Over the past several decades, dietary fat has often held an undeserved “unhealthy” reputation.
While this mindset is changing in recent times, one particular fat—extra virgin olive oil—has long held a “heart-healthy” reputation.
Both scientific research and public opinion widely support the idea that olive oil has benefits.
However, some people believe we shouldn’t use extra virgin olive oil for cooking. Moreover, these are claims that it can even be harmful when exposed to high temperatures.
In this article, we examine this claim in more detail and take a look at what the research says.
Why Do Some People Claim We Shouldn’t Cook With Extra Virgin Olive Oil?
First of all, fatty acids are prone to oxidation from heat, light, and oxygen.
For this reason, the process of frying with oil can cause some of the fat to oxidize.
Furthermore, this oxidation process can lead to the production of secondary oxidation products like aldehydes and other polar compounds.
However, the specific fatty acids within a cooking oil play a significant role in how prone to oxidation a particular cooking oil is.
On this note, saturated fats are the most stable fatty acids, and hence, they are most resistant to oxidation (4).
Since olive oil is predominantly an unsaturated fat, many people assume it is not suitable for cooking.
The smoke point of oil—the temperature at which the oil starts to burn—is another metric that some people use to judge the merits of a particular oil.
However, The Fatty Acids In Olive Oil Are Reasonably Heat-Stable
Should we fear heating extra virgin olive oil? Let’s first look at the oil’s fatty acid breakdown.
According to the USDA Food Composition Database, extra virgin olive oil contains the following amounts of fatty acids per 100 grams (9);
- Saturated Fat: 13.8 g
- Monounsaturated Fat: 73.0 g
- Polyunsaturated Fat: 10.5 g
The first thing to bear in mind here is that not all unsaturated fatty acids are the same, and some are more heat-stable than others.
The Different Saturation Levels of Fat
Firstly, there are three primary groups of fatty acids, and these are as follows;
- Saturated fat
- Monounsaturated fat
- Polyunsaturated fat
All three of these fats contain the elements carbon and hydrogen.
In saturated fat, the carbon atoms are entirely “saturated” (surrounded) by hydrogen atoms, and the fat molecule contains no double bonds.
For this reason, saturated fatty acids are very stable, they rarely react with other molecules, and they are very resistant to oxidation (4).
The following diagram shows the molecular structure of saturated fat;
In contrast, monounsaturated fatty acids contain one (mono) carbon-carbon double bond and are not fully saturated with hydrogen. This double bond can be broken, which makes monounsaturated fat more prone to oxidation than saturated fat (10).
Here is the structure of a monounsaturated fatty acid;
Lastly, polyunsaturated fats contain multiple (poly) double bonds, and they are thus much more prone to oxidation than other fatty acids (11).
The diagram below shows one example of a polyunsaturated fatty acid which, in this case, has two double bonds;
While some cooking oils—such as soybean and sunflower oil—primarily contain polyunsaturated fat, olive oil consists of less than 10% polyunsaturated fatty acids.
Since olive oil is more than 90% saturated and monounsaturated fat, it is fairly resistant to oxidation.
The Smoke Point of An Oil Doesn’t Represent the Oil’s Oxidative Stability
Interestingly, many of us judge the relative benefits of cooking oil with a sole focus on the smoke point.
However, research shows that the fatty acids in cooking oil can breakdown before an oil even hits that smoke point.
For example, a recent study compared the chemical and physical changes in ten commercial oils while heating them at a temperature of 180°C (356°F) and various other heat/time tests (12).
These oils were as follows;
- Avocado oil (non-refined)
- Canola oil
- Coconut oil
- Extra virgin olive oil
- Grapeseed oil
- Olive oil
- Peanut oil
- Rice bran oil
- Sunflower oil
- Virgin olive oil
What Did the Study Show?
To directly quote the researchers;
“From this study, it can be concluded that, under different heating conditions, the generation of polar compounds with temperature and time was more pronounced for refined seed oils with higher initial values of smoke point” (12).
The term “seed oil” is another name for common vegetable oils (which are actually from seeds rather than vegetables) such as canola and grapeseed oil.
