Avocado oil has the highest smoking point. (Photo by Muffet)
If you've wondered which oils and fats are the best choices for cooking your meals, this post is for you.
The first question we need to ask is what makes an oil good or bad for cooking? Putting the cholesterol issue aside for a moment, we can say that perhaps the most important thing is how well the oil tolerates heat. We are using it for cooking, after all.
Two factors that affect heat tolerance are smoking point and oxidation. Smoking point is, as you might have guessed, the temperature at which the oil begins to smoke. It's also the point the oil starts to break down chemically. This is something you generally want to avoid, so it's usually recommended that you don't heat the oil to its smoking point. This, of course, rules out using oils with a low smoking point for cooking at high temperatures.
The second factor, oxidation, is related to smoking point in the sense that both are affected by temperature. However, oxidation also happens at lower temperatures than are needed for the oil to start smoking. Oxidation is problematic because the lipid peroxidation end-products (ALEs) it creates can wreak havoc inside the body. These products have been shown to accumulate with aging and cause problems such as liver spots on the skin.
So which oils are most susceptible to oxidation? If you've read this blog before then you already know the answer: polyunsaturated fats. In fact, polyunsaturated fatty acids (or PUFAs) tolerate heat very poorly. Not only do they oxidize when you heat them on a frying pan, they do so inside the body as well. On the other hand, monounsaturated fats are much more resistant to oxidation than polyunsaturated fats. Saturated fats are the most resistant.
This gives us a good rule of thumb when looking for fats to use in cooking: avoid oils high in polyunsaturated fatty acids. Because of their potential to undergo lipid peroxidation inside the body, I tend to restrict their consumption altogether, but even if you are a fan of vegetable oils and omega-3, using them for cooking is not a very good idea.
The table above shows the relative percentages of saturated (SA), monounsaturated (MUFA) and polyunsaturated fatty acids (PUFA) in various cooking oils and fats (data from US and Finnish food databases). They are in a decreasing order of PUFA content, meaning that the oils moist suitable for cooking are on the left and the least suitable oils are on the right.
As you can see, coconut oil has the highest SA content and the lowest PUFA content of all oils, making it very resistant to oxidation. Ghee and butter also have very little PUFA and lots of saturated fat. Based on this, butter is actually one of the best choices for cooking, although the high AGE content of butter and its tendency to brown quickly suggest to me that perhaps ghee is a better option. The reason might be that butter also contains some protein and a small amount of carbohydrate.
Palm oil and lard are somewhat lower in saturated fat than the first three, but since their MUFA content is quite high, they still make good choices for cooking. The rest to the right of these five are less than optimal. Corn oil, sesame oil, rapeseed oil, peanut oil, and canola oil are all high in polyunsaturates, making them prone to lipid peroxidation. And unless you buy them cold-pressed, they will have been heated during refining anyway, so some oxidation has probably happened before you even use them.
What about olive oil then? Even though everyone seems to love olive oil in general, there's something of a debate going on over whether it should be used for cooking purposes. My opinion is that, like the graph suggests, it's not the worst choice but it's not the best either. The smoking point of extra virgin olive oil seems to vary from 160 to 190 °C, depending on the free fatty acid content. Virgin olive oil, however, has some properties that make it more heat-tolerant than most other oils (link).
In general, the less refined the oil, the lower the smoke point. Unrefined oils high in PUFAs have the lowest smoking points (link), but high saturated fatty acid content does not necessarily guarantee a high smoking point. Coconut oil, for example, has a fairly low smoking point (177 °C, about the same as butter and lard) compared to peanut oil (227 °C). Refined avocado oil, which is mostly monounsaturated fat, appears to have one of the highest smoking points at 255-270 °C (link). Ghee is another oil with a very high smoking point (252 °C).
So which oils should you use for cooking? For sautéing and cooking at light to medium temperatures, my choice would be the ones on the left of the graph: coconut oil, ghee, butter, palm oil, and lard. If you stay below 170 °C, you're in pretty safe waters in terms of oxidation regardless of which one of them you choose. Virgin olive oil seems like a viable choice, too; just make sure the particular olive oil you're using it doesn't start smoking.
For searing, browning and other methods of cooking requiring higher temperatures, ghee and avocado oil seem like the best choices. When it comes to resistance to oxidation, ghee might take the cake, but avocado oil appears to have the highest smoking point of all oils, even though it does have 13.5% PUFAs. Still, keep in mind that when cooking at very high temperatures, some advanced glycation end-products (AGEs) are bound to be generated.
For more information on fats and health, see these posts:
Coconut Lowers LDL, VLDL and Triglycerides, Raises HDL
My Current Health Regimen
Blood Test Analysis: The Cholesterol and Saturated Fat Issue Revisited
Should Saturated Fat Be Avoided in Low-Carb Diets?