The Standard American diet, full of fried foods, poses a public health crisis because of the level of unhealthy fats and oxidants that are present in the oils that the foods are cooked in. Denatured, refined cooking oils oxidize at various temperatures. After they oxidize, the refined oils become inflammatory and release cancer-causing byproducts (such as aldehydes) into the food. These inflammatory byproducts weaken the body’s ability to fight infections and fuel the chronic diseases and underlying comorbidities that are the precursor to severe disease outcomes.
Vegetable oils and the oxidation process
Most vegetable oils consist of polyunsaturated and monounsaturated fats that are MORE prone to oxidation than saturated animal fats. Martin Grootveld from De Montfort University in the UK says oils can be measured by “calculating the stability of heated oil over time.” Grootveld specializes in bio-analytical chemistry and chemical pathology. He said the oxidation process determines how quickly an oil produces potentially harmful compounds.
In order to measure an oil’s stability, it is heated to 230 degrees Fahrenheit. This is typically when an oil begins to form oxidants. As the oxidants form, they dissolve into water-filled conductivity cells, changing the conductivity of the water. When the water’s conductivity is significantly altered, the test determines how great the oxidation is. An oil with a longer stability time is an oil that can withstand higher cooking temperatures without producing significant amounts of oxidants.
Oxidative stability of common cooking oils and fats
The least stable cooking oils are sunflower, soybean, and canola oil. Sunflower and soybean oils contain high polyunsaturated fatty acid content (between 61% and 69%) and are therefore prone to quick oxidation at high temperatures. Canola oil is composed of 60% monounsaturated fatty acids and is a little more stable than the aforementioned. The oxidative stability of canola oil is around six to eight hours. At temperatures exceeding 365 degrees Fahrenheit, the oil produces oxidants within 60 to 90 minutes.
Oils that possess higher oleic acid content have a more stable profile of monounsaturated fatty acids and therefore have a higher oxidative stability. Two cooking oils that are more stable include extra virgin olive oil and avocado oil. Olive oil is comprised of about 60% monounsaturated fatty acids and avocado is around 80% - giving both a higher heat resistance than vegetable oil and canola oil. In fact, the oxidative stability of olive oil is four times greater than canola. Its oxidation score is 32 hours at 230 degrees Fahrenheit. However, higher temperatures (365 degrees Fahrenheit) cause both olive and avocado oil to oxidize similar to canola oil. The best olive oil is unrefined extra virgin olive oil because the oil still contains important antioxidants that block oxidant formation and proliferation.
Palm oil, which is around 50% saturated fat, has great stability at high heat, too. Due to its high content of vitamin E and beta-carotene, red palm oil is able to keep many oxidants from forming during the cooking process. It has an oxidation stability score of about 16 hours. In comparison, avocado’s score is 10 hours at 230 degrees Fahrenheit.
With a saturated fat content greater than 80%, both coconut and palm kernel oil are highly resistant to oxidation. However, these oils are comprised of medium-chain fatty acids that have a lower melting and smoke point than all the other saturated fats. Still, coconut oil retains an oxidative stability of 51 hours at 230 degrees Fahrenheit, making it one of the most healthy oils to consume in terms of oxidants.
Tallow, butter, and ghee are the only other fats that have a more prolific oxidative stability. Tallow, which is the fat taken from beef or lamb, contains more than 50% long-chain saturated fatty acids. This makes tallow very stable at high heat, giving it an oxidative stability score of 69 hours. Both butter and ghee are heat stable for the first 20 hours, before they begin to slowly oxidize.
When cooking, it’s important to use a clean, unrefined cooking oil or fat that does not readily break down into oxidants during high heat. This is important for protecting the cells from inflammation and oxidative damage.
Sources include:
Alfalaval.com [PDF]
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