In contrast, olive oil is technically a fruit oil and, as previously mentioned, has a different fatty acid composition.
The table below shows the final amount of polar compounds each oil generated, as well as the oil’s smoke point in the test;
|Type of Cooking Oil||% Final Polar Compounds||Smoke Point (°C)|
|Avocado oil (non-refined)||11.60||197°C (387°F)|
|Canola oil||22.43||256°C (493°F)|
|Coconut oil||9.30||191°C (376°F)|
|Extra virgin olive oil||8.47||207°C (405°F)|
|Grapeseed oil||19.79||268°C (514°F)|
|Olive oil||11.65||208°C (406°F)|
|Peanut oil||10.71||226°C (439°F)|
|Rice bran oil||14.35||237°C (459°F)|
|Sunflower oil||15.57||255°C (491°F)|
|Virgin olive oil||10.71||175°C (347°F)|
As shown in the table, the smoke point of each oil had little relevance to the number of oxidation products the oil generated.
In other words; the smoke point of cooking oil is not a reflection of the oxidative-stability of the oil.
In this study, extra virgin olive oil generated a lower amount of polar compounds than any other cooking fat.
Extra Virgin Olive Oil Is Rich In Antioxidants and Polyphenols
Another point worthy of consideration is that extra virgin olive oil contains a wide variety of polyphenols as well as the antioxidant vitamin E.
Firstly, olive oil contains approximately 2 mg of vitamin E per tablespoon, which is equivalent to around 10% of the recommended daily intake (13).
Vitamin E has antioxidant properties, and research demonstrates that it can increase the resistance of fatty acids to oxidation (14).
Additionally, extra virgin olive oil is one of the richest dietary sources of polyphenols. The specific polyphenols include hydroxytyrosol, tyrosol, oleuropein, and oleocanthal (15).
Therefore, cooking with extra virgin olive oil is not the same as using ultra-processed vegetable oil.
Unlike such refined oils, extra virgin olive oil contains various compounds that help to protect the fatty acids from oxidizing.
What Does Research Show About Cooking With Olive Oil?
In addition to the research we have looked at so far, several other studies tested how olive oil performs when exposed to cooking temperatures.
Here is a summary of what these studies found;
- Compared to a commercial vegetable oil blend, frying with extra virgin olive oil led to reduced levels of oxidation. The vegetable oil blend was also much more susceptible to oxidation than any commercial olive oil sample (18).
- Much lower concentrations of aldehydes form when shallow frying fish in extra virgin olive oil compared to sunflower oil (19).
- In one trial, potatoes were deep-fried in either extra virgin olive oil, peanut oil, or canola oil. During the frying process, extra virgin olive oil formed fewer aldehydes and polar compounds than the other two oils (20).
- In a study featuring 20 participants, eating a breakfast fried with either canola or sunflower oil increased markers of DNA damage after the meal. On the contrary, breakfast meals fried in virgin olive oil did not (21).
- While not specifically related to cooking with olive oil, a randomized controlled trial found that extra virgin olive oil reduces the risk of cardiovascular disease and mortality. In this controlled study of 7216 people at high cardiovascular risk, every 10-gram increase in daily extra virgin olive oil decreased cardiovascular and mortality risk by 10% and 7%, respectively (22).
Extra virgin olive oil is primarily a source of monounsaturated fatty acids.
While not quite as stable as saturated fat, these fatty acids are more resistant to oxidation than polyunsaturated fats, and olive oil contains a range of protective compounds too.
Additionally, a range of studies shows that cooking with extra virgin olive is more beneficial than cooking with seed oils.
For these reasons, cooking with olive oil appears to be a reasonably good choice.
However, one thing to note is that there have been several scandals with olive oil in recent years. Unfortunately, there have been cases of adulterated oil falsely being passed off as extra virgin olive oil.
In some cases, these oils have simply been non-virgin olive oils, but in more serious cases, they have been cut with cheaper vegetable oils.
For more information on trustworthy olive oils, see this list of olive oils that submit to regular independent testing.