Soon after, we received a letter from a reader that prompted us to dig deeper into the important issue it raised.
The results were a bit surprising, and very encouraging for the EVOO-loving cooks among us, so we’d like to share the letter, and our response, with you... both are edited slightly here.
I have always tried to use extra virgin olive oil as a cooking oil for frying or sauteeing until I read an article by Sheryl Crow (a breast cancer survivor) who said that her nutritionist said olive oil has carcinogenic properties at high temperatures and canola oil was a better choice.
What's your take on using EVOO for cooking with heat? I enjoy the newsletter.
Here's how we replied to Bob's question:Dear Bob:Your question prompted us to search the biomedical literature, with some surprising, encouraging results. So we’re glad you asked!In short, the evidence suggests that it’s very safe to cook with extra virgin olive oil (EVOO) at temperatures of 300-350 degrees, which is substantially hotter than the range usually given.Most consumer guides advise people to limit use of EVOO to temperatures of 250-320 degrees F, but they present no evidence for this, nor can we find any in the scientific literature.In fact, studies show that EVOO is remarkably resistant to damage when heated as high as 400 degrees, as for frying foods. Still, it may be unwise to make a habit of that, and it’s certainly not the best use of a fine EVOO.Here’s what we found, in detail.EVOO is very safe for cooking… within reasonThe fatty acids in any oil heated to the point of smoking will be structurally damaged and will generate DNA-damaging oxygen radicals in the body (If an oil smokes during cooking, discard it and any food cooked in it).But an oil’s smoke point may be higher than the temperature at which damage occurs to its fatty acids, and in this respect, all olive oils offer a distinct heat-resistance advantage.Most common cooking oils
– such as corn, canola, soy, safflower, and sunflower
– have smoke points that range from 400-450 degrees, but they are also very high in heat-sensitive omega-6 fatty acids.
Compared with omega-6-rich oils, olive oil of any grade is much lower in heat-sensitive omega-6 fatty acids, and much higher in heat-resistant monounsaturated fatty acids: sturdier fats that also make olive oil notably healthier than its omega-6-rich counterparts.
It’s instructive to note that in one study, men suffered less oxidative damage to their LDL cholesterol after eating olive oil (grade unspecified) that had been heated to 410 degrees F for eight hours, versus eating safflower oil treated the same way: a sure sign that the olive oil suffered less oxidative damage at this temperature.
Canola oil is frequently touted as a safer alternative to EVOO and other oils for high-temperature uses.
While canola oil has more heat-resistant monounsaturated fats than other common oils, it remains quite high in heat-sensitive omega-6s. And unlike any other cooking oil, it has considerable amounts of short-chain omega-3s, which are even more vulnerable to heat damage compared with omega-6s.Thanks to its almost uniquely high proportion of stable monounsaturated fatty acids
– macadamia nut oil rivals it in this regard
– the smoke point of refined, “Pure” grade olive oil (also labeled simply “olive oil”) is about 460 degrees, which is higher than most omega-6-rich oils.
Of course EVOO is different from Pure grade olive oil, because, in addition to containing antioxidants not found in Pure grade olive oils, it contains non-fatty compounds that can burn (oxidize).
Even so, the International Olive Oil Council sets the smoke point of EVOO at 410 degrees, which is as high as most omega-6-rich oils.
Since the hottest temperature needed for deep-frying – for frying quick-cooked foods like small fish and croquettes – is 375 degrees, EVOO could be used for this purpose, as it is throughout North Africa and the Middle East.
However, we would suggest that you not fry foods in EVOO at temperatures over 350 degrees for more than 10-15 minutes, and that you consider using a refined, Pure grade olive oil for frying instead.
In fact, Pure grade olive oil is preferable to other oils for deep-frying. This is because its high monounsaturated content won’t let it penetrate foods as deeply as standard, omega-6-rich oils, so it yields leaner, less caloric fare.
EVOO’s mixed bag: oxidation-enablers vs. oxidation-enemies
Extra Virgin Olive Oil (EVOO) may be a bit more vulnerable to heat damage compared with Pure grade olive oil, but the common presumption that it is much less sturdy than omega-6-rich oils seems unsupported by the available evidence.
Unlike Pure grade olive oils or “Virgin” grade olive oils – which are blends of Pure and EV grade oils – EVOO retains most of the antioxidant phenols, chlorophyll, and other non-fatty compounds natural to olives (Pure grade olive oils contain virtually no antioxidants or other non-fatty compounds).
The antioxidants and other non-fatty compounds in EVOO offer benefits and drawbacks with regard to the ability of fatty acids to resist being oxidized during exposure to cooking temperatures over 350 degrees… countervailing forces that probably cancel each other out:
EVOO’s downside: “auto-oxidizing” agents
EVOO contains chlorophyll and other non-fatty, non-antioxidant compounds that oxidize pretty easily once exposed to air and high heat, and during extended exposure to light.
Once oxidized, these compounds generate free oxygen radicals that accelerate oxidative damage to the oil’s fatty acids: a process called “auto-oxidation”, since it begins with compounds found in the oil.
