A study published in the Proceedings of the National Academy of Sciences finds that most french fries served in U.S. restaurants are fried in grain oil, which is inferior to other types of vegetable oils from a health standpoint. By Karen Hopkin_ Have you ever wondered what kind of oil the fries you're feasting on are fried in? Just like the fingerprints left at a crime scene by a dumb burglar, identifying cooking oil can take advantage of the unique clues it leaves behind. By examining the carbon isotope content of french fries, researchers from the University of Hawaii have found that one cooking oil is way ahead of the rest when it comes to french fries: grain oil. The study was published in the Proceedings of the National Academy of Sciences. Cooking oils used in U.S. restaurants for French fries include: grain oil, castor oil, soybean oil, cottonseed oil, sunflower oil, and palm oil. However, just knowing this is not enough for consumers, who may not realize that 20% of the total calories in a meal consisting of a hamburger, fries, and a soda come from the fat used to fry the fries. Researchers analyzed french fries served at nearly 200 local restaurants in Hawaii and found that nearly 70 percent of large chain restaurants used grain-based oils to fry their fries, compared to only 20 percent of small, independently owned restaurants. Grain oil is probably the least healthy cooking oil known, containing more harmful saturated fats than castor oil or sunflower oil, and less heart-healthy compounds than soybean oil. Of course, until they know all this, many people don't touch this junk food at all. But then again, there are a few people who like french fries after all.