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Is it safe to cook with olive oil?

September 15, 2012
Let’s check the science: Is it true that olive oil turns toxic at high temperatures? 

A friend was recently told by her GP that she should not cook with olive oil because, he claimed, it becomes toxic when heated. In our house, we cook with olive oil all the time because we know it’s healthier than butter or other saturated fats, so this would have serious implications for us. Do I need to switch to another oil for cooking?


This article assumes you are happy to accept science as the best way of discovering the truth about the natural world. If that’s not the case for you, why not have a look at Trusting the science first?

Cooking in oil

The promoters’ arguments – science or red flags?

Strangely, I could find very few websites encouraging the view that olive oil is worse than any other oils in this respect. Here’s a typical extract from one of those:

DANGER: Don’t Cook with Olive Oil!
That’s right, you read it correctly, do not cook with olive oil because it’s dangerous to your health.  Numerous scientific studies show continually that olive oil is one of the best sources of the Omega oils that YOU NEED for a healthy nervous system and cardiovascular system…BUT what they often neglect to tell you is that those wonderful BENEFITS ARE ALMOST COMPLETELY DESTROYED once you heat the oil!  That’s right, the process of heating oils can cause the fats to become carcinogenic; which means causes CANCER!  Heating causes enzymes to be destroyed, proteins are denatured, fats become carcinogenic, carbohydrates (sugars) become caramelized, vitamins and minerals become less available, and water is eliminated.

Most websites, though, were quite sensible and gave the advice that all oils deteriorate when heated, and olive oil is about average in this respect. They generally assured me that there was nothing to worry about (e.g. here). Given that my friend’s GP was so concerned, I had expected to find more anti-olive oil information.

Do I see any red flags? Well, the excerpt above misleads because contains exaggerations and straw men and tries to frighten us with them. Heating food does destroy enzymes, denature proteins, caramelize sugars and reduce water, but that is irrelevant because olive oil contains practically none of those substances. In any case, we cook foods precisely because we want these things to happen. That’s what makes them tastier and more easily digested.

Being skeptical

My nonsense detectors always go into overdrive at the mention of toxins. They are among the favourite bogeymen of bogus scientists (along with radiation and negative energy). There are lots of toxins in our environment. Many foods contain substances that are toxic, and cooking can produce more. Our bodies have evolved to be quite good at dealing with the odd toxic molecule that manages to find its way inside. It even produces and eliminates toxins of its own.

It’s important to realise that just about anything (yes, even water) can be toxic to us in large enough doses. So there’s no need to panic at the thought of ingesting a small amount of a substance that, in large amounts, could poison us. Our bodies are quite used to dealing with this situation. I suspect this is probably the case with any toxins produced when olive oil is heated.

Still, my friend’s GP would have been aware of all of this, so I’m interested to see what my research reveals.

The scientific evidence

This is a complex issue to investigate. Luckily, I have a background in chemistry, so I was able to follow fairly well most of the papers I discovered. Here’s what they told me:

  • Vegetable oils oxidise as they age and are exposed to air and light. This process is accelerated when they are heated (here, here).
  • Some of the oxidation products are toxic (here, here, here and here), but (here) we have good natural defences against such substances.
  • The ease of oxidation of an oil is influenced by its degree of unsaturation. Polyunsaturated oils oxidise more easily than saturated oils  (here).
  • Corn oil and sunflower oil contain high proportions of polyunsaturated oils; they oxidise easily. Coconut oil is high in saturated oils; it doesn’t oxidise easily.
  • Olive oil contains a high proportion of monounsaturated oil. It oxidises less easily than polyunsaturated oils (here, here).
  • Virgin and extra-virgin olive oils also contain antioxidants which help resist oxidation as the oil is heated (here, here and here). Several studies have shown that virgin olive oil produces fewer oxidation products than polyunsaturated oils when heated (here, here)
  • If an oil is heated beyond its smoke point, it gives off toxic smoke. The smoke point of olive oil is around 200°C. Some refined oils, such as palm, peanut, safflower and soybean oils can have smoke points around 230°C to 260°C, but unrefined oils can have smoke points in the low hundreds.
  • I could find no studies showing evidence of damage to the health of humans resulting from oxidation products of cooking oils.

