By Dr. Mercola
You may have wondered about many of the recommendations you see regarding cooking oils, such as what types are healthiest and how they should and should not be used. There’s peanut oil, safflower oil, coconut, avocado, grapeseed and olive oils, and plenty more. So which one’s best?
It’s probably fair to say that most recipes today calling for some type of oil for cooking usually suggest “vegetable” oil or canola oil. But a recent study1 in Australia found that vegetable oils, which are extracted from seeds, are at the bottom of the barrel, so to speak, because of how they behave in two areas:
- Instability when heated
- The production of harmful compounds when heated
Here’s how the study was carried out: 10 of Australia’s most popular cooking oils were heated in different ways, then returned to room temperature before being stored for later chemical analyzation. The oils tested were:
Extra-virgin olive oil (EVOO)
Virgin olive oil
Rice bran oil
The researchers made interesting observations of the oils, especially in light of other studies that have taken place in recent years. In fact, some of the results were surprising and contradictory to other studies. One finding was that EVOO was rated the best cooking oil for both oxidative stability and lack of harmful compounds produced when heated.
But coconut oil, deemed to be the next safest for cooking at high temperatures, failed when levels of naturally occurring antioxidants were compared. Smoke point, by the way, is the temperature at which it exceeds safety by releasing free radicals that react with oxygen to form harmful compounds that can harm your cells and even your DNA, according to the Health Science Academy.2
Avocado oil didn’t rate as high as one might expect, given other studies, such as one noted by the Healthy Home Economist, which notes that avocado oil has a higher smoke point of 480 degrees Fahrenheit (F) for unrefined and 520 degrees Fahrenheit when refined. In fact, Healthy Home Economist states, “No other oil ranks higher including ghee, tallow and lard, making avocado an excellent choice for high heat cooking and frying.”3
However, the Australian study disagrees, as it found that smoke point was actually not useful in gauging a cooking oil’s suitability for heating and, in fact, those with the highest smoke points tended to produce higher levels of harmful compounds after heating. “4
Interesting Conclusions From Australian Study
To that end, each of the top 10 oils used Down Under underwent two types of testing in scientifically accredited laboratories in Australia to determine the oxidative stability of the oils when they’re heated:
- The first gradually heated 8.5 ounces (250 millimeters (ml)) of each oil from 77 degrees F to 464 degrees F, with samples of each being collected at different levels of heat.
- In the second trial, 3 liters (100 ounces) of each oil were heated in a deep fryer for six hours at 356 degrees F.
Please note that when oils are heated, the rate at which they react with oxygen increases and the oil breaks down, a process known as oxidation. As one study explained, the longer an oil resists oxidation, the healthier it is to eat the food the oil has been heated with.5
However, according to the researchers involved in the featured study, contrary to conventional wisdom, a cooking oil’s smoke point is a “very poor marker” of its safety and stability. Typically, the more saturated fat and monounsaturated fat in an oil, the better its oxidative stability. In fact, according to Diet v.s. disease:
“Data from this study showed that coconut oil had the highest oxidative stability. This is due to its extremely high saturated fat content (about 92 percent), which makes it solid at room temperature …”6
“If a high smoke point did accurately represent an oil’s stability at high heat, the seed oils would produce the lowest levels of polar compounds after cooking, not the highest.”7
Peanut oil came in second on the oxidative stability scale, with extra-virgin olive oil, virgin olive oil and olive oil filling the next three slots. Canola oil came in just ahead of avocado oil, with rice bran (allegedly an industrial fat used for cooking at Chipotle8), grapeseed and sunflower oils coming in dead last.
Polar Compounds and Antioxidant Levels of Cooking Oils
Scientists observed the production rate of harmful polar compounds such as lipid peroxides and aldehydes, produced when an oil breaks down in the heating process.9 Both are linked to serious diseases, including neurodegenerative, age-related, carcinogenic and hypertension-associated illnesses.
In the end, the study concluded that EVOO won the most-stable-oil-when-heated competition, followed closely by coconut oil, and EVOO came out on top in terms of harmful polar compounds produced. EVOO had the lowest amount of harmful polar compounds after heating, followed closely by coconut oil. However, the study authors mentioned that:
“The experiments were carried out without food being cooked. While cooking, the water and steam which comes from the food being cooked aids the process of hydrolysis. The absence of food in these trials may have allowed for a greater impact of oil oxidation when compared with other deterioration reactions.”10
Scientists also reported a big difference between virgin and extra virgin olive oils: All three grades contained many more antioxidants compared with the other oils, with EVOO being highest and having 18 times more than canola oil and 700 times more than coconut oil. EVOO, compared to virgin olive oil and the refined version, differs widely.
