Olive oil is one of the oldest (and most revered!) edible oils out there, with culinary uses dating back to at least 1000 BC, and other uses scrolling back even further (such as anointing priests and kings). Not to mention, it’s versatile and delicious (olive oil ice cream, anyone?). Combined with mounting research suggesting olive oil is cardioprotective, it’s no wonder that this is one of the least controversial fats out there—given the green light by the Paleo community, vegans, vegetarians, low-carbers, the Harvard School of Public Health, and even the USDA. Not many foods can claim such widespread acceptance!
But, there is one area of ongoing debate when it comes to olive oil: cooking. Because it’s composed of mostly unsaturated fat (which is less chemically stable than saturated fat), many voices in the health community are claiming olive oil can become damaged when heated and lose its famed health benefits. In fact, some of the more extreme claims are that heated olive oil becomes legitimately toxic and can contribute to heart disease and cancer.
So, should we reserve olive oil for cold dishes only and nix it for cooking? As always, let’s look past the gossip and go straight to the science to find out!
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What’s the Problem?
Along with its high monounsaturated fat content, olive oil contains 1.4g of polyunsaturated fat (PUFA) per tablespoon (mostly in the form of linoleic acid), which is about 10% of its total fat content. Like all polyunsaturated fats, linoleic acid has multiple double bonds that are vulnerable to oxidation, especially when exposed to high temperatures (hello, fried foods!). Likewise, monounsaturated fat contains a single double bond, which makes it less heat-stable than saturated fats (though a definite step up from PUFAs) on the oxidation front.
So, in theory, we might expect olive oil to get pretty damaged when we expose it to heat on the stove. And with some reports of an olive oil smoke point as low as 250F, this would seem to provide corroborating evidence that olive oil should never be heated. The molecular damage from heating olive oil would erase many (if not all) of its beneficial properties and even make it somewhat hazardous to consume (since oxidized lipids in your diet can contribute to oxidized lipids in your blood—a big factor in heart disease). Scary, right?
Luckily for olive oil fans, the science shows something quite different!
What the Research Shows
A number of studies have been conducted on olive oil to assess the effects of cooking on its structure and nutritional content, as well as what happens in humans after olive oil is ingested.
Across the board, the research shows that even with a fair amount of heat exposure, extra virgin olive oil resists oxidation better than many other cooking oils. In one study, it took over 24 hours (a day straight!) of frying before olive oil generated enough polar compounds to be considered harmful. In another study, even after 36 hours of cooking, olive oil had retained most of its beneficial vitamin E content.
In fact, high quality (low acidity) extra virgin olive oil can have a smoke point as high as 410F. That’s higher than most cooking applications and makes olive oil (at least, the good stuff) more heat stable than many of our other go-to cooking fats!
The magic words here, though, are “extra virgin”: refined olive oils start to degrade in heat faster than their unrefined counterparts, and are overall more susceptible to oxidation (those are the ones with the low smoke point). The reason is due to extra virgin olive oil’s high content of antioxidants that protect the oil from damage in the face of heat or other oxidants. High-quality olive oils are very rich in at least 30 phenolic compounds with antioxidant activity—particularly oleuropein, hydroxytyrosol, tyrosol—as well as alpha-tocopherol, an important form of vitamin E. And, it turns out that olive oil’s phenolic acid content helps stabilize vitamin E in the presence of heat, explaining why even sustained cooking times don’t obliterate the oil’s nutritional value. (For more info on important phytochemicals like phenols, you can read my recent post here).
In fact, those same beneficial compounds that protect olive oil from oxidation also help protect human LDL particles from damage. A number of trials have shown that after consuming olive oil, LDL from people’s serum takes longer to oxidize and is more resistant to oxidation, suggesting a major benefit for heart disease risk. So, whatever potential harm could come from olive oil’s relatively less-stable structure (compared to saturated fats like ghee and coconut oil), it appears to be more than compensated by its awesome phytonutrient content!