Conclusion

My initial skepticism was pretty-well confirmed by my research. Olive oil certainly doesn’t deserve to be singled out as a source of toxins in cooking. There are oils that are far worse, and in any case, as long as I don’t use extreme temperatures or cooking times, the amount of oxidation product will be small. My body should be able to deal with it easily. I’ll continue to use olive oil (preferably extra-virgin) for cooking, but I’ll do it sensibly.

Further reading

Health Check: cooking oils to eat and avoid at The Conversation.


Photo credit: SINC

This is one of ScienceOrNot’s Let’s check the science series.
61 Comments
  1. Thanks for this Graham. To my shame, I must admit that, I have been concerned about stories I had heard (that the goodness of olive oil is negated by heating it up). Nevertheless, I clearly need to get the thermostats on my (halogen/ceramic) cooker fixed because they seem to be either off or on full power at the moment; and are clearly getting my (extra virgin olive) oil hotter than in needs to be. So, please excuse me while I go and sit inside my Reiki Pyramid to de-toxify myself…. ;-)

  2. Great exposé! There should be prison time for those who propagate junk science!

    • julie permalink

      bullshiiiiiiiit the one talking shit is the guy who wrote the article. he just wrote some bla bla here 2 cover our eyes. first of all only illiterate people dont know that all oils except palm oils release toxins when cooked which are carcinogenic. and this idiot is tryin 2 minimize the effect of toxins. well after uve eaten only shiit food for years and years, then u get strange symptoms and surprise ur diagnosed with cancer when ur just 40 or 50 then maybe u really understand the importance of these “boogeymen.” especially virgin or refined olive oil can cause cancer bc of the compounds it releases when being made. then, when heating it even the extra virgin one is causing harm. check this website http://www.whfoods.com/genpage.php?tname=george&dbid=56 and dont listen 2 this guys nonsense. im tired of “skeptical” people tryin 2 look scientific and not recognizing the harm of this kind of things or hydrogenated fats or genetically modified food. open ur eyes or are u witing 2 be dying and rolling in pain while u wait ur death?

      • Julie, thanks for your response but the link you provided provides rule-of-thumb type information and not one reference from a credible scientific source. Ignoring that, the page you cite basically says that oil smoking indicates that it’s decomposing and that potentially dangerous oxygen radicals are produced. That same article also says that some olive oils do not smoke until heated above 350° F, the temperature I deep fry at (I saute at an even lower temperature), so this tells me that as long as my olive oil isn’t smoking, go ahead and fry something in it.

        Palm oil may not be the perfect oil… consuming its palmitic acid has been implicated in increasing the risk of developing cardiovascular diseases [see: Diet, Nutrition and the Prevention of Chronic Diseases, WHO Technical Report Series 916, Report of a Joint WHO/FAO Expert Consultation, World Health Organization, Geneva, 2003, p. 88 (Table 10)]. Some of the social, environmental, and economic issues of palm oil production do not paint too rosy a picture, either. The fact is, just about anything we choose to eat has can have a negative effect on the environment, other people, and even our long-term health.

        “This guys [sic] nonsense” looks to me to be well-researched and referenced nonsense. Even the sources he cited cite their sources as published peer reviewed studies. (I didn’t go through them all but the ones I looked at had them). Where are you getting your info? The whfoods.org article you sent me to didn’t provide references.

        Why don’t you start up your own WordPress blog and convince us of whatever you believe, but please write in something approximating Standard English unlike your comment above… it will make things so much easier for us “illiterate people” who dont [sic] know all oils except palm oils release toxins when cooked” who write “ur” as “your”, etc. I’ll be your first subscriber.

        • ^ Served! Haha. Julie’s rant was cacophonous, painful to read and perhaps the most carcinogenic thing that has, and will ever happen on this blog. Unconfirmed rumors overheard in the locker room during third period say that everyone who read it now has a 20% to 50% chance of getting cancer unless they only use their cell phones right side up for the next 30 years.

          • Thanks, James. The way I see it, from the time we’re born we’re living on borrowed time. We spend our lives weighing what we want to do vs. what we should do to increase our chances of making it into the next hour. You can meticulously research the optimal diet and exercise combination, surround yourself with people who love you and live wherever it is that has the population with the greatest statistical longevity but a little freezing rain can cause a tractor-trailer to slip and crash through the front wall of your house only to mash you to a pulp while you’re counting calories in your living room. I eat what I want and don’t BASE jump—that’s how I achieve balance.

