How to get all the benefits of olive oil

You feel good about using olive oil, right? You know it's good for you, tasty and easy to use. Still, to get the most benefits -- and the best bang for your buck -- there's more you should know.

"The health benefits of olive oil are 99 percent related to the presence of the phenolic compounds, not the oil itself," says Nasir Malik, research plant physiologist at the U.S. Agriculture Department's Agricultural Research Service.

Malik is referring to the polyphenols in olive oil, nutrients also found in wine, tea, cocoa and many fruits and vegetables that have been discovered over the past decade to be the substances responsible for the bulk of olive oil's health benefits, without which "you might as well use canola oil," Malik says.

And when tested, polyphenols were surprisingly low in most commercially available olive oils, according to a recently published study conducted by the Agricultural Research Service, co-authored by Malik.

They also don't live up to international or U.S. Agriculture Department quality standards, according to studies conducted by the University of California at Davis Olive Center.

The good stuff

Polyphenols decrease heart disease risk factors by lowering blood pressure and cholesterol, reducing blood clotting, and improving the health of artery linings.

Researchers have discovered genes that, when activated, either increase or reduce your chances for metabolic syndrome, the name for a group of risk factors that together increase the risk for heart disease, America's No. 1 killer. Fresh, high-polyphenol olive oil affects these genes in a positive way, reducing your risk for heart disease. But low-polyphenol olive oil does not have the same effects, according to a recent study.

Polyphenols also reduce cancer risk by lowering inflammation and cellular proliferation. They act as antioxidants, reducing oxidation and cell damage, which leads to many degenerative diseases. They even reduce microbial activity and infections.

These benefits explain, in part, why the Mediterranean diet, high in olive oil, has been linked with superior health. But there is an advantage even the poorest of the poor in Mediterranean countries have enjoyed since at least 4,000 B.C.: freshly harvested olive oil. That's because olives were growing on trees in their own back yards; it was plentiful and cheap. But its freshness had been taken for granted.

Waning quality

Studies show that as days, weeks and months go by after harvest, the polyphenol content and health benefits of the oil diminish.

"Think of olive oil as olive juice with a maximum two-year shelf life," says Selina Wang, research director at the UC Davis Olive Center.

Several factors are responsible for the polyphenol content of olive oil, according to the experts:

Harvesting method: Rougher treatment and exposure to the elements reduces phenols.

The age of the trees: Older trees contain significantly more.

Olive maturation: Green olives contain more polyphenols than ripe olives, though it's easier to extract more oil from riper olives.

Processing: The less processing the better. "Extra-virgin" olive oil, which is cold-pressed only once, has the highest polyphenol levels. Two presses ("virgin" olive oil), reduces polyphenol content further, and oil with three extractions contains only about half the value of virgin olive oil. Highly refined or "light" olive oils, which use heat or chemicals in the refining process, have significantly lower polyphenol levels.

Storage: Any exposure of the harvested olives or the oil to heat, light or air will reduce polyphenol content.

Luckily, you no longer have to travel to Italy for high-quality extra-virgin olive oil, as it is now being produced in the United States. It's more likely to be fresh -- and with a price you can afford. It's tricky knowing whether the olive oil you're buying is high-quality, fresh extra-virgin olive oil. In most U.S. stores, I have found olive oil with harvest dates on perhaps one out of 20 bottles. Some have "sell-by" dates, which are usually two years after harvest, though there are no standards for a sell-by date. Look for a harvest date within the past year.

Even if oil has a harvest date, you won't know whether it has been harvested and handled to maximize polyphenols.

The way I handle this is by going to a specialty Italian shop or somewhere that I know sells California or Texas olive oil. I save expensive olive oil for drizzling on salads and use canola oil for cooking, especially with high heat.

The more consumers demand harvest dates and proper handling, the more these products will become available.