Getting the Most Out of Your Olive Oil
In order to get olive oil’s powerful antioxidant properties (and therefore avoid some of the hazards of its more delicate chemical structure), quality is key! And unfortunately, obtaining high-quality olive oil isn’t always straightforward. Even brands labeled “extra virgin” can vary wildly in freshness, phenol content, and linoleic acid level, and the olive oil industry is notorious for deceptive labeling (the book Extra Virginity by Tom Mueller chronicles the whole saga).
So, how do you choose the best oil? A few simple tips can help:
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- Look for brands that list a harvest date on the bottle, which will tell you when the olives themselves were picked. The more recent the date, the better (no more than 12 – 18 months)!
- Always choose oils in dark glass bottles—never plastic or clear ones.
- Oils that were imported from other countries are more likely to be deceptively labeled (and even cut with non-olive vegetable oils—yikes!), so look for more local oils, especially ones from California, or domestic companies that are transparent with their Mediterranean sources and production practices.
- When tasting the oil, it should be pungent and peppery, even stinging the back of your throat a bit—that’s a sign of a high polyphenol content. Yes, I regularly sample olive oils to test for that peppery bite!
- Make sure the label says “extra virgin” and not “refined.”
- Fresher is better. Unlike vinegars or wines, olive oil does not get better with age.
Equally important is taking care of your olive oil so that it doesn’t oxidize before you even get to use it! For best results, store your olive oil in a cool, dark place away from light and heat (e.g., in the pantry instead of on the counter next to the stove). Even high-quality, properly stored olive oils can start to degrade after four to six months, so purchase your oils in smaller bottles to make sure you finish each one up while it’s still fresh. And, even though olive oil may be relatively stable when heated, keep in mind that any fat will eventually get damaged from high temperatures (and that high-temperature cooking can destroy some nutrients in the other ingredients you’re using)—so limit frying in favor of gentler cooking methods, like sautéing.
So there you have it! As long as your olive oil is fresh and rich in phenols, you can enjoy it as a cooking oil without worry!
Citations
Allouche Y. “How heating affects extra virgin olive oil quality indexes and chemical composition.” J Agric Food Chem. 2007 Nov 14;55(23):9646-54.
Casal S, et al. “Olive oil stability under deep-frying conditions.” Food Chem Toxicol. 2010 Oct;48(10):2972-9.
Covas MI, et al. “The effect of polyphenols in olive oil on heart disease risk factors: a randomized trial.” Ann Intern Med. 2006 Sep 5;145(5):333-41.
Marrugat J. “Effects of differing phenolic content in dietary olive oils on lipids and LDL oxidation–a randomized controlled trial.” Eur J Nutr. 2004 Jun;43(3):140-7.
Pellegrini N. “Direct analysis of total antioxidant activity of olive oil and studies on the influence of heating.” J Agric Food Chem. 2001 May;49(5):2532-8.
Prabhu HR. “Lipid peroxidation in culinary oils subjected to thermal stress.” Indian J Clin Biochem. 2000 Aug;15(1):1-5.
Ramirez-Tortosa CM. “Extra-Virgin Olive Oil Increases the Resistance of LDL to Oxidation More than Refined Olive Oil in Free-Living Men with Peripheral Vascular Disease.” J. Nutr. December 1, 1999 vol. 129 no. 12, 2177-2183.
Staprãns I, et al. “Oxidized lipids in the diet are a source of oxidized lipid in chylomicrons of human serum.” Arterioscler Thromb. 1994 Dec;14(12):1900-5.
Tuck KL & Hayball PJ. “Major phenolic compounds in olive oil: metabolism and health effects.” J Nutr Biochem. 2002 Nov;13(11):636-644.
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Visioli F. “Rusting the pipes: ingestion of oxidized lipids and vascular disease.” Vascul Pharmacol. 2014 Jul;62(1):47-8.
http://www.internationaloliveoil.org/
TPV Podcast, Episode 165, Chit Chat & Community
So I have researched that Costco brand Kirkland Organic Extra Virgin Olive Oil is a good option, would you agree with this?
