Is deep-frying vegetables healthier than boiling?

Study Notes takes a closer look at recent medical studies, its caveats and what it means for you.

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The research

A recent study published in the prestigious Food Chemistry journal found that deep-frying or sautéing vegetables in extra-virgin olive oil is more beneficial than boiling them in water. Researchers from Spain used four methods to cook potatoes, tomatoes, eggplant and pumpkin – frying and sautéing in extra-virgin olive oil, boiling in water and boiling in a mix of water and oil.

Frying vegetables in extra-virgin olive oil increased their antioxidant capacity and the amount of phenolic compounds, which have been shown to protect against cardiovascular disease, lower LDL cholesterol and may even fight breast cancer. They also found that deep-frying, followed by sautéing, had the highest increase in antioxidants.

The caveat

“This study is done expertly in terms of good analysis, but it is extremely flawed,” says Alejandro Marangoni, a professor of food chemistry at the University of Guelph and Canada Research Chair in Food, Health and Aging.

“We all know that extra-virgin olive oil has a lot of antioxidants and phenols, that’s why we like it,” says Marangoni. “You’re frying the veggies in something that is already loaded in antioxidants and phenols, so of course it will pick it up. It’s like saying ‘I’m going to sprinkle phenols on these veggies’.”

Related: Guide to 5 common cooking oils

A better study would have been to compare deep-frying and sautéing vegetables in highly refined oils such as vegetable or canola oil, or removing all the phenolic content from the extra-virgin olive oil. “Then you could determine whether cooking in oil somehow extracts the antioxidants and phenols more. You just can’t do it with extra-virgin olive oil because it’s loaded in phenols, so of course it’s going to have more phenols. It’s a trivial result.”

The take-away

Yes, deep-frying and sautéing vegetables in extra-virgin olive oil will give you more antioxidants and phenols, but this has more to do with the type of oil than the cooking method. The same can’t be said for canola, vegetable or any type other of cooking oil.

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