Is it Safe to Cook with Olive Oil?

This is an answer to the many people who ask about cooking and frying in olive oil.
Rehan Zaidi

Olive oil has always been a nutrition saint. Its health benefits have been touted for ages – high in antioxidants, anti-inflammatory, anti-cancer…the list goes on. (1, 2) Heck, even the USDA agrees the stuff is great for our health!

Yet there’s a popular myth circulating in the Paleo community that it’s unsafe to cook with olive oil; that it isn’t stable and oxidizes when heated, forming harmful by-products in the process. While this is true for other oils like canola and vegetable oil, I’m here to tell you that it’s okay to cook with olive oil. It has some unique qualities that make it stable under cooking conditions, and provided you’re buying high quality olive oil to begin with, you can sauté to your heart’s content.

Do you avoid cooking with olive oil? Here’s why you shouldn’t worry.

What is fat oxidation?

There are three types of fatty acids: saturated, monounsaturated, and polyunsaturated. What defines them is their structure; a saturated fat has zero double bonds (thus it is “saturated” with hydrogen), while a monounsaturated fatty acid has one double bond, and a polyunsaturated fatty acid has more than one. Check out the diagrams below and notice that the saturated fatty acid (left) has no double bonds, while monounsaturated fatty acid (center) and polyunsaturated fatty acid (right) have one and two, respectively. The double bonds are the “kinks” in the chain.

Double bonds are unstable when they come in contact with a number of elements, such as light, heat, and oxygen. While we call certain fats “saturated” or “monounsaturated,” the truth is that the fats we cook with are made up of many different types of fatty acids and we refer to them by their majority. For example, coconut oil (what we call a saturated fat) is made of 90% saturated fat. This differs from butter (another saturated fat), which has only 60% saturated fatty acids, the rest of it being monounsaturated and polyunsaturated fat. Soybean oil, on the other hand, is about 60% polyunsaturated fats. All of these differ from olive oil, which is made up of 70% oleic acid, a monounsaturated fat.

Because polyunsaturated fats have the most double bonds of all the fatty acids, they are more susceptible to oxidation. When polyunsaturated fatty acids oxidize they form unhealthy molecules called advanced lipid oxidation end products (ALEs). These ALEs cause an inflammatory reaction in the circulatory system, as well as the liver, kidney, lungs, and gut, and are thought to have negative impacts on human health. (3) This is why a Paleo diet excludes dietary fats with high percentages of polyunsaturated fats.

Why olive oil is less prone to oxidation

There are two reasons why olive oil outperforms other vegetable oils when it’s heated.  First, it contains polyphenols and tocopherols which act to protect the oil from oxidation. Second, it’s made up of mostly monounsaturated fat – remember, that’s the one with only one double bond, which makes it more stable in heat than fats with high amounts of polyunsaturated fats which have more double bonds. Between these two properties, olive oil can fry with the best of them.

It is thought that the phenolic compounds in olive oil – polyphenols and tocopherols – may influence olive oil’s stability in heat even more than its monounsaturated fat content. The phenolic compounds donate a radical hydrogen to alkylperoxyl radicals to form a stabilized radical. (4) For the chemistry buffs out there, this reaction works like this: ROO• + AH → ROOH + A•

One study fried olive oil varieties to see how they stood up to high heat, and only after 24-27 hours of frying (depending on the type) were they considered to be harmful. Vegetable oil, on the other hand, was only able to go for 15 hours. Despite lower amounts of vitamin E, olive oil still ended up less oxidized than the vegetable oil. The researchers also found that the polyphenol content of olive oil predicted its susceptibility to oxidation; varieties with more polyphenols were less prone to oxidation while those with less became more oxidized. (5)

Other researchers heated extra virgin olive oil to 350°F for 36 hours (yes, you read that correctly. 36 hours!) and found that while there was some degradation in the phenolic compounds content, the oil kept most of its nutritional value. Considering that the average home cook will never cook anything for 36 hours straight, I think we’re pretty safe here. (6)

Another study compared insulin sensitivity in obese, insulin-resistant women when they consumed foods fried in extra virgin olive oil to meals that contained uncooked oil. This one surprised me as it compared the cooked vs. uncooked olive oil, and cooked won out. There was no difference in insulin sensitivity when the oils were eaten by lean subjects, however. This was a small study, but it’s intriguing to hear that perhaps the cooked olive oil may have some benefits over uncooked oil for some people. (7)

Being able to heat olive oil opens up cooking options, especially for those who are very sensitive to the effects of saturated fat on their cholesterol levels. If you’ve been hanging around for a while, you probably know that your cholesterol levels aren’t the end-all-be-all. However, those with familial hypercholesterolemia (and even those without!) will be happy to hear that they can cook with a fat that has been shown to reduce LDL oxidation, thus improving their heart health. (8)

How to buy and store olive oil

While the fact that olive oil contains mostly monounsaturated fatty acids is important, researchers believe that it is actually the phenolic compounds that stabilize the oil as it’s heated. This is why it’s vital that you purchase extra-virgin olive oil versus pure olive oil. Extra-virgin olive oil goes through less processing – it’s simply pressed and does not go under any heat or chemical treatment. Olive oil is one of the only oils that Americans still consume relatively unprocessed; most of the oils we buy are refined. Pressing the olives retains many more nutrients, including phenolic compounds, which we know serve to protect olive oil from heat. Even better is extra-virgin olive oil that hasn’t been filtered – the particles that cause the oil to be cloudy also act as antioxidants and buffers against acidity, thus protecting the oil from oxidation. (4)

That said, much of the extra-virgin olive oil bought in the United States is adulterated with other oils like soybean or rapeseed. That’s a bummer considering that many of us like to purchase our olive oil when we go to the grocery store. Thankfully, olive oil expert Tom Mueller has a list of extra-virgin olive oils you can buy at your local grocery store (including the real deal from chains like Costco, Trader Joes and Whole Foods). Make sure to check that out and if you’d like to learn more about this issue, read Mueller’s book Extra Virginity: The Sublime and Scandalous World of Olive Oil.

The other option, of course, is to source your own olive oil from a company you trust. If you live in a climate that supports olive growing, you might even be able to find a local company to buy from. If not, there are a plethora of options online, and it simply becomes a question of researching the company and preferably talking to a representative to see how they process the oil. A popular one in the Paleo community is Kasadrino’s olive oil – you can learn more about their company and values by heading to their website.

Once you’ve got your hands on a quality extra-virgin olive oil, take care to store it properly. Remember that heat is only one of the elements that causes fatty acid oxidation, the others being light and oxygen. You should store your olive oil in a cool, dark place in a dark airtight container. (Don’t buy olive oil that comes in a clear container, especially if you suspect it’s been sitting on the shelf for a while.) If you purchase large tins of olive oil, pour out what you’ll use in a few weeks into another dark bottle so that you can avoid opening the tin often and exposing the oil to oxygen.

Here’s the bottom line: extra-virgin olive oil is perfectly safe to cook with. It stands up well to heat due to its monunsaturated fatty acid and phenolic compounds content and fares much better than other vegetable oils. It’s a great oil to eat both in taste and health and shouldn’t be avoided. However, it’s not the only healthy fat out there! You should always consume a variety of healthy foods, fats included.

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