Everyone has their own opinion as to which oils are good and bad, but very few seem to want to back it up with any real evidence. This guide is intended to be the definite guide to cooking oils, and by the end you should know:
- The different types of fats that oils are made of
- What lipid peroxidation is and why it matters
- Why the smoke point isn’t the only important property of oils
- Which oils are and are not Paleo
- Which oils are the best to cook with
The 2 Types of Fat
All oils are made of fats (a type of lipid) that can be divided into saturated and unsaturated fats.
All fats are long chains of carbon molecules with a “COOH” group on the end. The simplest type of fat is a saturated fat, shown below:
The second main type of fats are unsaturated fats. This type can further be divided into 3 different types of unsaturated fats.
“Mono” is Greek for 1, so it shouldn’t be a surprise that monounsaturated fats have one double bond, where the carbons aren’t saturated. Take a look at the basic structure:
Polyunsaturated Fatty Acids
If “poly” is Greek for multiple, can you guess what polyunsaturated fats look like? That’s right, they have more than one double bond because the carbons are not saturated.
Trans Unsaturated Fatty Acids
Many people don’t know that trans fats are actually unsaturated. They are named because of an important feature of the double bond.
The only difference between trans and monounsaturated fats is on the double bond, where the hydrogen bonds are on opposite sides. This is called a trans isomerism (hence the name “trans” fat), while hydrogens on the same side are called a cis isomerism.
Trans fats are pretty safe to declare as bad fats. You do not need any trans fats to be healthy, and should try to avoid them when possible. That being said, there is a difference between natural and man-made trans fats. While the evidence is not conclusive, it appears that natural trans fats, although rare, may not be dangerous to your health.
The trans fats that you find in products like margarine and certain oils are highly dangerous. They raise your risk for cardiovascular heart disease, likely because they cause significant inflammation that triggers your LDL (‘bad’ cholesterol) to rise, and your HDL (‘good’ cholesterol) to lower. Trans fats are created as a byproduct of hydrogenation.
Bottom line: Be wary of any oils with trans fats in them (often labelled “hydrogenated”), like margarine.
The Stability of Oils
I’ve already mentioned fat stability a few times, and now we’re going to address why it’s so important. When oils are reactive, they have a nasty tendency to form dangerous compounds that can have a negative effect on your health. Just because an oil is ‘healthy’, doesn’t mean that it’s good for you in all situations.
Factor 1: Smoke Point of Oil? (and Why You Should Care)
The smoke point is a very important property of oils, but often a misunderstood one. Let’s clear up any confusion.
First of all, what is the smoke point? It’s the temperature at which smoke starts to form from the oil. The big deal is that the compounds present in this smoke are highly dangerous.
The Dangers of Acrolein and Smoke Compound Formation
When an oil reaches its smoke point, it can break down and any free glycerol groups can be converted into acrolein. Acrolein is one of the chemicals in cigarette smoke and is a carcinogen (cancer-causing compound). There’s been multiple studies that have shown that cooking oil fumes can cause cancer if you breathe them in, specifically from the fumes of soybean and rapeseed oils.
Below is a graph of smoke points for common oils. Note that different brands will have variations in their smoke points, so these should be used as general guidelines only.
Also remember that the oil itself has to reach the smoke point temperature to produce smoke, which can take a while depending on the temperature of the stove/oven.
Factor #2: Oxidative Stability
When most people offer their opinions on cooking with fats, they generally speak solely about smoke points. And while it’s definitely a major factor, the most important factor is oxidative stability.
Oxidative stability is a term that describes how resistant a fat is to becoming oxidized. In biology terms, this means how resistant a molecule is to losing a hydrogen atom. When a fat molecule loses a hydrogen atom, it turns into a free radical, which is an unpaired electron. Free radicals are highly reactive and can cause some big problems.
Many types of lipid peroxides and free radicals can be formed depending on the present compounds while cooking. This reaction cycle can happen fast enough and violently enough to damage the DNA of cells. This can lead to a wide variety of diseases, accelerated aging, and cancers.
