When does heating olive oil become “carcinogenic”?

When does heating olive oil become carcinogenic is a topic of conversation I hear too frequently. The media (including social media platforms) seem to be fear mongering the population into thinking that cooking with olive oils are bad for our health and “carcinogenic”. You have probably heard phrases like, “Extra virgin olive oil should only be used as a dressing because when it is heated it becomes toxic” and “cooking with coconut oil is the best as it has the highest smoke point”. However, this is not what the research suggests.

Olives and olive oil

Extra virgin olive oil has been linked to improved heart health and is a staple in the Mediterranean diet. It is rich in phenolic antioxidants and monounsaturated fats which are shown to improve heart health. Most of all, extra virgin olive oil’s distinct flavour makes it a great oil to use in the kitchen. So, why the negative press?

The fear comes from an oils “smoke point”. When oils are cooked past their “smoke point”, it is feared that they release chemicals which are harmful. Consumers are concerned that if they cook with olive oil or extra virgin olive oil that any original health benefits would be destroyed, or become toxic.

Extra virgin olive oil is the most chemically stable oil after heating at high temperatures, and safe to consume.

Acta Scientific Nutritionl Health – 2018

Research published in 2018 by Acta Scientific Nutritional Health found that when compared to other popular cooking oils, extra virgin olive oil was the most chemically stable after heating at high temperature. In addition, despite being exposed to extreme high heat it was still safe to consume. The tests consisted of a 20-minute frying at 240C and a 6 hour deep frying at 180C.

In both tests extra virgin olive oil came out on top with the most stable of all oils and produced the lowest number of by-products such as free fatty acids. Coconut oil and other virgin oils such as avocado oil came close behind for stability and smoke point.

The research shows that smoke point does not correlate with toxicity of oils. The more stable an oil is depends on its levels of antioxidants and monounsaturated fats, not the temperature at which is begins to “smoke”.

It is also demonstrated that oils must be heated at extreme temperatures for long periods of time to show any degradation. Even still, the healthier the oil, the more stable it behaves. High stability of an oil slows the breakdown and release of toxins which may be a health concern. To put this into consideration, the Food and Chemical toxicity study published in 2010 found that when various olive oils were fried for 24-27 hours, this is when the oils were considered to be harmful. That is above and beyond any roast potatoes or fried tofu you might have cooking in the kitchen.

It is also suggested that cooking foods rich in antioxidants in olive oil can also have some added benefits. Research published in 2015 “Food and Chemistry study” found that when deep frying vegetables such as tomatoes, aubergine and squash, the antioxidant levels of the food increased! This shows that despite heating, olive oil continues to deliver nutritional benefits even when deep fried.

Do bear in mind that when smoke points are measured, these are done so in laboratories, an enclosed environment with very small amounts of oil to test. Exposure to air and the amount of oil used when cooking can increase an oils smoke point which means that by the time the oil has reached your pan, the smoke point is likely to be above what it states.

An olive tree with light green olives growing
An olive tree with light green olives growing

To conclude, I just want to stress that although smoke points are there to highlight how an oil responds to high heat, it is not an indicator of an oils stability or health value. I hope that after reading this it makes you rethink your fear of cooking with olive oils and allows you to enjoy the amazing oil that it is. Extra virgin olive oil is the most stable and healthiest oil there is, and despite coconut oil coming second in the Acta study, its high saturated fat content would make it a lesser choice in the kitchen. Opting for the other close runners, avocado oil and rapeseed, would be a greater alternative.

Now, go and enjoy your olive oil roasted potatoes!