            It’s too bad Julie didn’t go on and point us toward some real information as to why genetically modified food is bad for our health and not just a political issue. I keep hearing those big diesels and hope to see some real data damning GMOs.

      • Gimlich Stormsetter permalink

        Yes, I too am tired of all these “skeptics” talking all fancy with their “science”. They throw around their numbers and statistics as “evidence”. Evidence of what?! More deception! Logical Fallacies? More nonsense. I’m with Julie, let’s stand up to all this logical science based reasoning and help plunge our society back into the dark ages!! Who’s with us?!!

  3. Just think!…
    More than 80% of Greek recipes based on extra virgin olive oil and the main oil for frying is olive oil.
    Now….
    Greece has one of the highest life expectancies worldwide and one of the lowest cancer rates too!
    This is because of the mediterranean diet and the consumption of olive oil (26 litres per Greek person per year!)
    Facts are the best answer to all these nonsense articles!

    • I understand your enthusiasm, lakonia olive oil, but you do have a vested interest and of course, anecdotal evidence is not reliable, nor does correlation prove causation.

      • “Cockledoodle-doo!”

        • Yes, lakonia olive oil, I’m sure there are some legitimate studies in there that counter my comment about anecdotal evidence. And I’m quite convinced about the health benefits of olive oil. However it’s still the case that correlation doesn’t prove causation and I see red flags in your list of links. For example, your second link employs the ‘scientifically-proven’ subterfuge.

          • I have just picked them by searching google, only few from numerous scientific articles about olive oil just to prove you that what I am saying is not anecdotal(Greek word by the way..) evidence…
            Anyway…to have some kind of problem with olive oil you have to reach the smoking temperature, which is 208C or 406F. To fry in these temperatures (normally 160C or 320F) you must be a very bad cook or you want to put your house on fire…

          • I think if you read the papers I refer to in my article you’ll find that reaching the smoke point is a different issue from oxidation, which can occur at lower temperatures. But you are right, there is nothing to worry about if you use common sense in your cooking. On a separate note, it’s difficult to justify saying (as you did in your initial comment) that the Greek’s long life expectancy “is because of the mediterranean diet and the consumption of olive oil”, since RCT’s can only show correlation and in-vitro and animal studies may non translate to humans

          • Update 2013/04/15: A recent study (here) gained a huge amount of publicity because it claimed to show once and for all that the Mediterranean diet prolonged life. However, major flaws have been pointed out in this study (here, here).

            Further update 2013/09/25: Ah, this is what we want. A new systematic review (here) concludes that:

            greater adherence to Mediterranean diet is associated with slower cognitive decline and lower risk of developing Alzheimer disease.

          • julie permalink

            when ur rolling on the floor with last degree cancer that noone can cure and even morphine doesnt take away the pain maybe ud wish ud forget about ur bullshit skepticism for “anecdotal” evidence. the medical industry and pharmaceutical companies are labeling whatever they want as “anecdotal” and “not proven”, especially the natural remedies. i ve been eating all my life almost everyday raw onion and garlic and thank god i havent caught a cold in like 4 years. there have been many cases that showed the power of plants curing diseases and the importance of eating healthily and raw foods.the pharmaceutical world is just after the money and thats why doctors dont openly admit genetically modified food causes cancer, although its “suspected” . well sometimes we use our common sense if we have a brain: what is not natural anymore and modified isnt hard to believe that can modify also the organism it went into. but if noone wants 2 bring out a real proof, bc like this more than 50% of stuff sold in supermarket couldnt be there anymore people happily ingest all shit because its “not proven 2 be bad 4 u, just anecdotically”. well, u have a brain, make ur own choices and then ull have 2 take the consequences.. i dont really have the time 2 do research online and post it here but i think my arguments make sense. maybe when i have more time ill post more& ull think in a different way…its ur choice anyway and im not tryin 2 convince u, im following my way and my diet. oh and i dont think the greeks fry so much,. i think their health benefits come mostly from UNCOOKED olive oil. so dont fool urself that if ur gonna fry all day with olive oil everything will be dandy,. check better and ull find all oils except palm produce toxins that can cause cancer. NOT BULLSHIT, NOT BOOGEYMAN, JUST CHEMICAL COMPOUNDS IF U PREFER NOT TOXINS THAT CAN CAUSE CANCER. LOOK INTO THAT

