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Toxic Compounds Found in Oil Used for Frying Foods


If you need another reason to skip fried foods, here it is: a study recently detected toxic compounds called aldehydes in fried foods.

If you need another reason to skip fried foods, here it is: a Spanish study recently detected levels of toxic compounds called aldehydes in fried foods. These toxins are linked to certain types of cancer, as well as diseases such as Alzheimer’s and Parkinson’s.

It was previously known that these compounds are created when oils such as sunflower oil are heated at very high temperatures—temperatures necessary to fry foods—and the toxins can be inhaled and contribute to atmospheric pollution. What wasn’t known before this study was conducted was that the toxins remain in the food and can be consumed. According to the study, “The fact that significant concentrations of these toxic compounds were found in some oils before the oil reached 25% of the polar compounds is a cause of concern for human health.”

Interestingly, the study noted that healthy oils (polyunsaturated oils such as flaxseed oil and sunflower oil) were the most damaged at high heats.

How to avoid aldehydes in food
As far as avoiding toxins go, this one is easy—don’t eat fried foods! Choose whole, unprocessed foods whenever possible and avoid fast food.

When preparing meals at home, be aware of how to use different types of cooking oils. Many oils can be perfectly healthy and have many health benefits when used properly.

  • Always avoid all trans fats and hydrogenated oils.
  • Limit your intake of saturated fats (with the exception of coconut oil). 
  • Don’t cook with oils that have very low smoking points, such as flaxseed oil. Rather, use these in salad dressings and poured on top of foods.
  • Use only low heat with oils such as olive oil.
  • Oils such as grapeseed oil can be heated at higher temperatures. (But still avoid deep frying!)
  • Check out these tips for more information!


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Matthew Kadey, MSc, RDMatthew Kadey, MSc, RD