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Why We Avoid Cooking With Extra Virgin Olive Oil

Even though we strongly recommend the inclusion of extra-virgin olive oil (EVOO) in most meal plans—and average 2 tablespoons per day in our 7-Day Menu—we do not cook with this plant oil and we do not believe that cooking with EVOO is the best way for you to incorporate it into your healthiest way of eating. However, we also recognize that there are two basic ways of thinking about the use of EVOO in cooking, and we have created this article to describe both of these perspectives and to provide you with enough research information for making a personal decision about the use of EVOO in your healthiest way of eating.

Perspective 1 - Placing the focus on fat composition

From a research perspective, EVOO is unusual in its fat composition. And not only is its fat composition unusual, but it also lends itself to heating. A little bit of chemistry here can be helpful in understanding this aspect of EVOO.

The "heat friendly" fat composition of EVOO starts with its unusually high monounsaturated fat content. EVOO is approximately 73% monounsaturated, with oleic acid—an omega-9 fatty acid—serving as its key monounsaturated fat. In chemical terms, monounsaturated fats are fats with only one "unsaturation spot" where oxygen damage is especially likely. (The "mono" in "monounsaturated" lets us know that there is only one spot.) By contrast, polyunsaturated fats always have two or more unsaturation spots, and more places where oxygen damage is especially likely. When oxygen interacts with these spots, the chemical process is called oxidation, and because these substances are fats, the chemical process in these situations is called lipid peroxidation.

When cooking oils are heated, the heat brings more energy into all chemical reactions, and it also speeds up those reactions—including lipid peroxidation. This impact of heat is true for any cooking oil—sunflower, safflower, corn, soy, or EVOO. But unrefined oils that are highly polyunsaturated, like unrefined sunflower or safflower oil, undergo more lipid peroxidation when heated that monounsaturated oils like EVOO because there are more opportunities for oxygen to interact with these unrefined polyunsaturated oils. When researchers compared EVOO to polyunsaturated oils, they often describe it as having a good amount of heat stability and "thermal resistance." In simple everyday terms, good heat stability and thermal resistance mean generally appropriate for use in cooking.

In addition to its high monounsaturated fat content, EVOO has also been shown to contain very low amounts of free fatty acids in comparison to many other oils. (Free fatty acids are simply isolated building blocks of fat that have not been linked together to form a larger and more complicated fat molecule.) Because free fatty acids are more available in chemical reactions (including oxidation), too many free fatty acids means a higher risk of oxidation. And by contrast, a very low level of free fatty acids (as is the case with EVOO) means a lower oxidation risk.

In summary: from the perspective of its fat composition, EVOO is a good candidate for use in cooking, and it is widely used in cooking in many cuisines through the world.

Perspective 2 - Placing the focus on phenols and polyphenols

No less unique than the fat composition of EVOO is its phytonutrient composition, and especially its rich and diverse supply of phenols and polyphenols. In our food profile for EVOO , you can find more specifics about these phytonutrients and their role in health. While EVOO is fairly stable to heat in terms of its fat composition, it is quite unstable to heat in terms of its phenol and polyphenol composition. Recent studies show that phenols and polyphenols in EVOO—for example, hydroxytyrosol or luteolin —are not stable to heat and degrade relatively quickly. For example, when heated in a container over a flame for only 5 minutes at a temperature of 461°F/188°C, one study has shown 50% loss of hydroxytyrosol and 69% loss of luteolin. In this same study, similar trends were found for oven baking and microwave cooking of EVOO.

Comparing the Two Perspectives

Because many people have chosen to cook with EVOO based on its heat-friendly fat composition, researchers have looked at some of the particulars of the cooking process and found some nutritional benefits from cooking with EVOO. For example, the cooking of chopped tomatoes together with EVOO has been shown to help solubilize carotenoids in the tomato and make them more bioavailable. This type of research finding on the use of EVOO in cooking is one of the factors that people consider when deciding to cook with this oil.