          • Eric permalink

            Julie – No one is going to take you seriously. First of all, you appear to be illiterate. You write with the skill of a 5 year old who hasn’t had any writing experience outside of texting. Your grammar and spelling is atrocious. Secondly, if you don’t have time to do a little internet research on peer reviewed studies then you have no business being in this conversation. Why are you even wasting your time, considering those two points? If you want people to believe what you are saying merely as an opinion, with no credible scientific research to back your assertions, you need to at least write eloquently; you are dimensions away from that. There is more to science than opinion. As was stated earlier: Correlation does not imply causation. You talk about people using their brains? You are showing here that you barely have one, and you make comments like that. Shameful. You need to work on your brain a little. Good luck. You’re going to need it.

  4. Helen permalink

    Stumbled upon this site when I was googling which oils to heat/not and the validity of this argument. Thanks for doing the research for me! Every article that I could find in support of NOT heating olive oil led me to the Mercola site. That’s quite a red flag, to me. I have a friend who goes a little nuts with her “research-based” health posts and almost always references articles on that site. Do you have any insight into it? They tout themselves as being “The World’s #1 Natural Health Website.” I’m bookmarking your site, btw.

    • Thanks for the comment, Helen. I can do no better than refer you to some of the websites I trust most for their opinions of Dr. Mercola:

      Science-based medicine: here (“… there are very good reasons why a competent science-based physician would prefer that his patients have nothing to do with Dr. Mercola, who runs what is arguably the most popular and lucrative alternative medicine website currently in existence and manages to present himself as reasonable simply because he is not as utterly loony as his main competition, Mike Adams of NaturalNews.com … and Gary Null.“) and here.
      Quackwatch: here (“Many of Mercola’s articles make unsubstantiated claims and clash with those of leading medical and public health organizations.“)
      Respectful Insolence: here (“He might have been a real doctor at one time, but in 2012 he exists only to enrich himself by selling a mixture of the unremarkable, the unproven, and what I consider to be quackery.“) and here (“Joe Mercola: 15 years of promoting quackery“.)
      Skeptical Raptor: here (“So Mercola just ignores real science, and decides that whatever random words he uses would mean more than evidence..”)

      • Helen permalink

        Wow, that sounds about right. Thanks!

        • julie permalink

          OH WOOOW hes a genius…not…if he encourages people 2 eat fried olive oil…while all oils except palm release chemical compounds that can cause cancer.research that. and i see this guy has a lot of free time 2 post so-called “reliable sources”. ill make some time 4 this: a whole day to put out here research that shows fried olive oil is CANCEROUS LIKE ALL OILS EXCEPTPALM

      • M.B permalink

        Your articles posted to discredit Dr Mercola would only be taken in by the ignorant of the masses.

        All the sources basically are in favour of conventional-based medicine as being ‘real-science’ and ‘proven’ treatments. And they are using the same deceptive, straw-man based discrediting techniques to ridicule Dr Mercola for his unconventional approach to treatment.

        They call him a ‘quack,’ just like they call any other physician who uses alternative forms of treatment that is not patented by the Pharmaceutical Corporations who have the monopoly of the medical industry.

        Of course any alternative natural form of treatment is going to be considered as ‘unproven’ and ‘quackery’ despite their safety and efficacy by the Pharmaceutical Corporations, because:
        1) They cannot patent natural forms of treatment – so there is no money in it for them.
        2) They only fund trials that are based on allopathic treatment which is patentable and no major clinical trials are funded by them on the effectiveness of natural remedies.

        Therefore, natural treatments would never be considered as ‘proven’ by mainstream medicine, as no Corporation would fund a trial that they cannot profit from it’s treatment in the long run.

        So by using articles that are advocating mainstream science as reference on Dr Mercola – I expect nothing less from them but to discredit him as they are not going to discredit themselves and destroy their own multi-billion allopathic drug sale industry are they.

