Awhile back some of we cooking instructors and nutrition nerds got in a snit about olive oil and whether it was “safe” to heat it. I was prompted to seek a definitive answer when one of my students, who was vegan, was perplexed by what fat to use to make a cookie. Butter was out and for whatever reason coconut oil wasn’t working for this student. She was considering extra virgin olive oil (EVOO in Rachel Ray jargon). I wrinkled my nose thinking about the taste of an olive oil cookie. But this person had trepidation because “heated olive oil will oxidize and be toxic to my body”.
Really? Could that be? How did this student garner this particular fear? And did it have any validity? Shouldn’t Rome have fallen much sooner if this was the case?
I went for the big guns – Dr. Mark Kestin, PhD in nutrition and a mind like a biochem data base.
Here’s his answer:
“Firstly, as you probably already know, the smoke point of a cooking fat or oil is the temperature at which the chemical bonds between the fat molecules (trigyclerides) begin to break down and get turned into other compounds. EVOO has a low smoke point as it has a little water and some other stuff in it. All this means is that you should not deep fry with EVOO but you can sauté or bake with it – think of it a little like butter which also has a low smoke point.
Secondly, when you overheat an oil, and especially if you use it again and again for deep frying, the polyunsaturated fatty acids get oxidized and make a number of substances, some of which may be carcinogens, but definitely affect the flavor, texture, color etc. As olive oil does not have many polyunsaturated fats it is less likely to do this than say sunflower or canola oil. But considering you shouldn’t be deep frying with it in the first place it is not really a practical problem.
Thirdly, EVOO has some unique compounds (the chemicals are called phenols) which are believed to have specific health effects separately from the monounsaturated fat. There is less work done on how stable these compounds are. I have seen two or three studies that found that shallow frying with EVOO led to about 30% loss of the compounds in total (80% was lost if the oil was used for frying 8 times). To put this in perspective, this is less than the loss of vitamin E and if you store EVOO for 4-6 months in the dark you lose about 40% of these compounds (and you lose about 60% if stored in diffuse light). However, some of these compounds are more fragile than others but we don’t know enough to say which is most important for health effects.
My take overall is that baking or sautéing with EVOO should be OK if you don’t reuse it. It may be more important not to store too long and to keep it in the dark.”
So that’s my overall take too. Thank you Dr. Kestin. Slays me how we have to prove that the simple way we have made food taste fabulous for centuries is safe. Of all the things out there that truly could be labeled “toxic” I’m running around defending a beautiful bottle of organic EVOO. Silly rabbit.