Olive oil can help to lower cholesterol and blood pressure, prevent clogged arteries and cancer, and may even protect against Alzheimer’s disease. But not all olive oils are created equal. If you’re looking for health benefits, this is what you need to know.

Although scientists have yet to understand every component of olive oil, a specific category of nutrients, known as phenols, seem to be partially responsible for the oil’s beneficial effects. Phenols act as antioxidants, reducing internal rusting in our bodies, so to speak.

Studies have shown that when people consume olive oils rich in phenols, the nutrients influence at least 98 different genes. In simple terms, high-phenol olive oil turns off bad genes and turns on good ones, and the net effects are less atherosclerosis and less chronic inflammation that leads to heart disease, diabetes, cancer and dementia.

‘Extra Virgin’ Benefits

Extra virgin olive oils are the only ones that contain significant amounts of phenols because these are made by pressing olives (technically, the procedure is called milling) without heat or chemicals. The processing of other types — “virgin,” “pure,” or simply “olive oil” — does involve chemicals and/or heat and destroys nutrients. However, levels of the beneficial components vary among extra virgin olive oils.

Phenol levels depend on the climate, the type of olives and when, during the harvesting season, they were picked. Early in the harvest, when olives are green, phenol levels are at their peak, and then decline with ripeness. Lab tests can measure levels of the nutrients but your taste buds will also give you a clue.

This is how extra virgin olive oils are usually described:

• Robust or pungent (bitter, to varying degrees, and may tickle the back of your throat): highest level of phenols
• Medium (possibly slightly bitter): medium range of phenols
• Mild or fruity (not bitter): lowest, but still beneficial, level of phenols

Freshness Is the Key

It might seem as though, for health benefits, you should always choose the most robust olive oil you can find, but that’s not a very realistic approach. We’re talking about food here, not medicine your mother practically forced you to take when you were a kid.

Olive oil is beneficial when you eat it on a regular basis in place of unhealthy fats, such as butter or other saturated or trans fats. You won’t eat an olive oil you don’t like.

Freshness is the most important quality. Unlike wine, even the highest quality oil will not improve with age; its nutrients and taste will degrade. These are the key things to look for:

• The label should clearly say “Extra virgin olive oil.”
• Choose a dark bottle, as light shortens shelf life.
• Avoid bottles that sit on the top shelf in a supermarket, as these are more exposed to store lighting.
• Look for an expiration or “best before” date. A harvest or milling date, found on premium oils, is even better. Olive oil is best consumed within a year to 18 months of harvesting and, at most, within two years.
• Start using your olive oil right away and keep the bottle in a cupboard, out of direct light, and away from the stove or other sources of heat, but not in the fridge. Use it up within two or three months.
• High quality oils may have a seal or certification from a government agency or an independent certifying body, such as the North American Olive Oil Association (www.naooacertified.org) or the California Olive Oil Council (www.cooc.com, for California olive oils).

Premium oils with certifications do cost more, for a reason. Their cultivation and production requires a lot of care and results in oils that are rich in nutrients and flavor. Testing includes lab analysis and, most often, a panel of trained tasters with palates sensitive enough to detect defects resulting from improper handling or storage.

Tasting Before Buying

In many specialty stores, you can taste a variety of olive oils. Competitions are another way to identify some premium products. Check out winners of the Los Angeles International Extra Virgin Olive Oil Competition here, and look for a local store to get a taste.

Opportunities to experience more flavors are expanding as olives start to be cultivated in more states. California has an established industry and there are festivals in olive-growing areas. Texas has struck the olive kind of oil and the Texas Olive Oil Council (www.texasoliveoilcouncil.org) organizes festivals. And olives are being cultivated in Oregon, Arizona, and Georgia.

Extra virgin olive oil is an extremely versatile and delicious food. Once you get to know one that pleases your palate, life will never be the same.