        And whatever money Dr Mercola is making from his websites, it is nothing in comparison to the allopathic pharmacy industry – who by all means have everything to lose if people were more educated on natural treatments. A conflict of interest anyone? By default your references on Dr Mercola are lousy and garbage.

  5. Luke McCallum permalink

    oxidation occurs within the cellular structure of humans…eating oxidized foods is NOT the same is cellular decomposition inside our bodies….expulsion of oxidized foods probably takes up more energy, influencing the GI tract to work harder than it needs to..and this makes me curious of what the body loses when doing so (I bet there’s a stage if re-building the oxidized food). Harm to human health? No…loss of nutrients? Severely…Coconut Oil a great substitute for cooking? Absolutely. But when the doctor speaks of this cold pressed oil becoming “rancid” due to the acceleration process, well…it’s really fermenting which in some food enriches Probiotics…and after doing some research on the breakdown of unsaturated fats to tranfats there’s an an enzyme needed to break down the bond further (multiple oxidations), and after heated up, killing the enzymes, it does NOT turn into a transfat.
    “lakonia olive oil permalink

    Anecdotal evidence…” Does indeed point out the beta oxidation is done in this fashion with cooking, but more importantly the body finishes the complete oxidation process of the unsaturated fat.

    “Peroxisomes…are membranous sacs in cytoplasm containing powerful oxidase enzymes that use molecular oxygen to detoxify harmful or toxic substances” Also…”oxygen is reduced to water (H2O) or hydrogen peroxide (H2O2).
    The oxidases are a subclass of the oxidoreductases.”

    These enzymes are also used to identify bacteria that react with the utilization of the transfer…so consider the fermenting process creating Probiotics, the oxidation, and peroxisomes…hmmm…are you sure some oxidized food you eat isn’t helping your immune system more than by giving you a little extra boost of Omega 3 oil?

    For all practical scientific purposes of ,this article…cooked food loses nutrients..and you need to study biology more before posting absurd doctor claims about his dislike for olive oil.

    • Luke McCallum permalink

      to elaborate on this part of my quote… Also…”oxygen is reduced to water (H2O) or hydrogen peroxide (H2O2).” Rehydration keeps unsaturated fats from completely oxidizing and can repeat the process in an infinite loop.

    • That is the most comprehensive reply for this article! Thank you Luke

  6. Passerby permalink

    Gah…I hate seeing perfectly commonsensical things get twisted into “Oh noes! You’re going to DIE!” propaganda. Yes, heating the oil causes it to break down. Yes, you lose a lot of the touted health benefits by heating it before consuming. Does that mean it turns cancerous? No. What nonsense.

    What REALLY bothers me is that this doesn’t even sound like something someone made up to scare people into buying a rival product…this sounds like someone with woefully poor scientific literacy read a couple of different weblogs, added 2 + 2 and got 17.

    But really people, olive oil’s low smoke point just makes it a poor choice of cooking oil. Save it for the vinagrattes and marinades, cook with something else.

  7. shagufta permalink

    Today a lady scared me to death , by saying same cancer stuff, i have been using extra virgin olive oil for long , she got pretty emotional and told me its so lethal and blah blah.
    i decided to do research myself …i am satisfied now.thank you

  8. You spent zero time discussing the major biochemical concern with cooking with olive oil: unsaturated oils contain cis-double bonds. Heating oil can increase the rate of conformational change to the more stable trans conformation. What do you have to say about trans-fats?

    • Also, please do not repeat the very terrible confusion that isomerization and oxidation or hydrogenation are the same thing.

    • What makes you think that this is a major concern with olive oil, Corey? Trans fats certainly form under these conditions, but I wouldn’t think it’s of major concern. Here‘s a study that shows an increase in trans content from 0.045% to 0.082% after 8 cooking cycles. Do you have any figures that would indicate we should be more concerned?

  9. Nice article, I notice there was a correlation in your article between olive oil and “other” vegetable oils… which could be further considered that Olives are linked to vegetables because they are vegetables. Perhaps it’s the phrasing of words or how it’s being iterated that lead me to think this way.

    But Olives are actually a Fruit and Olive Oil is a fruit based oil.

    All vegetable oils in general are bad for you.

