Most people never really consider what oil they use for cooking. Even I can’t be bothered to think about it. With so many types of cooking oil to choose from, what’s the point? Is there really a difference?
The general belief is that saturated fats (such as lard and butter) are bad for us while vegetable/seed oils such as corn oil and sunflower oil are the healthiest cooking oils for us. Maybe that’s what we’ve been taught or maybe that’s just what our mothers told us.
However, a recent Australian study can completely change the advice on how we choose our cooking oil.
The study at-a-glance
The study tested 10 of the most popular cooking oils:
Extra virgin olive oil (EVOO)
Virgin olive oil
Rice bran oil
Canola oil (also called rapeseed oil)
Each oil was tested in two different heating trails before being cooled at room temperature and analyzed.
The first test was to gradually heat 250mL of each oil in a pan fryer from 25ºC to 240ºC while collecting samples at different heat intervals.
3L of each oil was heated in a deep fryer at 180ºC (recommended temperature for deep frying) for 6 hours, collecting samples at different time intervals.
The study concluded that extra-virgin olive oil (EVOO) — not coconut, sunflower, or avocado oil — was best for cooking, as testing gave it the highest overall ranking for oxidative stability, amount of antioxidants and lack of harmful compounds produced when heated.
What criteria was used to determine the healthiest cooking oil?
Oxidative Stability (Higher=Better)
Most researches are based around how oils behave when heated. 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).
What’s bad about the oxidation anyway?
It’s the end products of oxidation we’re worried about. Oxidation is a chemical reaction that alters the molecular structure of the oils and creates new compounds which could be harmful to our health.
The quality of an oil to resist oxidation before and after heated is called oxidative stability.
A study showed that the longer an oil resists oxidation (higher oxidative stability), the healthier and better it is for cooking. (1)
Here’s a graph representing the oxidative stability of each oil before heating trials:
We can see that coconut oil had the highest oxidative stability, followed closely by peanut oil and extra virgin olive oil.
This is mainly due to its high saturated fat content (92%) . The olive oils’ oxidative stability, however, comes from high amounts of antioxidants already present in the first place.
The seed oils? Not very promising.
Harmful Compounds Produced (Lower=Better)
Of course, the most important factor is “Which oils produced the most harmful products when heated?”
Here’s a graph that illustrates the number of polar compounds that formed in each oil:
It’s clear that extra virgin olive oil and coconut oil formed the fewest harmful compounds.
On the other hand, it is worrying that the canola oil produced the highest amounts of harmful compounds when heated reaching a value of 27.5% – considering it’s one of the most commonly used cooking oils.
Antioxidant Content (Higher=Better)
Scientists reported that extra virgin olive oil had the highest levels of antioxidants, with 18 times more than canola oil and 700 times more than coconut oil. An antioxidant, by the way, is as the name suggests – a substance that inhibits oxidation.
“However, keep in mind that coconut oil does have other beneficial qualities, like being a good source of medium-chain triglycerides (MCTs).” according to Dr. Mercola.
"What about the smoking point?"
The smoke point has always been the conventional “marker” for an oil’s safety and stability.
Smoke point, by the way, refers to the temperature at which an oil starts to burn and smoke and becomes unsafe. When oils start smoking, it releases free radicals which react with oxygen to form harmful compounds.
“That’s useful. All I have to do is use the oils with the highest smoke points. As long as the oil I use doesn’t start smoking easily, I’m safe.” It makes sense, right? That’s why most people use vegetable oils because of their high smoke point. You’ll find it emphasized in most articles and it became the standard.
But, the recent study disagrees, as it found that smoke point is actually not useful and is a “poor marker” in gauging a cooking oil’s suitability for heating.
As we can see from the graphs, those with the highest smoke points (the vegetable oils/seed oils) tended to produce higher levels of harmful compounds after heating. “If a high smoke point did accurately represent an oil’s stability at high heat, the seed oils would have produced the lowest levels of polar compounds after cooking, not the highest.”
Extra-virgin olive oil is the overall winner as it was the most resistant to heat, had the highest antioxidant content, and is more stable and more versatile to use(think of salads).
The runner-ups are coconut oil followed by the other virgin oils. Seed oils(vegetable) on the other hand, are a poor choice due to the fact that they produced the most harmful compounds when heated.