Ever wonder what your French fries were fried in? Like bumbling burglars who leave fingerprints at a crime scene, cooking oils leave their own clues. And by measuring the carbon isotopes in French fries, University of Hawaii researchers found that one oil tops all others as the choice to fry fries in: corn oil. That’s according to a report in the Proceedings of the National Academy of Sciences.

National chain restaurants typically reveal only that fries may contain one or more of the following oils: corn, canola, soybean, cottonseed, sunflower and palm. But consumers might like a little more info: in a meal of burger, fries and soda, 20 percent of the total calories come from the oil that fried the potatoes.

Analyzing fries from nearly 200 Hawaiian restaurants, the scientists found that 69 percent of the national chain outlets used corn oil, compared with just 20 percent of independent eateries.

Corn oil is probably the least healthy of the oils mentioned, with more harmful saturated fats than canola or sunflower and fewer heart-healthy compounds than soybean. Of course, regardless of what they’re fried in, French fries probably aren’t on your diet. Then again, you’re probably not on your diet either.

—Karen Hopkin

[The above text is an exact transcript of this podcast.]