Fast-food diners might be surprised to learn they're eating a lot of corn with their burgers and chicken sandwiches.

Corn is the basic ingredient in all chicken and most beef sampled at McDonald's, Burger King and Wendy's restaurants on the mainland, says University of Hawaii geobiologist Hope Jahren.

“;Out of hundreds and hundreds of samples, only 12 (beef) patties didn't go straight corn (as a food source),”; said Jahren, who had about 10 researchers working with her the past two years.

They purchased three burgers, three chicken sandwiches and three orders of fries at three restaurants from each of the three major chains in Los Angeles, San Francisco, Denver, Detroit, Boston and Baltimore.

They also sampled the fries: Wendy's used only corn oil, while McDonald's and Burger King used other vegetable oils.

Since fast-food corporations purchase their beef and chicken meat, it means the cows and chickens supplying it are on a corn-based diet.

“;Our results highlighted the overwhelming importance of corn agriculture within virtually every aspect of fast-food manufacture,”; Jahren and Rebecca Kraft reported in a recent issue of the Proceedings of the National Academy of Sciences.

Formerly at Johns Hopkins University, Jahren joined the UH Department of Geology and Geophysics in July. She is a specialist on stable isotopes and used carbon and nitrogen stable isotopes to test frozen food samples collected by her team.

“;We did not receive any private or public federal funding for this,”; she emphasized in an interview. “;Everyone donated time, travel and effort. The study was motivated by personal curiosity.”;

The researchers wanted to look at the American diet, she said. “;It would have been nice if we could go into peoples' homes and sample their dinner plate, but this is truly the next best thing,”; she said, pointing out that half of the nation's restaurants sell more than $100 billion of fast food each year.

“;When you look on a national level, it is very clear there is a corn-oil protocol,”; she said. Corn has been criticized because it is subsidized by the government and people feel it is unsustainable in terms of the amount of fertilizer, irrigation and machines required to process it as a crop, she noted.

Her researchers have tried for years to get information from fast-food corporations about how their food is made, what it contains, where it comes from and how animals are fed and treated, she said.

“;We were able to test with a very simple component, corn, but we could ask that question with respect to any ingredient. And basically, you shouldn't need high-power chemistry ... to tell you what's in your food,”; added Jahren, who said she has not eaten fast food since 2004.