    • I used the term “vegetable” in the sense of contrasting with animal and mineral, Jen. Most common mineral and animal oils are saturated and consequently don’t oxidise as easily as oils that are extracted from plants, which tend to be unsaturated.

      “All vegetable oils in general are bad for you” is a rather sweeping statement. Can you give us some evidence to back it up?

  10. patty permalink

    I’m still confused. Does cooking/ frying with ANY oil–corn, canola olive etc.. for a long time (using the same batch over and over like in a restaurant) or at high heat (like frying chicken) cause it to become a trans fat?????
    If we are not to cook with olive oil, then which is the safest one to use?

    • Saturated fatty acids can’t produce trans forms because they don’t contain carbon-carbon double bonds, Patty. Animal fats, coconut oil and palm oil contain high proportions of saturated fatty acids. Fatty acids containing carbon-carbon double bonds (monounsaturated, such as the main ones in olive oil, or polyunsaturated) do produce small quantities of trans fatty acids when heated strongly, but it’s in very small amounts (here, here, here, here) The process that really increases the trans fatty acid concentration is partial hydrogenation, an industrial process that’s used to raise the melting temperature of polyunsaturated oils.
      I’d encourage you do do some research of your own into the issue. You might like to consider the trade off between the health risks of trans fats vs saturated fats.

      • John permalink

        Graham,

        You have not answered patty’s questions.

        Please pay attention and answer them. All you did was offer a red herring as a solid straw man that you beat up. You then told patty to go and research the answer self because I think you what you did – you did not answer the question but offered logical fallacies.

        When done, please answer my questions as well:
        Is it ok to use Olive oil to fly and cook food in?
        Is it ok to use butter to fly and cook food in?
        If none of the two above are ok, then what is?

        And by ‘ok’ I mean just that ‘ok’. You can read this as healthy and place any conditions on it (just note these) and explain the risks.

        Answering with non-destructive assumptions is not what anyone wants to read.

        Thank you.
        John

        • John,
          I disagree. You are wrong on two accounts.
          First, I’ve quite explicitly answered patty’s question.
          Second, there are no red herrings or straw men to be seen in my reply. In fact, I find your entire carry-on about logical fallacies difficult to understand.

          I don’t run this website as a question-answering service. Articles such as this one are written as examples, hopefully encouraging readers to carry out their own investigations into scientific issues. That’s why I encouraged patty to indeed proceed that way.

          Please don’t come here and make demands. It won’t be regarded as helpful. It seems that English is not your native tongue, and if the curt manner of your commenting stems from this, I can understand, but please try to be more polite.

  11. Mel permalink

    My understanding is that pure olive oil does not contain transfatty acids. If an olive oil labelled at Extra Virgin contains 0.2g/100 ml trans fats would that imply that it has either been heat processed or has some other (unlisted) oil blended with it?

    • Either of these could explain the trans content. I’m not familiar enough with the chemistry of olive oil to say whether there could be other reasons, but they would be the most obvious.

  12. Uhm, Hey. You seem to have missed a fairly major distinction, and that is between cold pressed extra virgin and virgin olive oil (which have more healthy- yet unstable at heat- elements) and refined olive oil. Refining any oil makes it less likely to produce (supposedly unimportant to you) ‘toxins’. For example of what happens when you cook to high-temperatures with unrefined oil, see Shields, P. G., Xu, G. X., Blot, W. J., Fraumeni, J. F., Trivers, G. E., Pellizzari, E. D., . . . Harris, C. C. (1995). Mutagens From Heated Chinese and U.S. Cooking Oils. Journal of the National Cancer Institute, 87(11), 836-841.

    • The article above does distinguish between virgin and refined oil, edibleangela, in that the former has more antioxidants which helps reduce oxidation products during heating. Refining does produce oil with a higher smoke point but I’ve already addressed this in some of the comments. I’d be interested to see your references for claiming that “refining any oil makes it less likely to produce ‘toxins'”. The paper you refer to (available here) is interesting. It shows that, yes, oils produce dangerous substances when heated, which isn’t in dispute. It has little to do with olive oil, apart from the fact that it tested linoleic acid, a minor component of olive oil.