At WHFoods, we understand why many people may choose to go ahead with the use of EVOO in cooking, for all of the research-based reasons described above. However, in development of our recipes and meal plans, we deliberately decided to give more weight to the second cooking perspective that focuses on the unique phenols and polyphenols present in EVOO. The health benefits from these EVOO phytonutrients seem too important to forego. In addition, whether we are talking about EVOO or any other food, all of our recipe and meal plan decisions are designed to minimize nutrient loss—including phytonutrient loss. In this case, the best way to minimize nutrient loss was to avoid the use of EVOO in cooking.

General Questions Involving Smoke Point

In a good number of internet discussions, you will find arguments about the use or non-use of EVOO in cooking that focus on the issue of smoke point. Not only do we believe that smoke point is not a helpful issue to focus on when trying to decide whether or not to cook with EVOO, we believe it is also a confusing issue in and of itself. So we would like to provide you with some research-based details in this area.

All cooking oils have some smoke point. Typically, this smoke point falls between 200-500°F (93-260°C). In general, the smoke point of cooking oils falls into the upper half of this range.

Smoke point is not defined as the moment when a heated oil first begins to smoke. It's defined as the moment when a heated oil begins to smoke continuously. The moment when an oil starts to smoke continuously corresponds to the moment in time when its fat molecules start to break down at a much faster rate. (In chemical terms, the breakdown of triacylglocerols, or TAGs, into glycerol and free fatty acids starts to proceed at a much more rapid rate beginning at smoke point.)

As the breakdown of fat molecules speeds up, additional problematic by-products are formed. For example, once smoke point has been exceeded, more glycerol molecules get converted into acrolein, a substance that can bring along with it unwanted health risks if we end up having overexposure to it. At WHFoods, we are not aware of any studies that recommend going beyond an oil's smoke point, and we recommend staying below smoke point as a general cooking practice if oils are used during cooking.

What actually causes a cooking oil to smoke? The direct answer to this question is "numerous factors." And this is one place where you will need to exercise some caution in reading many website reports. For example, you will find some website articles focusing on the amount of saturated fatty acids (SFA), monounsaturated fatty acids (MUFA), and polyunsaturated fatty acids (PUFA) in an oil as the key factor when determining its smoke point. Research studies do not support this point of view. The balance between SFA-MUFA-PUFA definitely has an impact on smoke point, but a more important contributing factor is the length of the fatty acids themselves. Fatty acid size is measured by "chain length," which is shorthand for the number of carbon atoms linked together in a chain.

Let's take the example of EVOO and coconut oil. Even though EVOO is an oil with relatively low PUFA content, it nevertheless contains more PUFA content than coconut oil. Based on this characteristic, you might expect it to have a lower smoke point due to a greater risk of PUFA oxidation. However, coconut oil actually has the lower smoke point than EVOO—347°F (175°C) versus 383°F (195°C). One important reason involves the lack of short chain fatty acids in EVOO, and the unusually large number of short chain fatty acids in coconut oil. So as you can see, it can be a mistake to jump to conclusions about oils and their smoke points.

Several other issues involving smoke seem important to mention here. First, all smoke is not the same. Smoke from cooking oil is not the same as smoke from cigarettes or smoke from a car exhaust. All smoke can contain solids and liquids and gases, and all smoke reflects the occurrence of "incomplete combustion"—meaning that there is not enough oxygen immediately available to completely burn the substance that is giving off smoke. When EVOO is heated above smoke point, aldehydes from the heated oil including alkanals, alkenals, and alkadienals get released and become part of the cooking oil smoke. Even though smoke from a burning cigarette might look similar to smoke from overheated EVOO, its composition is in fact very different. For example, in cigarette smoke, you are likely to find nitrogen-related radicals, including nitric oxide and its close derivatives.

Comparing the Smoke Point of EVOO with Other Oils

One recent research study in this area lists the following four cooking oils and their smoke points.