One interesting note to make is that antioxidants can neutralize a significant portion of free radicals before they have a chance to do any real damage. This is why the antioxidants that a lot of unrefined oils have are important (we’ll get into specifics laters).
How is Oxidation Stability Determined
When an oil begins to become unstable, and all these undesirable reactions start happening, it’s said to have become rancid. Rancidification can be accelerated by heat and exposure to ultraviolet light. Ultimately, most rancidification is caused by oxidation, although hydrolysis is another possible pathway that sometimes occurs.
There’s a few ways oxidation stability can be determined, though it is usually done with the Rancimat method. Basically, air is pumped through a sample of the substance (oil) at a constant temperature, and the temperature is measured over time. Rancidification is reached when conductivity starts to dramatically increase.
Below is a table of induction times (how many hours it took until rancidification began) for different oils. Note that tests were unfortunately run at different temperatures (otherwise some would have taken an extremely long time). I’ve included an adjusted induction time based on the rule of thumb that every 10oC causes a 2-fold change in induction time. Also, I’ve taken the average induction time from the range in the data.
Let’s compare the induction time at 120oC with the smoke points from the last section. But before we do that, let me ask you a question – would you expect an oil with a high smoke point to also have a high induction time?
Once you answer that, take a look at the following plot:
But the graph tells a much different story.
Coconut oil, which has a medium level smoke point, takes pretty much forever to go rancid. This explains why coconut has an extremely long shelf life, but you still wouldn’t want to use it to cook beyond reasonable temperatures.
While palm oil might not smoke easily, but can go rancid fairly quickly. What that means, in a practical sense, is that we can’t justify the stability of a type of oil based on just one property.
Factor #3: Storage and Other Factors
Up until now we’ve been dealing with lab data in ideal conditions. That’s all well and good, but there are some really important considerations you need to make in real life.
The smoke point and rancidity of can be affected by a few different factors:
- Re-using oil: If an oil has already been cooked with, it’s smoke point will be lowered
Exposure to oxygen: More exposure to oxygen increases the rate of oxidation (rate of turning rancid). Not a bad idea to cover that butter
- Temperature: As we’ve seen, higher temperatures increase the rate of oxidation, even if it’s below the smoke point
- Exposure to light: Ultraviolet light waves can accelerate oxidation. Note that light can penetrate transparent containers.
- Rancidity: Since rancidity can damage/consume antioxidants, rancidity may further lower the smoke point. While it makes sense at a glance, and some have claimed this, I could not find a credible source as of now.
Summing Up Oil Stability
The biggest takeaway from all of this is that you shouldn’t obsess over numbers you see published on the internet. Understand what the smoke point and how oils are oxidized (go rancid).
There’s going to be significant variations based on how long you’ve had the oil, how it’s been stored, what brand it is, and so on. Make the best decision possible and take precautions when you can.
Ideally, store oils in dark containers in dark, cold areas (possibly the fridge) in airtight containers. Oils can go rancid over a period of time (months-years depending on the oil), so don’t buy a huge container of oil if you don’t use it frequently.
Refined Oil vs Unrefined Oil
As you’ve seen, oils can be refined or unrefined. You may have also noticed that refined oils have much higher smoke points than unrefined oils. But remember, your decision shouldn’t be based on smoke point alone. Refined oils are often much more susceptible to rancidity, and also contain very little (if any) antioxidants that can help prevent free radical formation during cooking – even at low heats.
How Unrefined Oils Are Made
Unrefined oil simply means that the oil is squeezed out of the flesh, seed, or skin. Take olive oil for example. The olives are crushed and then fed into a machine where they are pulverised to release oil that is then collected. If you see “unfiltered” on a bottle, that means that there may be small solid remnants in the actual oil.
Note that even unrefined oils can be exposed to heat, even though that they are typically labelled as “cold pressed”. When extracted via an expeller (pictured below), the high pressures can create temperatures up to 50 degrees Celcius. Temperatures in this range won’t cause much (if any) damage.
