Does cooking make your oil dangerous?

Befuddled about which oil to use? Here’s how one expert clears up the confusion.

Almost any oil, including extra-virgin olive oil, is fine for most types of home cooking.

“Olive oil, due to its chemical structure, is susceptible to oxidative damage when heated,” says

“When it comes to high heat cooking, coconut oil is your best choice,” says

“Coconut oil is the best oil you can use for cooking because it can resist heat-induced damage, so you can avoid ingesting oxidized fats,” says

Oxidative stress—that is, an excess of free radicals caused by oxidation—may damage DNA and raise the risk of cancer, heart disease, and other illnesses. But your oil is unlikely to become oxidized in the frying pan or wok.

“For the amount of time you’re going to cook, and the temperatures you’re going to get to, your oil is not going to undergo oxidation,” explains Eric Decker, an oil expert and chair of the department of food sciences at the University of Massachusetts Amherst.

What’s more, adds Decker, “every oil naturally contains vitamin E, which is an antioxidant.”

Extra-​virgin olive oil has another plus. “It isn’t refined, so it has a lot of naturally occurring antioxidants.”

Decker’s take-home message: don’t worry about oxidizing oils on your stovetop. “If you’re just pan-frying, no oxidation probably occurs. Even with deep-fat frying at home, oxidation is minimal.”

So fear of frying is no reason to stop using monounsaturated oils (olive, peanut, canola) or polyunsaturated oils (soy, corn, sunflower), which lower LDL (“bad”) cholesterol, and switch to coconut oil, which raises LDL.

Smoke Point

Some oils do hold up better at high temperatures, though. Any oil starts to degrade once it reaches its smoke point, which varies from oil to oil. “If you put oil in the pan and heat it too much or let it go too long, the oil starts smoking,” Decker says.

And then you could be in trouble. “The smoke point is followed by the flash point,” notes Decker. “That’s when your oil catches on fire.” If you accidentally let your oil smoke, get rid of it and start over.

Refining an oil raises its smoke point by removing impurities, which is why refined oils—like most canola, soy, and peanut, as well as “light” or “pure” olive oil—work well for high-temperature cooking.


Do oils ever become oxidized? Yes, but it’s easy to tell when that happens. “When oxidation occurs, the fatty acids break into small molecules, which have a smell,” says Decker. “That’s what we call rancidity.”

But a high temperature isn’t the biggest cause of oxidation, says Decker. It’s time.

“I just cringe when I see people buying five-gallon containers of soybean oil, because there’s no way—unless they’re deep frying every day—they’re going to use it up before it goes rancid.”

While all oils can become oxidized, “the more unsaturated the fat is, the more susceptible it is,” adds Decker.

What to do

“Buy smaller bottles and store them in the refrigerator,” says Decker. “That’s what I do at home. And if your oil smells bad, don’t use it.”

There’s no need to keep olive oil cold, though. “It will harden in the refrigerator,” says Decker. “Plus, it’s more stable than polyunsaturated fats. So you can keep it at room temperature.”

The bottom line: For home cooking, almost any oil should be fine. Coconut oil? For your heart’s sake, leave it on the shelf.

Photo: © Grafvision/


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The information in this post first appeared in the March 2018 issue of Nutrition Action Healthletter.

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9 Replies to “Does cooking make your oil dangerous?”

  1. I grew up on olive oil. Never used canola because of the (to me) putrid smell and taste and have always been suspect of coconut oil and consider it a fad.
    Recently, usng the FODMAPs elimination and reintroduction process, I have realized everything soy and coconut cause me major GI problems.
    Olive oil is part of my cultural upbringing and probably part of my DNA. The other things aren’t. Too soon old and too late smart.

  2. I liked the article but the last line about keeping coconut oil on the shelf for your heart’s sake was confusing. The article says that coconut oil is the best for cooking. When you leave something in the shelf it usually means that you don’t touch it. What does the author mean here? I’m confused. Is coconut oil good or bad?

    1. Hi Melissa,
      Thanks for your question. Because of its adverse effects on heart health, we don’t recommend that people eat coconut oil. So, while it performs well as a cooking oil, it doesn’t support heart health and we suggest you use a different oil for cooking.

  3. Thank you for all of your work, and your informative articles. I, too, would like to see the research that supports this. I noticed the person quoted said it “probably” wouldn’t get oxidized. Thank you!

  4. Article discusses frying with oil. I roast a lot of vegetables in the oven using olive oil for the most part. I also often “grease” baking pans with Crisco or real butter for baked goods. Is it safe to bake with oils? And, are some better than others? What about reusing bacon grease, such as for cooking eggs?

  5. For the past year I have been using 100% pure avocado oil for almost all cooking and salads. I really like it and it has a smoke point of 500 degrees F. My local Walmart carries it but I can’t find any impartial mention of it in any Nutrition Action release. Please let me know more about this product.

  6. I cook in cast iron pans, which have been seasoned over the years with the cooking oil used in them. Do users of cast iron need to worry that this coating has oxidized in a dangerous way?

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