  • Coconut oil: 347—F (175—C)
  • EVOO: 383—F (195—C)
  • Safflower oil: 414—F (212—C)
  • Canola oil: 460—F (238—C)

You will notice that EVOO falls into a "middle" range in terms of smoke point in this study, and as a general rule, we believe that "middle range" is a good way of describing the smoke point of EVOO in comparison to other cooking oils. However, the information above only shows the relationship between smoke point and oils from different plants. Missing from this list, however, is a second type of information that is always just as important—and sometimes more important—than the plant from which the oil was obtained. This missing information involves steps that were taken during the processing of the oil.

While all oils have been processed in some way, many are also processed to make them more "refined." Refining is a process that typically involves removal of numerous substances (including phytonutrients) from the oil. For example, free fatty acids, gums, and color pigments are frequently reduced during refinement. In the case of olive oil, refining is sometimes used to lower the acidity of the oil and make it palatable for consumption from a taste standpoint. Refinement of oils also raises their smoke points and frees them up for a longer shelf life and for use with a wider range of cooking heats. It is often possible to nearly double the smoke point of an oil through the refining process. A canola oil that started out unrefined with a smoke point of 225°F (107°C) might end up with a smoke point of 400°-460°C after full refinement. Similarly, sunflower and safflower oils that stated out with smoke points of 225°F (107°C) might have their smoke points raised to 450°F (232°C) after being refined.

In the smoke point values presented above at the beginning of this section, we suspect that the coconut oil and EVOO were less refined than the safflower oil and canola oil, such that the much higher smoke points of the safflower oil and canola oil were not due to the plants from which these oils were obtained, but to the way that they were processed. However, since the authors of the study from which we obtained this list did not specific the degree to which any of the four plant oils had been refined, we cannot say for certain what factors contributed to these different smoke points. But what we can say is that the plant source of an oil may not tell you enough about the smoke point of an oil, and that processing may play a much larger role in controlling when you start to see continuous production of smoke when heating an oil.

Nutrient Loss Can Take Place Even Below Smoke Point

In addition to the reasons described above for avoiding smoke point as your primary determining factor when deciding whether to cook with EVOO, we want to point out yet another reason for thinking about other factors rather than smoke point. That factor is quite simple: even if the EVOO cooking temperature stays below smoke point, nutrient richness can be decreased. For example, we've seen one study that showed loss of vitamin E in olive oil after one minute of microwaving at 1000W (watts). This loss of vitamin E occurred long before smoke point was reached. We have also seen a study that showed a 14% reduction in oleuropein—a key anti-inflammatory phytonutrient in EVOO—after one hour of heating at 176°F (80°C). (And once again, you can see that this temperature fell far below the smoke point for EVOO.) In addition, numerous studies show 5-15% loss of various phytonutrients following the use of EVOO in cooking, even when the cooking temperature remains below smoke point.

The fact that nutrients can be lost far below smoke point is also well-illustrated by the example of chlorophyll. This antioxidant pigment is quite unstable to heat, and you do not need to get anywhere near the smoke point temperature of EVOO to start seeing loss of chlorophyll. In fact, at 140°F (60°C), researchers have documented decoloration of virgin olive oil (VOO) due to measurable loss of chlorophyll. Of course, you can watch this process happening before your very eyes since many olive oils have their own unique visibly green hues, and these hues can begin to change in a period of several minutes at temperatures as low as the 140°F (60°C) mark listed above. What we want to emphasize here is not the dangers of the smoke since researchers unanimously agree that once you heat EVOO above its smoke point and start to see continuous release of smoke, you have in fact overheated it from a health standpoint. Instead, we want to emphasize the known nutrient changes that can take place below smoke point, including changes to chlorophyll, phenols, and polyphenols.