Unrefined oils keep their tastes and smells to varying degrees, as well as all their vitamins, minerals, and antioxidants. Note that it should be a pleasant, or at least expected taste, unlike rancid oil.
How Refined Oils Are Made
Refined oil may go through a similar extraction process as unrefined oil, but often a solvent like hexane is used in order to maximize oil extraction. Refined oil then goes through a few major steps that affects the quality and properties of the oil:
Bleaching involves mixing in a powdered bleaching agent, which binds to pigments, metals, phosphatides and oxidation products (if there are any). The powder is then removed from the oil with a filter.
Deodorization is probably the more evil of the two main steps. Since the oil still smells after all the other steps, this final step is needed to achieve the desired properties. During deodorization, the oil is heated to a high temperature and pretty much any remaining components other than fat are distilled off (including antioxidants). It typically occurs at 175-205 degrees Celsius in European production, but up to 235-250oC in the United States.
Summarizing refined oils: The refinement process leaves edible oils devoid of the majority of their natural nutrients, and damaged due to exposure at high heats. This leaves them with a bland, neutral color and taste, as well as a higher smoke point.
Due to not possessing high levels of antioxidants, they should be avoided during long cooking processes, as free radicals will easily form.
Now that you are an expert on all things oil, let’s break down the individual most popular cooking oils.
Almond oil consists mainly of monounsaturated fats, but also has a fairly high percentage of omega-6 fats (~17%). While polyunsaturated fats typically oxidize easily, antioxidants can prevent free rancidity. Almond oil has a ton of vitamin E, which means that it is probably fine to use for cooking, but no studies have been done to verify this.
From a nutrition standpoint, you don’t want to consume too many omega-6 fats. While a small amount is necessary, a large amount is inflammatory.
Recommendation: While it’s not the best oil, it’s Paleo-friendly and is likely safe to use for cooking at any low to medium temperature.
Avocado oil shares a similar fat profile as olive oil. Avocado oil is mostly monounsaturated, but has a bit less polyunsaturated fats in favor of saturated fat, which makes it a little better for cooking.
While the high amount of polyunsaturated fats might lead you to suspect that avocado oil will also be prone to oxidation in heat, this study shows that avocado performs similar to olive oil under heat. The high amount of vitamin E is highly effective in preventing antioxidation.
Bottom line: Avocado is a good oil to cook with at any temperature under its smoke point. Unrefined avocado oil has a fairly high smoke point of 195 degrees Celsius.
Butter is an interesting cooking fat, even though it’s not typically referred to as an ‘oil’. It has a solid nutritional profile, with a good amount of vitamin A and D. It’s mostly saturated fat (not a bad thing!), and a solid chunk of monounsaturated. Unlike other oils, butter has a small amount of protein and carbohydrate, which is at least partly responsible for the very low smoke point. Additionally, as we saw before, it’s one of the least resistant fats to oxidation. This means that butter is pretty terrible overall as a cooking fat.
Butter is also definitely not Paleo, however, it does fall under the primal umbrella of foods. Since butter kind of sucks as a solid, if you do opt to use butter to cook, do so at a low heat. Also, store it in an airtight container in the fridge to avoid oxidation.
Clarified butter, also known as ghee, is a byproduct of butter. Unlike butter, it has an extremely high smoke point. If you’re planning on doing higher temperature cooking, choose ghee over butter, although ghee of course still isn’t Paleo.
Here’s an interesting one. Canola oil comes from the rapeseed plant, and with a name like that, you should probably have low expectations. Originally, the oil from a rapeseed plant isn’t even edible, which should raise red flags already. A compound called erucic acid has to be removed first.
If you have a bottle, look at the nutrition label; it probably says that it’s a great source of omega-3 fats. The problem with this claim, is that all (edible) canola oil is refined. Do you remember what happens when polyunsaturated fats (like omega-3s) get heated to high temperatures? That’s right, they get oxidized and damaged. That omega-3 on the label isn’t doing you any favors in real life.
Bottom line, do not eat canola oil.
Coconut products have always been a favorite of the paleo community. Coconut oil is mainly derived from the flesh of the drupe – a fruit (that’s right, it’s not a nut).
