Last week, we ran an article about the central role that extra virgin olive oil (EVOO) plays in providing the benefits of the “actual” Mediterranean diet – as opposed to the idealized version tested in many nutrition studies (see “Mediterranean Myths: Region's Actual Diets Differ from Ideal”).
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.
Bob's question
Randy,
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.
Cheers,
Bob
Our answer
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 reason
The 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 heart-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 -- macadmia 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, and it is used for frying 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.)
