MONDAY, Jan. 18 (HealthDay News) -- Most French fries served in U.S. restaurants are immersed in corn-based oil -- usually considered the worst oil for human health -- before they're fried, according to the authors of a new study.
Corn oil contains copious amounts of saturated fat, known to contribute to heart disease.
This type of oil is also low in monounsaturated fat, which most Americans need more of, and high in polyunsaturated fat, which, in too-large quantities, can lower HDL ("good") cholesterol along with LDL ("bad") cholesterol, said Karen Congro, a registered dietician and director of the Wellness for Life Program at The Brooklyn Hospital Center in New York City.
Congro was not involved with the new study, published online this week in the Proceedings of the National Academy of Sciences.
The same research group that performed this study reported in November that corn, which has been linked to obesity, is a prime ingredient in almost all fast-food sold in the United States, either directly or through animal feed.
Chain restaurants are not required to provide "specific" information on ingredients in the food they offer, while small businesses do not have to provide any information at all.
"Restaurants don't tell you what they're using and, even if you ask them, they will be very cagey," Congro said. "It will be a blend, but the blend is never a blend of anything you want to use."
French fries are particularly worthy of study, said the authors, from the University of Hawaii-Manoa, because they contribute 20 percent of the calories from a fast-food meal via the fat in the frying vat.
And Americans get about one-third of their total calories from restaurants.
The authors focused their attention on the saturated fat content of corn oil, which is higher than in canola, sunflower or safflower oils.
The researchers bought French fries from 68 of the 101 national fast-food restaurants represented on the island of Oahu, including McDonald's, Wendy's, Burger King and others, as well as from 66 small businesses. Then they measured carbon isotope composition of the oil used to fry the food.
Almost seven out of 10 of the national chains but only 20 percent of the small businesses sold fries dipped in corn oil. Eleven percent of small businesses and 7 percent of chains used blends containing more than 50 percent corn oil, the researchers found.
The authors speculated that larger conglomerates are able to negotiate economical deals to purchase large quantities of oil from suppliers.
Corn oil content ranged from 16 percent on the low end for McDonald's, to 36 percent and even 50 percent and up in other eating establishments.
Danya Proud, a spokeswoman for McDonald's USA stated that, in May 2008, the corporation "completed the transition to a new canola-blend cooking oil in our 14,000 U.S. restaurants. This blend of canola, corn and soybean oil allows us to serve fried menu items with reduced levels of trans fat and saturated fat, while delivering the same great taste our customers expect from McDonald's."
Even if dipped in relatively healthy oils, though, French fries aren't high on any nutritionist's list of preferred foods.