Updated: Apr 18
By Wageningen Beasts
A common myth is that you should not use extra virgin (olive) oil for baking. This myth states that this might be bad for you due to trans-fat formation, and that the taste will adversely change. Is there a healthier alternative? Is this myth true or not? Keep on reading to find out!
What are trans fats?
Trans fats are unsaturated fatty acids, of which the geometric configuration (the way the atoms are ordered in the fat) is different from (cis-)unsaturated fatty acids that we are familiar with. As can be seen in the picture below, both fatty acids have exactly the same atoms in the same order. The only difference is the placement of the hydrogen atoms (H) at the double bond (indicated with the red and blue circle). At the cis-bond, the hydrogen atoms are at the same side of the carbon chain, and at the trans-bond, the hydrogen atoms are at the opposite side. This small structural difference could cause big differences in important factors such as the melting point, and can thereby explain differences in healthiness between trans fats and non-trans fats.
Processes such as heating can change the configuration of a bond from cis to trans. In other words: heating of unsaturated fats can result in trans fat formation. This is only possible if fats contain a double bond. Since saturated fats do not have a double bond, trans fat formation can only occur in unsaturated fats.
Regulation of trans fats Since the 1950s, trans fats have been abundantly used in the food industry. Trans fats do not only occur naturally in foods, but are also a byproduct formed by production processes such as hydrogenation of vegetable oils (a process during which liquid oils are converted to solid or semi-solid fats). The latter form is called artificial trans fat. It is generally known that artificial trans fats are bad for health. Consumption increases the risk of multiple cardiovascular risk factors and coronary heart disease events such as heart attack and stroke. It is for that reason that use of artificial trans fats was banned in 2006 by the FDA. Trans fats occurring naturally in animal products are also thought to be unhealthy, but they are probably not as worse as artificial trans fats (and trans fat levels are also much lower compared to food products containing artificial trans fats). Thus, it can be concluded that trans fats are unhealthy.
Oil baking/frying and trans fat formation Trans fats are also formed by heating of vegetable oils, such as olive oil. Especially during deep-frying, a lot of trans fat formation will occur. However, this trans fat formation predominantly occurs at high temperatures (150-200+ degrees Celsius). Therefore, baking or stir-frying with vegetable oils hardly induces trans fat formation, even not at high temperatures as confirmed by this study. Thus, baking with oil in general will be safe with regard to trans fat formation.
Differences between extra virgin/refined What is the exact difference between extra virgin olive oil and refined olive oil? Oil is produced by the extraction process of vegetables and seeds, such as olives, sunflowers, rapeseed, and so on. There are many different names for each oil. There is refined olive oil, virgin olive oil and extra virgin olive oil (and some other examples on which we will not go into detail). The difference between these oils is the degree of processing and thereby the quality of the oil. Extra-virgin olive oil is of the highest quality, followed by virgin olive oil and lastly refined olive oil. The word virgin indicates that the olives were pressed in order to extract the oil. This is the purest form of oil, and thus has the highest quality. This is different from refined oils, which have been produced by chemical or heating processes after the olives are pressed to create virgin oil. Thus, the big difference is the amount of nutrients and the sensory properties (or in other words, the taste).
Both refined and (extra) virgin olive oil are high in poly unsaturated fatty acids (PUFAs), which are healthy compared to saturated fats. Thus, cooking with oil is always better than cooking with butter(based) baking products, as these contain more saturated fats and less PUFAs. Additionally (extra) virgin olive oil contains a lot of polyphenols (e.g. vitamins E and K, phytosterols and polyphenols), which have been proven to have protective health effects with regard to cardiovascular diseases[4,5]. A lot of these compounds function as antioxidants. Thus, extra virgin olive oil is the best choice to consume, as this is the most healthy one.
What happens when extra virgin olive oil is heated? It is often said that when extra virgin olive oil is heated during baking, the taste changes and trans fats are formed. This would not be the case for refined oils.
Firstly, like previously stated, heating oils at low temperatures (like temperatures during baking) cannot (or hardly) produce trans fats. The only difference between extra virgin oil and refined oil is quality and nutrients. It would therefore be weird that trans fats would be formed when baking with extra virgin, but not with refined olive oil. Thus, we can safely assume that no trans fats will be formed when baking with extra virgin (olive) oil.
