Another myth debunked: Heating EVOO makes it ‘toxic’admin | September 20, 2013
One of the most enduring myths about extra virgin olive oil is that if you heat it then it will produce more free radicals (and is therefore be more ‘toxic’ – or more appropriately ‘detrimental to your long term health’) than other edible oils.
The belief in the binary model of ‘EVOO when heated is ‘toxic’, but every other fat when heated is not’ is plainly ludicrous. Why? Because the natural chemical composition of all edible fats including EVOO overlap, and in some cases significantly. For example while EVOO contains on average around 75% of the fatty acid oleic acid, canola oil averages around 60%, and high oleic sunflower about the same or higher than EVOO. All oils contain sterols and tocopherols, and while EVOO has significantly more polyphenols than any widely used edible fat, polyphenols are more likely to inhibit the formation of free radicals Therefore unless the oil extracted from olives is somehow able to find a way to defy the basic laws of fat chemistry, then the idea that olive oil becomes more ‘toxic’ than other oils when heated can’t be justified.
Recently a paper was published in the peer reviewed journal Food Chemistry (Tomassetti et al. 2013) which goes a long way to debunk the myth.
What they did:
- A peanut oil and extra virgin olive oil that had been stripped of its polyphenols were heated to 180C and air was bubbled through them over a period of hours in an effort to mimic extreme heating conditions
- Heating peanut oil and EVOO (even without antioxidant polyphenols) resulted in the same degree of free radical formation. (Figure 1).
- The longer you heated these edible fats the more free radicals they formed – both of them!
Tomassetti et al. (2013) PO=peanut oil, EVOO=polyphenol stripped extra virgin olive oil. If the error bars shown at the top of the bars overlap then that means that there is insufficient evidence of a difference in free radical formation between the oil types upon heating.
What they did:
- A peanut oil and an EVOO (with its natural polyphenols) were heated and compared with respect to rancidification.
- More heat energy was needed to start the oxidation of fat molecules in EVOO than peanut oil which suggests that EVOO is more resistant to rancidification when heated. The authors attributed this to the polyphenols in the EVOO. “the higher thermal stability of triglycerides contained in the whole EVOO is probably due to the high concentration of polyphenols contained in it”
The researchers used an EVOO stripped of polyphenols as phenolic compounds interfered with the measurement of free radical production. Given that polyphenols mop up free radicals, I would predict that the net production of free radicals in heated phenolic rich EVOO would be significantly lower compared with refined edible fats that contain few if any phenolic compounds.
The oils were heated to a reasonable cooking temperature. They were not burnt! Once an oil burns a whole different bunch of chemical reactions come into play. So is burnt EVOO any more or less healthy for you than burnt edible oil X? Probably not, but who cares.Just don’t use burnt oil of any type. It isn’t good for you. That is what the knobs on the front of the stovetop are for.
Tomassetti et al. (2013) Biosensors for monitoring the isothermal breakdown kinetics of peanut oil heated at 180 C. Comparison with results obtained for extra virgin olive oil. Food Chemistry, 140, 700-710.