HONOLULU -- While we know French fries are not healthy, researchers from the University of Hawaii looked into which fries were healthier: the ones from fast food chains or from mom-and-pop restaurants.

They sampled oil content in fries from 134 restaurants on Oahu; 68 of the restaurants belonged to national chains. The researchers tested fries from such local restaurants as Big City Diner, Rainbow’s Drive Inn, Like Like Drive Inn, Kanpai Bar and Grill and South Shore Grill.

Researchers found that 69 percent of national chains used corn oil to cook fries, which they said is less healthy than other vegetable oils. Meanwhile, only 20 percent of small Hawaii stores and restaurants use corn oil. Corn oil is higher in cholesterol-raising saturated fat than other oils such as soy, canola or safflower.

"Surprisingly, there was such a clear difference between the amount of corn oil in fast-food chains and the local mom-and-pop restaurants," UH geobiology professor A. Hope Jahren said. "Since corn oil is more expensive than other vegetable oils, we hypothesized that it would be a simple function of what was cheapest."

The study concluded that fries from local restaurants are slightly healthier.

The study was published in the Proceedings of the National Academy of Sciences.