WHFoods Recommendations

As described earlier in this Q & A, we understand why many people may choose to go ahead with the use of EVOO in cooking. There are some good research-based reasons for doing so, including the relatively heat stable fat composition of EVOO, and the fact that nutrient bioavailability in other foods—like carotenoids in tomatoes—may be improved through the use of EVOO in cooking. However, all of our recipes and meal plans at WHFoods are based on the principle of minimizing nutrient loss, and due to the rich phenol and polyphenol content of EVOO that are instable to heat, there is no way to uphold that principle unless cooking with EVOO is avoided. We recommend avoidance of EVOO in cooking for precisely this reason: we cannot see how to preserve the maximum phytonutrient content in EVOO unless cooking heats are avoided.

For some easy to prepare and delicious recipes that include EVOO but avoid cooking heats, just use our Recipe Assistant and select "olive oil" from the "Foods to Include" menu.

References

  • Allouche Y, Jimenez A, Gaforio JJ, Uceda M, Beltran G. How heating affects extra virgin olive oil quality indexes and chemical composition. J Agric Food Chem 2007;55:9646-9654.
  • Aparicio-Ruiz R and Gandul-Rojas B. (2014). Decoloration kinetics of chlorophylls and carotenoids in virgin olive oil by autoxidation. Food Research International 65: 199—206.
  • Attya M, Benabdelkamel H, Perri E, et al. Effects of conventional heating on the stability of major olive oil phenolic compounds by tandem mass spectrometry and isotope dilution assay. Molecules. 2010 Dec 1;15(12):8734-46.
  • Bagoria R, Arora A, and Kumar M. Thermal decomposition behavior of edible oils in different atmospheres. Archives of Applied Science Research, 2012, 4 (6):2382-2390.
  • Bastida S and Sanchez-Muniz FJ. Chapter 21 - Frying: A Cultural Way of Cooking in the Mediterranean Diet. The Mediterranean Diet, 2015, pages 217-234.
  • Casal S, Malheiro R, Sendas A et al. Olive oil stability under deep-frying conditions. Food Chem Toxicol. 2010 Oct;48(10):2972-9. Epub 2010 Aug 3. 2010.
  • Cicerale S, Conlan XA, Barnett NW, et al. Influence of heat on biological activity and concentration of oleocanthal--a natural anti-inflammatory agent in virgin olive oil. J Agric Food Chem 2009;57:1326-30.
  • Dairi T, Galeano-Diaz MI, Acedo-Valenzuela MP, et al. Monitoring oxidative stability and phenolic compounds composition of myrtle-enriched extra virgin olive during heating treatment by flame, oven and microwave using reversed phase dispersive liquid—liquid microextraction (RP-DLLME)-HPLC-DAD-FLD method. Industrial Crops and Products, Volume 65, March 2015, pages 303-314.
  • Echevarria B, Encarnacion G, Manzanos NJ, et al. The influence of frying technique, cooking oil and fish species on the changes occurring in fish lipids and oil during shallow-frying, studied by 1H NMR. Food Research International, Volume 84, June 2016, pages 150-159.
  • Katragadda HR, Fullana A, Sidhu S, et al. Emissions of volatile aldehydes from heated cooking oils. Food Chemistry, Volume 120, Issue 1, 1 May 2010, Pages 59-65.
  • Moreno DA, López-Berenguer C, García-Viguera C. Effects of stir-fry cooking with different edible oils on the phytochemical composition of broccoli. J Food Sci. 2007 Jan;72(1):S064-8. 2007. PMID:17995900.
  • Santos CSP, Cruz R, Cunha SC, et al. Effect of cooking on olive oil quality attributes. Food Research International, Volume 54, Issue 2, December 2013, pages 2016-2024.
  • Vallverdu-Queralt A, Reguiero J, de Alvarenga JR, et al. Home Cooking and Phenolics: Effect of Thermal Treatment and Addition of Extra Virgin Olive Oil on the Phenolic Profile of Tomato. Agric. Food Chem. 2014, 62: 3314-3320.

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