This does not tell the whole story. In fact, more and more research indicates this is a flawed recommendation. While it’s true that vegetable oils are generally more neutral in flavor (and more cost-effective for use in large quantity-cooking like deep frying), pure extra virgin olive oil is much more stable than other oils when heated. And it’s significantly healthier (with the exception of avocado oil, which is equally nutritious). Here’s a look at why olive oil should be your go-to cooking oil for all uses.
The Varying Quality and Benefits of Olive Oils
It isn’t a secret that olive oil is good for you, but most people associate olive oil mainly with its heart-healthy monounsaturated fat. Another huge health benefit to olive oil is the antioxidants it contains from the mix of plant polyphenols that are found in the olives. These disease-fighting compounds are what give olive oil its green hue. That said, not all olive oil is created equal. Virgin olive oil, for instance, contains a minimum polyphenol content of 50 mg/kg. But in the European Union (EU), olive oils must contain 250 mg/kg or greater in order to contain an approved health claim related to the oil’s polyphenols. The quality of the oil—including polyphenol content—is dependent first on how the olives are farmed and harvested and then how the olive oil is bottled and stored. Katerina Mountanos, founder of the Greek olive oil company Kosterina, explains that harvesting olives early while they are green, before they ripen—known as “early harvest olive oil”—is an important step to ensuring a high polyphenol content (along with the use of organic farming methods free of pesticides and herbicides). “For a high-quality olive oil, the olives must be milled within four hours of harvesting,” she says. This early harvesting, along with organic farming methods and careful processing and bottling, can all contribute to a polyphenol content as high as 400 mg/kg. Unfortunately, most extra virgin olive oils on the market are nowhere near this count. So what should you look for when buying olive oil? To get an idea of which brands offer the healthiest olive oils, look online for “polyphenol rich” olive oils. Another quick method is to look for olive oil that is not bottled in clear glass. This indicates the producer understands how olive oil should be properly stored (because it degrades with light exposure). Next, check the harvest date found on the bottle and make sure it is within the last year. Lastly, if you have an opportunity to smell or taste the oil before buying it, Mountanos says that a good quality early harvest olive oil will be highly aromatic and complex in flavor. “It should have a peppery finish at the back of your throat, indicating the oil was made from unripe olives high in polyphenols.”
Misconceptions
Common wisdom about cooking with olive oil is that it has a lower smoke point than most other oils. We’re told that heating it past its smoke point creates harmful compounds and will destroy most of what makes olive oil healthy in the first place (i.e., the free-radical fighting polyphenols). But that’s not true, according to recent scientific research—which tells us that high-quality extra virgin olive oil that has not been refined or blended with other oils is, in fact, highly stable when heated. It not only has a high smoke point, but most importantly, it does not break down into harmful compounds like other oils when heated at high temperatures.
The Over-Reliance on Smoke Point
Smoke point is not the end-all-be-all when assessing a cooking oil, says Selina Wang, PhD, a professor in the department of food science and technology and research director of the Olive Center at the University of California, Davis. Rather, she points out, smoke point “is a crude physical measurement of an oil when it starts to have visible smoke….Research in more recent years has shown that smoke point does not correlate well with the changes in the chemical composition of an oil during heating. The chemical changes are much more complex and depend on many variables such as the moisture, acidity, and antioxidant properties of an oil.” Wang references a 2018 study that compared olive oil with other oils during heating. It clearly showed that extra virgin olive oil is the most stable when heated, and produces the least amount of polar compounds (the harmful by-products that come from heating oils). In fact, all other vegetable oils high in polyunsaturated fats were found to produce more polar compounds when heated despite their high smoke points.
The Importance of Preserving Polyphenols
So what about the concern that heating eliminates the health benefits of extra virgin olive oil? Again, scientific research indicates these concerns to be unsubstantiated. First, oils with higher levels of polyphenols produce fewer polar compounds when heated. Wang explains this is because the polyphenols are antioxidants and therefore “protect the oil from breaking down during heating,” making extra virgin olive oil “a good option for frying and cooking.” Secondly, while some polyphenols are more heat sensitive than others and will decrease during heating, research shows that a significant amount of polyphenols still remain in the oil after heating. In fact, some beneficial compounds with important anti-inflammatory and antioxidant benefits in virgin oils stayed completely intact even when heated to over 400℉. Finally, in a 2015 study, researchers even found that vegetables fried or sautéed in olive oil contained higher levels of antioxidants due to the polyphenols that were transferred from the oil into the food.
Why We Got It Wrong
Where did this misinformation come from? Mountanos speculates that one reason is the historical lack of high-quality olive oil readily accessible in the United States. It’s likely that recommendations have been based on olive oil that was refined, mixed with other oils, or not 100 percent extra virgin, and thus would not stand up to heat as well. Wang adds that “some [older] studies were done using heating conditions that would exceed those used in normal food preparation—e.g., frying at 180 for 1.5 hours to 25 hours” and were therefore misleading. Lastly, one of the most significant contributing factors to the olive oil myth is the focus on smoke point alone, which we now know is not necessarily the best indicator of an oil’s ability to withstand heat.
The Key Takeaways
Make sure you are buying true extra virgin olive oil. Look for unrefined 100 percent extra virgin oil, a recent harvest date, and a dark bottle. Organic is ideal, but it does come at a higher cost. Extra virgin olive oil is the most stable oil to cook with and can be heated as high as 400 F (deep frying occurs at 350-375 F). Even when heated past its smoke point, virgin olive oils produce low levels of harmful compounds due to the high antioxidant content in the oil. Polyphenol antioxidants still remain after heating. Starting with an oil extra high in polyphenols (over 250 mg/kg) is recommended so that even more remain after heating.