Great article, thanks Sarah! I had been very worried since my mother loves to cook with olive oil despite my warnings to her not to heat it. Glad to know this is probably not a big of deal as I previously thought. Interestingly, I had always heard the more-refined oils had a higher smoke point. Can you direct me towards the citation that backs up that point? I’m in the process of creating a guide to oils and will need to update it in light of this contradiction. Thank you!! PS, I love your podcast with Stacey, and I just finished The Paleo Approach. It’s by far one of the best books on health and nutrition out there.
I’m lucky to live in CA where, at Farmers Markets, I can buy numerous locally produced very fresh organic EVOO. Even then, I primarily use it for dressing, dipping and plating and rarely use it cooking, unless it’s a very quick low heat sauté. I’ve found that Chosen Foods Avocado oil or Ghee are best/safest for higher heat cooking when I don’t want any hint of coconut flavor (otherwise different types of coconut oil, depending on how high a heat is needed, works well too). I’ver found that avocado oil is flavorless and doesn’t compete with other flavors.
So what is better to cook with Coconut oil or olive oil? Butter? Ghee? Lard?
http://www.telegraph.co.uk/news/health/news/11981884/Cooking-with-vegetable-oils-releases-toxic-cancer-causing-chemicals-say-experts.html
Wow, I had no idea there were olive oil frauds going on. I’m now very suspicious of extra virgin olive oils out there.. Gonna be careful this time. Thank you very much for the warnings and heads-up, Sarah!
I’m really glad to see that extra virgin olive oil is actually great for high temperature cooking. However, I have found it can be quite difficult to find quality olive oil these days. I saw that you recommended a brand you love, but I would really prefer to buy in person. Do you have any suggestions for brands or stores that carry quality olive oil that I could visit in person?
Hello, Sarah!
I just preordered a bottle of EVOO from Kasandrinos. Can’t wait to use it!
By the way, I have a big question. I hope you don’t mind and can help answer, please if you have the time because I know you are quite busy these days.
Okay, now, I know that ‘Extra Virgin’ OIive oil would be more ideal for sauteing and cooking in higher temperatures than refined, but what about oxidation from.. air? Say, for example I am going to use EVOO (about a tablespoon) in a blender that has hot vegetables that I am going to puree into a paste.. thankfully, due to the high antioxidants and vitamin contents of EVOO have, the heat coming from the cooked vegetables is nothing to be worried about, but what I’m worried about is the oxygen generated when the blender is pureeing the oil and the vegetables together at high-speed. Wouldn’t that oxidize the oil and damage the oil still?
What are your thoughts on this?
Thanks!
Olive oil oxidization occurs when heating olive oil, plan and simple no grey area.
Leave it to your salads with vinaigrette. If you have to heat oils, use virgin coconut oil that has been hard pressed and organic.
The chemical structure painted above is only ‘part’ of the total biological breakdown occurring.
Hi, are the harvest dates usually clearly listed as it is (like “Harvest Date: DD/MM/YYYY”) or are they encoded? I live in Singapore where everything is imported and I can’t find the harvest date listed on any EVOO product available here. Does that mean they’re all fakes?
Does EV avocado oil contain as much antioxidants as EVOO and work just as well for cooking? I’ve tried EV macadamia nut oil before but noticed it smokes rather easily, and I wasn’t even cooking with high heat.
Very helpful, thank you – but Still confused! What are some temperature limits to watch out for? I cook veggies in the oven at 400 degrees with olive oil on them, and I use it for sauteing but I don’t know what temps that can reach. I often see smoke, but it seems unavoidable! Like maybe it’s just the veggies steaming? And coconut oil smokes more easily correct? Have I been doing this wrong? What are some tips for maintaining temperature when cooking with olive oil? Thank you for sharing all of this information!
After a little further reading around, I discovered in multiple places the obvious answer to one of my questions that I was oblivious to: smoke will smell smoky and steam will be clear and smell like the food being cooked. Somehow discerning the difference between the two isn’t so easy for me… but more more research for me as I realize this is more of a food science blog rather than cooking tips. Unless anyone reading this has any tips?
Oh this is such good news. I mean, lard and duck fat makes some amazing roasted veggies, but with my genetics, the saturated fat does worry me. I’m glad I have permission once again to cook with olive oil–especially fresh, reliably sourced, extra virgin. Thanks for doing the research and a great article!!