Not just a monounsaturated fat anymore

I wrote yesterday about the effect of polyphenols in fruit juices on the risk of Alzheimer's disease. Polyphenols aren't just in fruit juices, however. Another excellent source of polyphenols is virgin olive oils, the oils from the first pressing of olives. The heart-healthy effects of the olive oil in the Mediterranean Diet has often been attributed to its being a monounsaturated fat, but researchers in Europe theorized that they might be the polyphenols in the olive oil (Ann Intern Med 2006; 145(5): 333-341).

To test this, Dr. Maria-Isabel Covas and her colleagues obtained virgin olive oil (high in polyphenols) and refined olive oil (low in polyphenols) from the same source, and created a third type, a medium-polyphenol olive oil, by mixing the high- and low-polyphenol olive oils together. Meanwhile, 200 male volunteers were recruited through research centers in five European countries. The volunteers were all healthy, did not smoke, had blood cholesterol levels within normal ranges, and were not taking blood-thinning medications or supplements.

In a study type known as a crossover study, each volunteer consumed 25ml (about one and a half tablespoons) of one of the types of olive oil (low, medium, or high polyphenol) each day for three weeks, in place of a similar amount of margarine or other fat. For two weeks they then ate their normal diet, then repeated the cycle twice more with the other two types of olive oil. The subjects' cholesterol levels were tested before and after each olive oil period. Neither the participants nor the investigators knew which olive oil they were consuming until after the study was completed.

All the volunteers' cholesterol levels were improved regardless of which type of olive oil they were taking: they saw increased HDL cholesterol levels, a decreased ratio of total cholesterol to HDL cholesterol, and reduced levels of triglycerides. Yet the researchers found that the medium- and high-polyphenol olive oils also decreased the ratio of LDL cholesterol (the bad stuff) to HDL cholesterol (the good stuff), and reduced the level of oxidized LDL (the really bad stuff) circulating in the bloodstream. These effects were more pronounced the higher the level of polyphenols in the olive oil.

What this means for you:

Although this is a short-term study, the positive effects of the Mediterranean Diet in general are well-established. Just choose virgin olive oil over the more refined olive oils - virgin olive oil isn't just better for you, it tastes better, too. Read my Dr. Tim Says article on the Mediterranean Diet.

First posted: September 6, 2006