Olive oil is known to lower the risk of many health problems. It contains the monounsaturated fats that can lower heart disease, keep blood sugar in check, and potentially help with blood clotting problems. Mayo Clinic doctors report that while it is important to watch the calories added by olive oil, the health benefits of the food are well established.

According to the U.S. Department of Agriculture (USDA), there are four basic types of olive oil in addition to "olive pomace oil" – which has three subtypes. The basic olive oil types are extra virgin, virgin, and refined. Olive pomace oil includes refined olive-pomace oil and crude olive pomace oil.

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The type of olive oil makes a big difference in health. According to Authority Nutrition, the healthiest types of olive oils are those that are naturally extracted — olives pressed until they release oil. Many qualities or grades are based on the way the oils taste and smell.

Extra virgin olive oil is considered by many experts to be the healthiest type of olive oil because it has been extracted naturally and has not been mixed with other oils.

The International Olive Council is trying to help consumers with a 2015 resolution by member countries to standardize the taste and other qualities of olive oil grades.

The United States Department of Agriculture grades olive oil based on criteria that may mean virgin olive oil is a bit healthier than the extra virgin variety. While oils labeled "U.S. Virgin Olive Oil" has a lower quality of flavor and odor than its "U.S. Extra Virgin Olive Oil" cousin, the virgin type is allowed to have up to 2.0 grams of oleic acid (free fatty acid) per 100 grams. That is significantly higher than the extra virgin, which is only allowed 0.08 grams per 100 grams.

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Bottles simply labeled "U.S. olive oil" have been refined and are usually a blend with virgin olive oils. They are allowed 1.0 gram of oleic acid per 100 grams of product. The "U.S. Refined Olive Oil" is only allowed 0.3 grams per 100 grams.

The International Olive Council offers a third designation of virgin olive oils - ordinary virgin olive oil, which is allowed a oleic acid content of up to 3.3 grams per 100 grams. However, this designation is not recognized by the United States and cannot be sold in all countries.

Oleic acid is the monounsaturated fatty acid most experts believe responsible for most of the health benefits of olive oil.

The American Journal of Clinical Nutrition points out that the extra virgin olive oil is produced by a more natural pressing technique used to extract oil. The journal also points to several other factors in olive oil, besides oleic acid, that can have health benefits.

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