EVOO’s advantage: self-protecting antioxidants
The antioxidants in EVOO protect its fatty acids from oxidation pretty effectively. The results of two studies indicate that EVOO is remarkably resistant to oxidative damage, even when it’s used for deep-frying (i.e., heated to about 360 degrees for 10 minutes).
EVOO loses 20-50 percent of its dihydroxyphenol-class antioxidants after one deep-frying episode, so it shouldn’t be used for frying more than once. The lost antioxidants include hydroxytyrosol, which is virtually unique to olive oil and is one of the most powerful food-borne antioxidants ever tested.
But EVOO retains almost all of its moderately powerful tyrosol antioxidants even after 12 deep-frying uses. And only after six uses for frying do the levels of oxidized fatty acids in EVOO rise rapidly. These findings suggest that EVOO is far from the wilting violet many sources presume it to be.
The vulnerability of an EVOO’s fatty acids to oxidation depends to some degree on the amount of naturally occurring protective antioxidants in it: a variable that depends on the species of olive, the source fruit's ripeness when picked, and the maximum temperature generated in the oil during mechanical “cold-pressing” of EVOO from olives.
(There’s no way to know the exact antioxidant content of any given bottle of our certified-organic Spanish EVOO, which probably varies a bit from batch to batch and from season to season.
But its full, fresh flavor and the gentle, low-temperature pressing methods used to extract it from the olives suggest that our EVOO is probably relatively rich in fatty acid-protective antioxidants.)
Go easy on the heat and keep it in the dark
To ensure maximum health value and flavor, we recommend that people primarily use EVOO in two ways:
- For dressings and dips, and added to dishes after they’ve been cooked, for flavor and artery-protecting nutrition.
- For cooking at temperatures of 350 degrees or less – i.e., for sautés and sauces.
And it's critical to protect EVOO from light, which degrades the oil’s fatty acids and flavor quite rapidly.
Always keep EVOO in a dark place at room temperature or lower, and use it within 10-12 weeks of opening.
Or, keep it in your refrigerator, where it will last a full year. Chilled EVOO will become cloudy, with no harm to its flavor or nutrition value. Just bring some to room temperature before using it for dipping, or in dressings and other uncooked foods.
We hope this answers your question, Bob!
- International Olive Oil Council at http://www.internationaloliveoil.org/index2.html
- Kalua CM, Bedgood DR Jr, Bishop AG, Prenzler PD. Changes in volatile and phenolic compounds with malaxation time and temperature during virgin olive oil production. J Agric Food Chem. 2006 Oct 4;54(20):7641-51.
- Kalua CM, Bedgood DR Jr, Bishop AG, Prenzler PD. Discrimination of storage conditions and freshness in virgin olive oil. J Agric Food Chem. 2006 Sep 20;54(19):7144-51.
- Luna G, Morales MT, Aparicio R. Changes induced by UV radiation during virgin olive oil storage. J Agric Food Chem. 2006 Jun 28;54(13):4790-4.
- Gallina-Toschi T, Cerretani L, Bendini A, Bonoli-Carbognin M, Lercker G. Oxidative stability and phenolic content of virgin olive oil: an analytical approach by traditional and high resolution techniques. J Sep Sci. 2005 Jun;28(9-10):859-70.
- Rastrelli L, Passi S, Ippolito F, Vacca G, De Simone F. Rate of degradation of alpha-tocopherol, squalene, phenolics, and polyunsaturated fatty acids in olive oil during different storage conditions. J Agric Food Chem. 2002 Sep 25;50(20):5566-70.
- Andrikopoulos NK, Dedoussis GV, Falirea A, Kalogeropoulos N, Hatzinikola HS. Deterioration of natural antioxidant species of vegetable edible oils during the domestic deep-frying and pan-frying of potatoes. Int J Food Sci Nutr. 2002 Jul;53(4):351-63.
- Gomez-Alonso S, Fregapane G, Salvador MD, Gordon MH. Changes in phenolic composition and antioxidant activity of virgin olive oil during frying. J Agric Food Chem. 2003 Jan 29;51(3):667-72.
- Deiana M, Rosa A, Cao CF, Pirisi FM, Bandino G, Dessi MA. Novel approach to study oxidative stability of extra virgin olive oils: importance of alpha-tocopherol concentration. J Agric Food Chem. 2002 Jul 17;50(15):4342-6.
- Ramirez-Tortosa MC, Urbano G, Lopez-Jurado M, Nestares T, Gomez MC, Mir A, Ros E, Mataix J, Gil A. 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. 1999 Dec;129(12):2177-83.
- Gutierrez F, Jimenez B, Ruiz A, Albi MA. Effect of olive ripeness on the oxidative stability of virgin olive oil extracted from the varieties picual and hojiblanca and on the different components involved. J Agric Food Chem. 1999 Jan;47(1):121-7.
- Sutherland WH, de Jong SA, Walker RJ, Williams MJ, Murray Skeaff C, Duncan A, Harper M. Effect of meals rich in heated olive and safflower oils on oxidation of postprandial serum in healthy men. Atherosclerosis. 2002 Jan;160(1):195-203.