Olive oil comes from the fruit of olive trees and has been consumed for thousands of years. It's known today for its many health benefits and culinary usefulness, with extra virgin olive oil being the healthiest.

Extra virgin olive oil is made by squeezing the juice directly out of crushed olives, and is the only cooking oil made without chemicals or industrial assistance. Since the oil is absent any additives, quality is influenced by factors such as where they're grown and a given producer's methods, according to oliveoiltimes.com.

The highest of the five grades of olive oil classifications, extra virgin is also the most expensive, but with that comes more healthful properties than ordinary olive oils.

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"The highest grade is extra-virgin olive oil, and it's the only one I recommend," writes obesity researcher and neurobiologist Stephan Guyenet on his Whole Health Science blog. "It's the only grade that's not heated or chemically refined in any way."

The monounsaturated fat in extra virgin olive oil may lower total cholesterol and low-density lipoprotein, or LDL (the "bad" cholesterol) in blood, according to the Harvard School of Public Health. Also, in a December 2014 study by the University of Florence, researchers determined that the levels of phenol in extra virgin olive oil help inhibit the growth of colon cancer cells.

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Extra virgin olive oil also contains helpful vitamin E and K, as well as natural antioxidants which can boost the immune system and reduce the risk of obesity and Type 2 diabetes.

In a post for authoritynutrition.com, founder Kris Gunnars details reasons why extra virgin olive oil is the healthiest oil, and why it's the only type he recommends. Among his reasons, Gunnars lists the oil's anti-inflammatory substances, protection against cardiovascular disease, and ingredients believed to have a hand in fighting cancer and Alzheimer's disease.

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