High heat can damage cooking oils, causing them to break into cancer-causing free radicals. Is your cooking oil causing cancer?

Is Your Cooking Oil Causing Cancer?

High heat can damage cooking oils, causing them to break into cancer-causing free radicals. Is your cooking oil causing cancer?There are dozens of options on the market these days when it comes to cooking oil. You can choose from canola, olive oil, coconut oil, or go for something more exotic like avocado oil. The choices can seem endless, and we’ve been told that vegetable oils are lower in saturated fats which is good, right? However, most of the oils marketed for cooking simply cannot stand up to cooking temperatures and break down into free-radicals and other dangerous chemicals, which cause cancer as well as premature aging and other disease.  So is your cooking oil causing cancer? Read on to find out.


How Cooking Oils Are Damaged

There are two major ways that cooking oils can break down into toxic chemicals: age and high heat.

Let’s start with age. As with anything in this world, cooking oils degrade over time. Through exposure to heat, light, and oxygen, all oils will eventually become rancid, breaking down into nasty free radicals. This is easy to avoid by following these tips:

  • Use oils by their use-by date; in general oils will last around 6 months (click here for a complete list of oil shelf life)
  • Store oils in sealed containers
  • Store oils in a cool, dark, and dry place. This means you should avoid setting oil by the stove or keeping oil in clear containers (unless the oil will be kept somewhere very dark).

High heat can also damage oils. At high heat, oils form free radicals, similar to an accelerated aging process, and aldehydes (the most common aldehyde is formaldehyde).

Some oils are more susceptible to this damage than others. Unfortunately, traditionally healthier oils which are high in polyunsaturated fats and low in saturated fats are the most susceptible to heat damage. This is because an unsaturated fat is, well, unsaturated. This means that the fat molecule is not carrying the maximum amount of oxygen atoms. Due to these empty molecular spaces, the fat is unstable, and more prone to oxidation (aka loss of electrons). This oxidation is what produces the free radicals and aldehydes.

Related: Good Fats vs. Bad Fats: Why it Matters and How to Tell the Difference

Why Free Radicals and Aldehydes Are Dangerous

So why exactly do we care that overheating an oil creates free radicals and aldehydes? Well for one, free radicals have been linked to a myriad of diseases, such as cancer, arthritis, bronchitis, heart disease, ulcers, and skin aging. In addition, aldehyde has been linked to diseases such as autoimmune diseases, inflammatory diseases, neurological diseases, cardiovascular diseases, and endochronologic diseases.

In both cases, these compounds are created naturally within the body. However, the body has found ways to cope with the volume of these compounds that is generally produced. For example, when free radicals are formed in the body, anti-oxidant agents bind to them and inhibit oxidation. Similarly, aldehyde dehydrogenases in our body protect us from aldehydes. But the body can only do so much to reduce these toxins, so consuming them only serves to tip the delicate balance our bodies have already achieved, which leads to the buildup of these toxins and the diseases mentioned above.


So is YOUR Cooking Oil Causing Cancer?

As I said above, oils that are high in healthy unsaturated fats tend to be the most susceptible to high heat damage, making them unsafe for cooking. So which oils are safe to use? Unfortunately, the answer isn’t black and white, especially if you want to consider your health.

Factors That Affect Cooking Oil Safety

Each oil has a smoke point, or a temperature at which it begins to burn and smoke, and begins releasing toxic degradation products into the air (plus it ruins the flavor of whatever you’re cooking). This can vary depending on the source of the oil as well as how refined it is. In general, more refined oils have higher smoke points. Unfortunately, they also have fewer antioxidants, meaning they oxidize more easily, leading to the second property of oils.

Each oil also has an oxidation stability, which is a measure of how easily it can break down into free radicals and aldehydes when exposed to heat. Personally, I would expect oils with high smoke points to have good oxidation stability, however this is just not the case. For example, palm oil has a smoke point above 450°F, but an oxidation stability of only 10 hours (at 120°C). But coconut oil, which has a smoke point at about 350°F, has an oxidation stability of 33 hours (at 120°C). Check out a chart of smoke point here, and some data on oxidation stability here.

Oxidation stability depends on the temperature you are cooking at. Most oils’ oxidation stability is measured using the Rancimat test, generally performed at 120°C, which is 49°F. You’ll notice that this is not a cooking temperature. To calculate the oxidative stability at your cooking temperature, the rule of thumb is to divide the time in half for each 10°C increase. Below is a chart of common cooking oils detailing the smoke point and oxidative stability for several temperatures.

Oils I Use

Both of these factors must be considered when choosing on oil to cook with, along with the temperature you plan to cook at and how long it will take to cook. Here are the oils I personally use:

  • Ghee (clarified butter) for medium heat sautéed vegetables
  • Refined Coconut Oil for high heat or long term applications
  • Unrefined Coconut Oil for medium heat applications
  • Extra virgin olive oil for low heat only

Of course you can probably use coconut oil for pretty much every cooking application, but knowing when you can use more flavorful (ghee) or higher antioxidant (olive) oils can be useful. 

So is your cooking oil causing cancer? The short answer is, it depends how you’re using it. Any oil with a smoke point below 300°F is probably a bad choice for a cooking oil overall. And as a rule of thumb, oils should NEVER be re-used, because damage from previous cooking is still present and worsens with each use. 

What oils do you use to cook? Any other oils you’d like to see on the chart? Let me know in the comments below!




About Rachel

Rachel is a blogger and Biophysics Lab Manager who lives in Clemson, SC (go tigers!). After studying conventional pharmaceuticals and how they target specific ailments, she applied that knowledge to figuring out how essential oils can work to treat the same ailments, and ended up creating the blog The Essential Girl.

When she’s not blogging or sciencing the shit out of something in the lab, she likes to swing dance and teach group fitness classes.