Olive oil is extremely healthy.
It is the "default" healthy fat... loaded with beneficial fatty acids and powerful antioxidants.
Olive oil has also been a dietary staple for some of the world's healthiest populations.
That being said, there may be a problem with olive oil...
Many people believe that it is unsuitable for cooking because of the unsaturated fats.
I used to believe in this myth, but after doing more research I realized that I was mistaken.
Today, I'd like explain why olive oil is an excellent choice for cooking, even for high heat methods like frying.
When fats and oils are exposed to high heat, they can become damaged.
This is particularly true of oils that are high in polyunsaturated fats, including most vegetable oils like soybean and canola.
When cooking with these oils, some of the carcinogenic compounds actually vaporize and may contribute to lung cancer when inhaled. Therefore, just being present in a kitchen where these oils are used can cause harm (3, 4).
If you want to minimize your exposure to harmful and carcinogenic compounds (always a good idea), then it is essential to cook only with fats that are stable at high heat.
There are two properties of cooking oils that matter most:
- Smoke Point: The temperature at which the fats begin to break down and turn into smoke.
- Oxidative Stability: How resistant the fats are to reacting with oxygen.
As I will outline below, olive oil does pretty well in both regards.
For more info about choosing the right fats/oils, check out this detailed article about the healthiest cooking fats.
Bottom Line: It is very important to choose cooking fats that are stable when heated, because some oils can form carcinogenic compounds during cooking.
Each fat molecule (triglyceride) consists of a glycerol molecule linked to three fatty acids.
All glycerol molecules are the same... but there are hundreds of different fatty acids in nature and the health effects vary between them.
Fatty acids can be either saturated, monounsaturated or polyunsaturated.
Saturated fatty acids have no double bonds, monounsaturated have one (mono = one) and polyunsaturated fatty acids have many double bonds (poly = many).
Here's the important part... the double bonds are unstable when heated and they tend to react with oxygen.
Therefore, the more double bonds a fatty acid molecule has, the more unstable it will be when used for cooking. This is the reason saturated fats (zero double bonds) like coconut oil are very resistant to heat (5).
Although most vegetable oils contain polyunsaturated fatty acids with many double bonds, olive oil contains mostly monounsaturated fatty acids with one double bond.
As it turns out... having one double bond in the fatty acid molecule is not a bad thing. It's only the polyunsaturated fatty acids (like those in soybean and canola oils) that are harmful (6).
Of course... oils are usually a mix of different types of fatty acids. Olive oil, for example, is 73% monounsaturated, 11% polyunsaturated and 14% saturated (7).
In other words, the heat resistant monounsaturated and saturated fats make up 87% of olive oil.
Bottom Line: Olive oil contains mostly monounsaturated fatty acids, which are actually pretty resistant to heating. Damage-prone polyunsaturated fats make up only about 11% of olive oil.
The only olive oil I recommend is extra virgin olive oil.
Vitamin E's main purpose is functioning as an antioxidant within the body. There, it helps fight free radicals that can cause damaging chain reactions in our cell membranes (10).
Because olive oil is high in antioxidants and Vitamin E, it has quite a bit of natural protection from oxidative damage (11).
Bottom Line: Olive oil contains Vitamin E and many powerful antioxidants. These substances protect the oil from damage during high heat cooking.
When an oil oxidizes, it reacts with oxygen and forms various harmful compounds.
This can happen at room temperature and is one of the ways oils go rancid, but this process is greatly accelerated when oils are heated.
An oil's susceptibility to oxidative damage depends primarily on two things:
- Its concentration of polyunsaturated fatty acids, which tend to oxidize (react with oxygen).
- The presence of antioxidants, which counteract the oxidative damage (that's why they're called anti-oxidants).
As outlined above, olive oil is low in polyunsaturated fatty acids (about 11%) and high in antioxidants.
Numerous studies have exposed olive oil to high heat for long periods of time and measured how it affects the quality and nutritional properties of the oil.
Many of these studies used a high temperature for a very long time. But even under these extreme conditions, olive oil did pretty well.
One study deep fried several different types of olive oil for 24 hours and noted that it was highly resistant to oxidation. Extra virgin olive oil, which is higher in antioxidants, did the best (12).
Other studies agree with this... olive oil does not oxidize much when used for cooking, while vegetable oils like sunflower oil do oxidize and form harmful compounds (13).
However... one study showed that eating a meal with heated olive oil increased oxidative markers in the blood compared to a meal with unheated olive oil (14).
In this study, the olive oil was not extra virgin and it was cooked for 8 hours... so this may not applicable to a real world situation, especially not if you're cooking with real extra virgin olive oil.
It is also a myth that heating olive oil leads to the formation of trans fats. In one study, frying olive oil 8 times in a row only increased the trans fat content from 0.045% to 0.082%, still a negligible amount (15).
Overall... it appears that olive oil is very stable, even under extreme conditions like deep frying for extended periods of time.
Bottom Line: Many studies have exposed olive oil to high heat for long periods of time. Even under such extreme conditions, the olive oil does not form significant amounts of harmful compounds.
The smoke point of an oil is the temperature at which it starts to degrade in the heat and produce visible smoke.
When this happens, the fat molecules are getting cleaved into glycerol and individual fatty acids, while also turning into various harmful and potentially toxic compounds.
But the other trace nutrients in the oil, like the vitamins and antioxidants, can also start to burn and give off smoke, sometimes at lower temperatures than the oil itself.
Usually, a portion of the fatty acids in an oil are free and not attached to glycerol. These are called free fatty acids. The more free fatty acids there are in an oil, the lower its smoke point.
Because refined oils are lower in trace nutrients (a bad thing) and lower in free fatty acids, they usually have a higher smoke point.
Also, when the oil is heated, more free fatty acids form in the oil, so the smoke point actually goes down the longer you cook it.
It is difficult to determine an oil's exact smoke point, because it doesn't happen all at once. There is a range in which a higher temperature forms progressively more smoke.
Many of the numbers for smoke points you will find on the internet are just estimates. The numbers vary between different batches.
Many sources put the smoke point of extra virgin olive oil somewhere around 375-420°F (190-215°C). Refined olive oil is often placed around 468°F (242°C).
This makes it a safe choice for most cooking methods, including most pan frying.
Bottom Line: Extra virgin olive oil's smoke point is somewhere around 375-420°F (190-215°C). This makes it a good choice for most cooking methods.
Normal cooking use is unlikely to oxidize or significantly damage the oil.
However, it may degrade some of the antioxidants and Vitamin E, which are sensitive to heat.
In one study, heating olive oil at 356°F/180°C for 36 hours did lead to a decrease in antioxidants and Vitamin E, but most of the trace compounds were intact (16).
One of the main active compounds in extra virgin olive oil is called oleocanthal. This substance is responsible for olive oil's anti-inflammatory effects and the burning sensation in the throat that quality olive oil brings (17).
Heating olive oil at 464°F/240°C for 90 minutes reduced the amount of oleocanthal by 19% according to a chemical test, and 31% according to a taste test (18).
The trace compounds in olive oil are also responsible for some of its flavor. Therefore, overheating olive oil can remove some of the taste.
Keep in mind that the studies showing that heat degrades olive oil's antioxidants and vitamins are using rather extreme conditions.
Quality extra virgin olive oil is a super healthy fat that retains its beneficial qualities during cooking.
The main reason you may not want to use it, is that heating it too much can have adverse effects on the flavor.
The belief that olive oil oxidizes and goes rancid during cooking is a harmful myth that scares people from using this incredibly healthy fat.