You can easily find both cold-pressed unrefined coconut oil and refined coconut oil.
Coconut is unique in that it’s almost entirely made of saturated fats. These fats are mainly medium-chain triglycerides (MCTs), which come with a whole host of benefits. While you don’t want to consume a huge amount at a time, consuming coconut oil in small doses is very healthy.
Now what about stability? Take a look at the chart where we compared the smoke point and oxidation time and you’ll see that coconut oil is by far the most resistant oil to oxidation that we looked at. Combine that with the fact that it usually comes in a tight glass jar, as long as you keep it away from light, it should last a long time (1-2 years) before you need to be concerned about rancidity.
With a smoke point of 177 degrees Celsius (350 degrees Fahrenheit), coconut oil is great for low-heat cooking.
Probably the most popular oils are also unfortunately the worst. Corn oil, sometimes just called vegetable oil, is that classic yellow oil always on sale – a giant tub for $1. We’ve also grouped in peanut oil (legume), just because it has similar properties.
Both corn and peanut oils are almost always sold as refined oils. How else would you get fat out of corn without chemical solvents?
They both have a high amount of polyunsaturated fats (32% in peanut, 59% in corn). Similar to canola oil, these fats are heavily damaged and will lead to free radical formation during the bleaching and deodorizing processes.
Do not eat corn oil, vegetable oil, or peanut oil.
Grape Seed Oil
Grape seed oil is made from, shockingly, the seeds of grapes. It’s one of the latest “superfoods” promoted, but it’s not all it’s cracked up to be.
The most important thing you need to know about grape seed oil is that it is about 70% polyunsaturated fat (almost all omega-6). This renders it terrible as a cooking oil. It has a good amount of vitamin E, but that’s about it.
While virgin grape seed oil isn’t the worst for uncooked foods, it’s far from the best and not worth its high price.
If you’re extremely strict about the Paleo diet, this is the fat you’re probably most interested in. The smoke point of lard will vary depending on the cut it came from, although most pork lard has a smoke point of about 190 degrees Celcius.
It’s typically about 45% monounsaturated fats, 40% saturated, and 10% polyunsaturated. In short, it’s fairly resistant to oxidation. Tallow is fat that comes from beef, which has a similar profile, but actually less polyunsaturated fat (a good thing).
In general, animal fats are a good choice for any cooking below their smoke point. While they don’t have any significant antioxidants, the fat profile ensures they remain relatively stable.
You can buy lard or tallow from most stores or make your own inexpensive rendered animal fat. If interested, here’s a tutorial on how to render your own lard.
Macadamia Nut Oil
Be honest, have you ever considered cooking with macadamia nut oil?
The attention that it receives is unjustly low. Just like olive oil, macadamia nuts can literally be squished to extract oil, which is great in comparison to corn and other oils that need chemical solvents. Macadamia nut oil has a smoke point of at least 210oC (some claim higher), which is equivalent to 410 degrees Fahrenheit – remarkable.
Now the problem with most nut oils is that they are filled with polyunsaturated fats, which makes them unstable under heat. Macadamia is the exception. It is made of about 12% saturated fats, 84% monounsaturated fats, and just 4% polyunsaturated fats. On top of that, it is loaded with vitamins, minerals, and phytochemicals.
Combining that oxidative resistance with its high smoke point, macadamia nut oil is great for just about any type of cooking. The one downside is that it’s more expensive than most oils, but the quality is worth it.
Opinions about olive oil have wavered greatly in recent years. Let’s settle those doubts now.
Standards of Olive Oil
Olive oil is a big business. So much so that there is an International Olive Council (IOC). Take a look at the IOC’s detailed olive oil standards here. Here’s what you need to know:
- Extra virgin olive oil: Made with the highest quality olives without chemical solvents and basic processing procedures (no bleaching or deodorizing)
- Virgin olive oil: Made by slightly lower quality olives, but still without chemical solvents and only with basic processing
- Refined olive oil: Goes through the bleaching and deodorizing processes, ruining the quality of the oil. The IOC has labeled these “Not fit for human consumption” – that should say a lot.
