Fast-food chains are more likely than smaller restaurants to cook their french fries in corn oil, which is higher in cholesterol-raising saturated fats than other vegetable oils, a study from the University of Hawaii found.

Almost 70 percent of the national fast-food chain restaurants such as McDonald's and Wendy's in Honolulu used corn oil mixed with other oils for their french fries compared with 20 percent of independent restaurants, according to research published online in the Proceedings of the National Academy of Sciences.

UH researchers Hope Jahren and Brian Shubert purchased fries from 68 of the 101 national chain fast-food restaurants on Oahu and from 66 small businesses using their own money. They analyzed the oil in the fries and concluded that fries at mom-and-pop restaurants are slightly healthier than the big chains.

McDonald's, Burger King and Wendy's said previously they switched to vegetable fry oils to remove trans fats. The trans fats raise cholesterol levels in the blood and may increase the risk of heart disease, according to the American Heart Association. Still, the Hawaii researchers said, the fry oil used now by the chains includes corn oil that is higher in saturated fats, which also raises cholesterol.

“;This shows that we're making progress, but there's benefit to eating in small local restaurants from a health perspective because of the different oil sources,”; said Louis Aronne, director of the Comprehensive Weight Control Program at New York Presbyterian Hospital/Weill Cornell Medical Center, in a telephone interview last week.

Aronne, who wasn't connected to the study, said corn oil has the least favorable ratio of saturated fats to so-called good fats among commonly used vegetable oils. It is better than the oils that contain trans fat, he said.

McDonald's completed its transition to a blend of canola, corn and soy oils in U.S. restaurants in May 2008, said Danya Proud, a spokeswoman for the Oak Brook, Illinois-based company, in an e-mail.

This “;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,”; she said. “;All fried menu items on McDonald's national core menu contain 0 grams trans fat per serving.”;

Saturated fats are typically eaten in foods from animals and some plants. Trans fats result from adding hydrogen to vegetable oils for use in commercial baked goods and cooking foods in restaurants.

Fats called polyunsaturated and monounsaturated, which are found in safflower, soy, sunflower seed and canola oils, may help lower cholesterol when they are used instead of saturated fats, according to the heart association. Corn oil has a higher amount of saturated fats and is lower in the so-called good fats than other commonly used vegetable oils.

Fries from San Diego-based Jack in the Box Inc. outlets didn't show corn oil, according to the study. Although it's hard to distinguish non-corn oils, Jahren said that based on composition, the smaller restaurants probably cooked their fries in a soy oil because it is cheaper.

According to the study, 32 pounds of corn oil costs $70, while the same amount of canola oil costs $75 and soybean oil costs $50. To make corn oil cost-effective, the researchers said “;it is probably necessary to contract ingredients on a large scale from preferred distributors.”;

Jahren said restaurants aren't providing enough information about what they're using to cook foods and making it available while people are deciding what to eat.

“;Consumers really deserve more information about what's in their food and how it's made,”; she said. Fries are “;a very basic component of restaurant diets. There are very simple questions about it—how is it made? what is it fried in?—that the consumer can't get any good information for.”;