Nonetheless, there are some changes occurring in the extra virgin olive oil during baking, otherwise the taste would not change. Some of the antioxidants in the oil are thought to be degraded during baking. I could not find studies looking exactly into this problem. Most studies are looking at changes in extra virgin olive oil due to deep frying. In addition, the total amount of polyphenols in the oil consists of a lot of different compounds, of which many we did not identify yet. It is therefore difficult to measure all the polyphenols, so answering the question how many polyphenols are degraded due to baking proves to be difficult. From my personal point of view, I don’t believe that all the polyphenols present in the oil will be degraded by baking shortly with oil, as these temperatures are relatively low and heating duration is short. Therefore, even though some of the polyphenols are lost, there are still more polyphenols remaining than when cooking with refined oil in which hardly any polyphenols are present. With this respect, extra virgin olive oil would still be a healthier choice to bake with. A study that investigated the effect of heating on antioxidants and polyphenols in virgin olive oil confirms this hypothesis. This study showed that the antioxidants present in the oil have a protective effect on polyphenols. In other words, heating degrades antioxidants while most of the polyphenols are spared and still intact.
However, it is true that heating extra virgin olive oil changes the taste of the extra virgin olive oil. You have to decide for yourself whether you think this is a problem or not. Extra virgin oils have a more distinctive taste than refined oils. This characteristic taste will change. I myself do not have a sophisticated taste. I therefore do not mind if the distinctive taste of extra virgin oil is changed during the baking. I do not taste much difference between baking with refined oil or extra virgin olive oil. I care more about the health properties. Think of it like this: If you are baking with refined oil, the taste is of less quality than extra virgin olive oil. When baking with extra virgin olive oil, the taste does not get worse than refined oil, so you might as well choose to bake with extra virgin oil since it’s healthier.
Concluding: not baking with extra virgin oils? Myth! Let’s summarize what we have found:
Baking with extra virgin oil does not produce trans fats.
When baking with extra virgin oil some antioxidants (polyphenols) are lost, but most of the polyphenols will still be present in the oil.
The taste of extra virgin oil may be affected by heating. You should decide for yourself whether you find this important.
Thus, when approaching this health-wise, the myth that you should not use extra virgin olive oil for baking is not true.
Disclaimer: In this article I only talk about baking and not about deep-frying. When you are deep-frying, olive oil is not a good choice as a lot of trans fats will be formed. In this case more stable oils such as sunflower oil are healthier alternatives.
References:  Mozaffarian, D., Aro, A., & Willett, W. C. (2009). Health effects of trans-fatty acids: experimental and observational evidence. European journal of clinical nutrition, 63, S5-S21.  Przybylski, R., & Aladedunye, F. A. (2012). Formation of Trans fats: during food preparation. Canadian Journal of Dietetic Practice and Research, 73(2), 98-101.  Schwab, U. (2014). 1, Lauritzen L 2, Tholstrup T 2, Haldorssoni T 3, Riserus U 4, Uusitupa M 5, Becker W 6. Effect of the amount and type of dietary fat on cardiometabolic risk factors and risk of developing type 2 diabetes, cardiovascular diseases, and cancer: a systematic review. Food Nutr Res.  Morrison, M. C., Mulder, P., Stavro, P. M., Suárez, M., Arola-Arnal, A., Van Duyvenvoorde, W., … & Kleemann, R. (2015). Replacement of dietary saturated fat by PUFA-rich pumpkin seed oil attenuates non-alcoholic fatty liver disease and atherosclerosis development, with additional health effects of virgin over refined oil. PloS one, 10(9), e0139196.  Khurana S, Venkataraman K, Hollingsworth A, Piche M, Tai TC. Polyphenols: benefits to the cardiovascular system in health and in aging. Nutrients. 2013; 5(10):3779–827. doi: 10.3390/nu5103779 PMID: 24077237  Pellegrini, N., Visioli, F., Buratti, S., & Brighenti, F. (2001). Direct analysis of total antioxidant activity of olive oil and studies on the influence of heating. Journal of Agricultural and Food Chemistry, 49(5), 2532-2538.