow researchers measured constriction of the volunteers’ arteries, a change that Dr. Vogel says can damage the inner lining of blood vessels. The salmon meal didn’t have much effect, and the canola oil meal lowered blood flow by 11 percent. However, the olive oil and bread meal reduced blood flow by 34 percent, the same change Dr. Vogel had seen in earlier studies when volunteers ate a Big Mac and fries.

Does this mean that we all should disregard the vast body of reassuring epidemiological evidence that olive oil is good for us and that rates of heart disease are lowest in countries where olive oil is a dietary staple? I posed this question to Walter Willett, MD, of the Harvard School of Public Health, author of Eat, Drink, and Be Healthy: The Harvard Medical School Guide to Healthy Eating (Simon & Schuster, 2001) and one of the country’s most distinguished nutrition researchers. Here’s what Dr. Willett said:

“Studies that look at short-term effects of one variable at a time should never be used in making decisions about diet. The effect of olive oil, or any other food, on heart disease or overall health is mediated by many different pathways, including influences on blood cholesterol fractions, blood clot formation, heart rhythm, oxidative stress, and numerous other processes. Looking at just one or two of these variables in isolation can be completely misleading.”

Dr. Willett continues to believe in the safety of olive oil consumption, even in large amounts. I share this opinion, and my dietary recommendations to prevent heart disease encourage the use of extra-virgin olive oil along with a high intake of omega-3 oils and other foods rich in antioxidants. Based on the evidence we have today, there is no reason I know of to avoid olive oil.

Andrew Weil, M.D.

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