Researchers at the University of the Basque Country in Spain studied olive, sunflower and flaxseed oils for their aldehyde content after heating the oils to 190℃. The conclusion once again debunked the myth that frying with olive oil is unsafe.
See more: Dispelling the Myths of Frying with Olive Oil

It is a wide-spread belief that frying food in vegetable oil can be unhealthy because of the toxic chemicals (called aldehydes) produced in the process. Aldehydes are organic compounds containing a carbon-oxygen double bond, which are formed naturally in the human body in small amounts. Consuming an excess of aldehydes is thought to contribute to the symptoms of diseases like diabetes.

The results showed that the polyunsaturated (sunflower and flaxseed) oils produced higher amounts of aldehydes at a faster rate than monounsaturated (olive) oil. The olive oil created fewer aldehydes and also at a later stage of the heating process. The reason for this is thought to be because polyunsaturated oils contain more regions for chemical reaction compared to monounsaturated oil. Comparing the results, it is safe to say that olive oil is actually the best option for frying.

Experiments conducted for the BBC show Trust Me I’m a Doctor confirmed this by suggesting that heating monounsaturated fats like olive oil, butter, and goose fat produce lower levels of aldehydes than heating polyunsaturated fats and oils.

However, it is important to note that we know little about what a too high dose of aldehydes in humans constitutes. Thus far, conclusions have only been drawn from animal studies, and there is a lack of data from human studies that can be drawn upon to support theories.

Experts argue that the potential risk also depends on the quality and freshness of the oil, and how much it is heated. It can only be said that frying foods in shallow amounts of olive oil for short periods is unlikely to lead to exposure to aldehydes that is in far greater amounts than what the body would normally produce and it does not pose a greater risk than frying with other oils. It has also been suggested that olive oil’s high antioxidant content may even reduce the amount of possibly harmful chemicals produced during heating.

Any oil that is heated beyond its smoke point will contain harmful chemicals. However, this type of heating (or burning) will also significantly affect the taste and smell of the oil. Frying foods usually does not get the oil to that point.

Frying foods, in general, is known to be the least healthy method of preparation, however using olive oil may be safer than using other vegetable oils.


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