  13. Alyssa permalink

    I’ve thoroughly enjoyed reading your post..however I still have a concern about cooking with olive oil. I heard that non-stick pans contain chemicals that can harm us when used, & I have been using a non-stick pan with olive oil for a long time now before I heard about that. Would it be safer to use an Olive Oil Pam spray on a stainless steel pan? Or am I fine using the non-stick pan with olive oil at medium heat? By the way, I don’t use a lot of olive oil..I’ll use a very small amount to spread around the pan to cook eggs and fish.

    • JRich permalink

      I do not recommend Olive Oil Pam as it contains propellants and they are not the healthiest way to get your olive oil. Use a mister and spray the olive oil in the stainless steel pan.

  14. chemist permalink

    This notion that olive oil turns into a carcinogen is complete and utter B.S.!!! There is absolutely not a shred of evidence in any peer reviewed journal demonstrating this claim. Fresh, high quality extra-virgin olive oil with low Free Fatty Acid (0.1-0.3%) high polyphenol content (>300ppm) can tolerate heat up to ~420F before smoking. This temperature range is perfect for sauteing or baking. I’ve also heard some whackos spewing the notion that heat changes the chemical structure of the MUFA to an undesirable fat (trans, etc…). Again this is complete B.S.!! If one pushes any oil to smoke then all bets are off but this IS THE CASE FOR ALL OILS and not limited to fresh EVOO!! Even if an oil smokes there still is not a shred of evidence that the oil becomes a carcinogen! It always amazes me why anyone would want to consume an oil that has smoked? A few very simple rules to prevent any oil from smoking- Place enough oil to coat food into an appropriate size pan. Heat oil over medium-medium high heat. When oil begins to pull apart (shimmer) add food. The addition of food will reduce the oil temperature and off you go. If you start with a fresh EVOO (high MUFA content) and cook within its cooking range you are using the best oil possible in regards to health benefits.

  15. Nana Yao permalink

    “It is not what you do, but rather, how you do it,…”
    This is a very topical look at this issue. You have not carried out enough research nor are you a medical practitioner, nor have you had to diagnose or treat any of the millions of disability adjusted life persons living with the multitudes of diseases caused by miss-uses of fats and oils. You speak in general terms, but you fail to mention being in the middle it has both the dangerous aspects of low risitance to heat and contains monosaturats which react to heat and pick up significant enviromental contaminants. Besides, I have always known as reised by family that olive oils are best as flavouring and salad oils. Cooking oil is specified as such because it is prepared to be safer for cooking. Where as olive oil is not in any way form or manner procesed to be able with stand the pressures of cooking.
    Frying is the main form of cooking with oil, and I would like to know how many of us check the tempreture of the bottom of the pan when we fry. It usually goes over 200°C. How many of us throw out a whole pan of food “simply” because a bit of burn occurred and a bit of smoke which we bearly notice has emanated from the cooking pan.
    The advise is; cook with as little cooking oil as possible. Then when done and flame / heating stove is turned off, then add your flavour oil such as olive oil, peanut, almond oils…etc. Thus their good prorerties will take full effect and their hamfull properties will not be activated. This way the oxidents generated from the innitial little bit of cooking oil used would be counteracted by the anti-oxidents of the olive oils and their similies.
    Knowledge should lead to understanding, which in turn should lead to wisdom. Wisdom is determined by your actions.
    Wishing you all a happy Live Well With Health.

  16. Ashley permalink

    I suspect the GP gave the warning since most people aren’t able to recognize when the oil hits the smoke point, or think of it as ok. Also extra virgin has a lower smoke point–which is tricky since someone might think they’re being healthier, and inadvertently reach the smoke point if solely cooking with extra virgin. I love cooking with virgin olive oil, but I save the extra virgin for after heat, and if I need to go above 200C I use a different oil :) No smoke point, no problem.

  17. Danielle permalink

    Thanks for the interesting article! I too was skeptical about these claims but admittedly I’m starting to reconsider after coming across the following studies on PubMed:

    Genotoxic and carcinogenic risks associated with the consumption of repeatedly boiled sunflower oil – http://www.ncbi.nlm.nih.gov/pubmed/20886885
    Genotoxic and carcinogenic risks associated with the dietary consumption of repeatedly heated coconut oil – http://www.ncbi.nlm.nih.gov/pubmed/20687968
    The effects of heated vegetable oils on blood pressure in rats – http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3226610/
    Hypertension is related to the degradation of dietary frying oils – http://www.ncbi.nlm.nih.gov/pubmed/14668269/

    These studies do seem to indicate that (at least certain types of) oxidised oils can be harmful. It’s interesting to see that coconut oil is among them, when that seems to be touted by all of the anti-olive oil crowd as being the ‘safe’ oil to use.

