Which Oils Are Best For Cooking?
Heating up certain oils can create harmful compounds and create other problems. Find out how to cook with oil safely.
I’ve talked about the pros and cons of various oils and how to store oils in previous articles but several of you have asked me to talk more specifically about what happens to oils when you heat them up and which ones are safest to cook with.  In fact, a few different things can go wrong when cooking with oil.
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Which Oils Are Best for Cooking?
If you’ve ever put some oil in a skillet to heat and then gotten distracted by a phone call or something on TV, you very likely ended up with a kitchen full of acrid black smoke and a wailing smoke alarm. That is bad. Not only is the oil unusable but the smoke that’s produced when oil is overheated contains harmful chemicals that you don’t want to be breathing in.
What Happens When Oil Gets Too Hot?
Not only do you not want your oil to smoke, ideally you don’t even want it to get hot enough to start changing color, because that is an indication that the oil has started to chemically degrade. When oil starts to break down, free radicals form, along with other harmful compounds.
Different oils have different smoke points, of course. Some oils will start to smoke at just slightly over 200 degrees Fahrenheit; others hold steady past 500 degrees. Obviously, if you’re going to be cooking at high temperatures, you want an oil with a higher smoke point.
What Determines the Smoke Point of Oil?
Contrary to popular belief, the amount of saturated or unsaturated fat in a cooking oil is not a very good indicator of its smoke point. Grapeseed oil, for example, is very high in polyunsaturated fat and has a very high smoke point, whereas soybean oil, which is also quite high in polyunsaturated fat, has a fairly low smoke point. And coconut oil, which is among the highest in saturated fat, is in the middle of the pack in terms of smoke point.Â
See Resources, below, for a link to fatty acids in common cooking oils.
The Difference Between Refined and Unrefined Oils
How pure, or refined, the oil is plays a much bigger role in determining the smoke point. The refining process removes impurities from oil, which generally increases the smoke point. Unrefined (or extra virgin) olive oil, for example, has a smoke point of about 375 degrees F. Refined (or light) olive oil has a smoke point of 465 degrees F or so. Quick and Dirty Tip: Cheaper oils are refined using a chemical process. For a bit more money, you can buy oils that are refined without chemicals and these will be your best bet.
See Resources, below, for a link to smoke points of common cooking oils. Quick and Dirty Tip: Â Â Once an oil has been heated, its smoke point will be lower.
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Which Oils Create Harmful Compounds When Heated?
But avoiding smoking oil isn’t all you need to worry about. Oils that are high in polyunsaturated fats (such as corn, soy, sunflower and other seed oils), form a harmful compound called HNE when they’re heated. That happens even in oils that are highly refined and have a high smoke point  HNE ends up in the food that are cooked in the oil and is taken up in the body, where it can have damaging effects.Â
Now I don’t want to over-state the dangers. Your body has an impressive capacity to defend itself against harmful compounds. Good thing, because it’s impossible to completely avoid them. Then again, given the realities of modern life, your defense and detox systems are probably getting a pretty good workout. So, why not minimize our exposure to toxins wherever we can. One way to minimize your exposure to HNE is to avoid cooking highly polyunsaturated oils like corn, soy, and all-purpose “vegetable” oil.
And the longer or more frequently you heat up oil, the more HNE it will contain, which is why it’s really not a good idea to reuse cooking or frying oil.  Consider that one more reason to limit your consumption of fried foods. Most restaurants not only fry foods in polyunsaturated oils, but reuse the oil over and over again.
What Oils Should You Use?
Taking all of this into consideration, here are my recommendations for the best oils to use in the kitchen.
For high-heat cooking, such as frying, searing, grilling, stir-frying, or roasting: I suggest light (or refined) olive oil, avocado oil, clarified butter (also known as ghee), refined palm, or coconut oil. Â All have a high smoke point and are low in polyunsaturated fats.
For medium-heat cooking, such as gentle sautĂ©, stewing, baking, or braising: Any of the above would work fine. For extra flavor, you could also choose a filtered, extra virgin olive oil.Â
For use off heat, such as salad dressings or drizzling over a finished dish: For maximum flavor, choose an unfiltered extra virgin olive oil, unrefined or toasted nut and seed oils. If you want a neutral flavor, canola oil would be my choice, because it’s higher in monounsaturated fat and omega 3s than most other vegetable oils.
What Causes Oil to Get Rancid?
Unfortunately, even if it never gets near the heat, oil will eventually get rancid just sitting around in your cupboard. In addition to smelling and tasting nasty, rancid oil contains harmful free radicals and shouldn’t be consumed.  The more polyunsaturated fat there is in an oil, the faster it will spoil. Another quick and dirty tip is to buy nut and seed oils—which are high in polyunsaturated fat—in small quantities and store them in the fridge. Oils that are lower in polyunsaturated fats, such as like olive, canola, and coconut oil, are fine stored in a cool cupboard.
Can You Create Trans Fats When Cooking?
One thing you really don’t have to worry about is accidentally creating trans fats when cooking. Transforming a regular fat to a trans fat requires more heat and pressure than you’re going to be able to generate in your kitchen.
Keep in Touch
If you have a suggestion for a future show topic, send an email to nutrition@quickanddirtytips.comcreate new email. You can also post comments and questions on my Nutrition Diva Facebook Page.  I answer a lot of listener questions in my free weekly newsletter, so if you’ve sent a question my way, be sure you’re signed up to receive that.
Have a great week and remember to eat something good for me!Â
RESOURCES:Â
Table of Fatty Acids in Various Vegetable Oils
Formation of HNE in Heated Oil
Oil image courtesy of Shutterstock
About the Author
Monica Reinagel is a board-certified licensed nutritionist, author, and the creator of one of iTunes’ most highly ranked health and fitness podcasts. Her advice is regularly featured on the TODAY show, Dr. Oz, NPR, and in the nation’s leading newspapers, magazines, and websites. Do you have a nutrition question? Call the Nutrition Diva listener line at 443-961-6206. Your question could be featured on the show.Â