It’s a far superior choice and contains many more positive attributes due to the way it’s extracted and produced. Diet v.s. disease contends that “The antioxidant content of extra-virgin olive oil was overwhelmingly greater than all the seed oils, avocado oil and coconut oil combined.”11 However, keep in mind that coconut oil does have other beneficial qualities, like being a good source of medium-chain triglycerides (MCTs).
Olive Oil: A Bona Fide Superfood
Olive oil has been used for several applications for thousands of years, including purification and ceremonial rites and symbolic references such as purity and abundance. Olive oil was a popular trade commodity that, when prepared and cooled properly, could be stored for years, according to early Hebrew and Greek manuscripts.
Olive oil has been used for lamp oil and topically to soothe dry skin. It’s still drizzled on raw vegetables, i.e., salads, and breads with cheese and herbs, such as bruschetta. However, using it for frying was not customary among early cultures. Faye Levy, author of “1,000 Jewish Recipes” states:
“The French chefs I studied with in Paris preferred delicate olive oil and reserved it mainly as a ‘finishing’ oil for drizzling over cooked dishes at the last minute … If you have a really good olive oil, it’s best to use it in a dish where the oil’s taste is noticeable, such as a dip or salad …
Even a modest amount of a fruity, somewhat pungent olive oil will provide plenty of flavor. Because the flavor of extra-virgin olive oil is finest when the oil is heated gently or not at all, it’s a good idea to reserve your best bottles of olive oil for adding to dishes at the last moment.”12
Unfortunately, producing extra-virgin olive oil has become a big business, which has led to fraud the world over. Even olive oils labeled “extra virgin” may have been tampered with and adulterated by being diluted with inferior oils, such as some of the seed oils previously mentioned. Taste and smell are two of the best ways to determine authenticity.
Why Olive Oil Is So Good for You
Olive Central, a “portal for the South African olive industry,” observes that extra-virgin olive oil has a number of health benefits and lists five main reasons why it’s a bona fide superfood:
- Oleocanthal — This phenolic compound has reportedly shown several ways in which it reduces diseases affecting joints, neurodegeneration and certain cancers. It may inhibit the COX1 and COX2 enzymes that cause inflammation and prevent Alzheimer’s disease by helping clear beta-amyloid plaques from your brain.13
- Antioxidants — These can help prevent cell damage caused by oxidants, protect your body from damage caused by free radicals that can cause serious diseases, including cancer, and reduce your risk of heart disease.
- Monounsaturated fatty acids — These fatty acids are “good” fats found to protect against disease by increasing your cell membranes’ elasticity, which reduces your risk of heart disease, diabetes, atherosclerosis and colon cancer, and may benefit insulin levels.14
- Vitamin K — A fat-soluble vitamin recognized for its role in blood clotting, this vitamin helps build strong bones and may help prevent heart disease. One tablespoon of EVOO contains about 10 percent of the reference daily intake (RDI) recommended for adults.
- Vitamin E — Vitamin E, aka tocopherol, is a fat-soluble vitamin that plays an important role in protecting against skin and eye problems, cancer and diabetes, as well as neurological diseases like Alzheimer’s. Often included in skin creams, it helps promote healing and reduces scarring.15
Cooking Oil: What to Use, What to Avoid
When it comes to cooking foods with oil, one of the things to watch for is oils that are hydrogenated or interesterified (a fat where the triglyceride molecule is engineered to change the melting point of the oil). One thing untested in the Australian study was something Americans use often: organic, grass fed butter, which is among the best fats to cook with. Ghee, another delicious alternative, has been used for cooking for eons and is another good choice.
Perhaps the information unmasking margarine as an artery-clogging substitute is old news, but just in case, avoid margarine along with refined cooking oils and vegetable oil, and avoid vegetable shortening, as well. Polyunsaturated fats may be the worst, as the omega-6 fatty acids are more prone to damage — one reason to stay away from corn oils, soybean oil, safflower, cottonseed oil and canola oils, too.
Coconut oil has much more going for it than the Australian study revealed. Fifty percent of its fat content is lauric acid, which your body converts into monolaurin, which contains powerful antiviral, antibacterial and antiparasitical properties.
Multiple studies point to coconut oil and avocado oil as far superior to olive oil for heating food due to the smoke point, but some of the most prominent entities people turn to for information regarding their health have not yet gotten the memo regarding healthy fats; some may in fact be ignoring the newest studies.16
It’s worth mentioning, too, that the Australian study was carried out by researchers with Modern Olives Laboratory Services, which provides services for the olive oil industry. While there’s no doubt that olive oil is good for your health, its suitability as a cooking oil deserves further study.