    I’d love to hear your opinion!

    • Thanks for the links to these studies, Danielle. I haven’t had a chance to read them all, but I’m not surprised at the findings. Heating of any oil is going to produce oxidation products and the more heating, the more contamination. So all of these studies appear to show that the more repeatedly heated the oil is, the greater the physiological effect. And as you’d expect, small amounts of oxidation products (from mild heating) can be handled pretty well by our bodies. I look forward to reading the articles more fully.

      • John permalink

        Graham,

        Hopefully you have read these articles that Danielle posted.
        Can you please share your opinion or beliefs of these. It would actually be great if you can convert your opinion & beliefs into knowledge by referencing your falsifiable evidence and independent sources.

        I look forward in your reply.

        Thanks
        John

      • John permalink

        Thanks Graham,
        I see you deleted my two comments.
        What is the name of the logical fallacy when you silence your critics?

        • Your comments were awaiting moderation, John, while I was in an isolated region with no internet access. They were not deleted. If they had been, I would have informed you by email, and given reasons. As I’ve suggested in reply to one of your earlier comments, please try to be more polite.

  18. Lynn Perkins permalink

    I enjoyed reading the article. I found Julie’s comments to be quite entertaining. I for one, find her to be anything but scholarly. She does not present herself as any type of professional. Her grammar is terrible. I agree that she writes like a fifth grader.
    I enjoyed the scholarly writings that included credible references. Thanks for the information!

  19. Abhilasha permalink

    Thank you for this. I’m not a science student, but I get it. Now, I want to go explain it to the two airheads I met at the grocery store who literally tried to convince me not to buy extra-virgin olive oil. Nonetheless, I bought it. Like I have been since years.
    Your article helped. Thank you. :)

  20. I thought I was allergic to eggs because I love them scrambled, but about ten years ago I started having optical migraines with visual auras every time I ate them. This led me to believe that I had developed an allergy to eggs. Later, I tried using tofu to scramble like eggs and shortly after experienced an optical migraine! This leads me to believe that I am not allergic to eggs, but, rather, another ingredient I’ve been using to scramble them. One of those is olive oil which I used for both the scrambled eggs and the scrambled tofu. I used to use Crisco or margarine long ago before I developed the migraines. Does anyone know if there are any chemicals in olive oil or in heated olive oil that might cause migraines? I would love to find out I could eat eggs again by using a different oil! I hate to experiment with this because optical migraines are rather scary — you see jagged lines and lose vision for a period of time. Thank you for any help!

  21. Doug permalink

    I do all my cooking on cast iron to avoid the poisions. I heat the olive oil to about 210° F, just begins to shimmer. The stove top setting is 4 (medium is 5). I use the oil once only. Scrub the pan afterwards and re-oil. Delicious.
    My chol and trigylcerides have dropped in half. Think I’ll maintain course and speed. My Grandfather is 92, says its the olive oil (I think its the olive he puts in his martini).

  22. Joe Dirt permalink

    One cannot reconcile an outdated myth such as the erroneous presupposition: “In our house, we cook with olive oil all the time because we know it’s healthier than butter or other saturated fats”… with Science-based anything. This is the same ‘eat low-fat/unsaturated fats or no butter/salt/eggs’ propaganda that has been destroyed by science again and again, yet surfaces in well-meaning posts like this, resulting in the continued epidemic of obesity, cancer and diabetes. Not just irresponsible, but reckless too. Learn something and start over. I bet you had good intentions but the time for niceties has long passed, along with the victims of this type of advice ;)

Trackbacks & Pingbacks

  1. The veggie-meat adventure. | Eclectic Lunatic
  2. Not All Oils Are Created Equal | Well-Woman
  3. “Get Well” Chicken Soup | Blissfully Informed Hippie Chick

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