- Light olive oil or just “olive oil”: A blend of olive oils (virgin and refined). You’ll want to avoid these.
However, the IOC only has members from Europe, the Middle East, and South America. Olive oil in North America and other countries don’t have the same stringent guidelines.
Olive Oil Nutrition
Olive oil is primarily made from monounsaturated fats(73%), with a relatively small amount of saturated (14%) and polyunsaturated (13%) fats. But that 13% of polyunsaturated fats is somewhat concerning.
Based on everything we’ve looked at so far, you might be wondering if it’s safe to cook with at any heat. While many blindly parrot that it’s not safe – the studies say otherwise.
Olive oil is loaded with antioxidants and polyphenols, which we know can prevent oxidation from occurring. Two brands of extra virgin olive oil were heated at 180 degrees Celsius for 36 hours straight. This is just below the smoke point, which is 191 degrees Celsius (375 degrees Fahrenheit).
While you might expect some oxidation of the polyunsaturated fats to occur, here’s the important part from the journal article: “we can conclude that despite the heating conditions, VOO maintained most of its minor compounds and, therefore, most of its nutritional properties.”
The evidence is in: Quality extra virgin olive oil is great for any cooking below it’s smoke point (191 degrees Celsius). Virgin olive oil is almost as good if you are trying to keep the cost down.
Palm Oil has an attractive fat distribution, composed of 50% saturated fat, 39% monounsaturated fat, and 11% polyunsaturated. Additionally, it has a high amount of vitamin E (an antioxidant) that prevents free radical formation during cooking.
Overall, this makes it good for cooking at any temperature below its smoke point, which is low, at only 150oC for unrefined palm oil. The big problem with palm oil is that in places like Indonesia, palm oil plantations are responsible for wiping out a huge percentage of the orangutan population.
While palm oil is good for low-heat cooking, try to only buy from habitat-friendly producers if you choose to use it.
Sesame seed oil shares a lot of the same problems as vegetable oils. It contains a high amount of polyunsaturated fats (43%) and minimal antioxidants. It should not be heated much, as it will readily oxidize and form free radicals.
Most of the sesame oil sold in stores is refined, which means it’s already past saving.
Bottom line: sesame seed oil isn’t particularly nutritious and is an unstable oil that should not be used for cooking.
Are Cooking Oils Paleo?
Opinions will vary from oil to oil. For oils that can be simply squeezed out from paleo foods (like olive, coconut, macadamia), it’s reasonable to conclude that these oils can be considered Paleo.
For those that need chemical extraction, it’s reasonable to conclude that these are not paleo, as this wasn’t possible until very recently.
Which Paleo Cooking Oils Are the Best?
If you’ve made it this far, well done.
One important point about cooking with oils in general: As we’ve seen, the higher temperature that you cook at, the higher risk for oxidation and formation of detrimental compounds. Whenever possible, cook at low temperatures.
Let’s finish off by summarizing the best oils. It turns out that all of the top cooking oils are also paleo, perhaps with the exception of ghee.
- Coconut oil: The most stable oil from a paleo favorite. It’s high saturated fat content comes with health benefits on top of cooking excellence. Suitable for any cooking below 177 degrees Celsius.
- Macadamia nut oil: The underated nut oil has an excellent fat distribution and antioxidant content, making it high stable even under high heats (with an incredible smoke point). Suitable for any cooking below 210 degrees Celsius.
- Extra virgin olive oil: The extremely high amount of antioxidants in olive oil protects the polyunsaturated fats from oxidation. Suitable for any cooking below 190 degrees Celsius.
- Animal fat (lard/tallow): Straight from animals, it doesn’t get any more Paleo than this. Animal fat has a great fat distribution, even though it isn’t highly nutritious. Suitable for cooking below 190 degrees Celsius.
Now of course the best oil for you will depend on what you’re cooking, and which oil tastes you like or dislike. You now have 4 safe and healthy options that are suitable for most dishes, which will you choose?
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