THURSDAY, Nov. 13 (HealthDay News) -- New research suggests that many fast-food meals begin with a single ingredient: corn.

Researchers uncovered signs of corn in food items from Wendy's, McDonald's and Burger King.

"We found that corn is not just a grain used in the production of fast food, it is the basis of all fast food," said study author A. Hope Jahren, a professor of geography and geophysics at the University of Hawaii. "Of the hundreds of fast-food meals we purchased across the country, there were only about 12 servings of food that could potentially be traced back to something besides corn."

The findings may not be very surprising considering that corn and its byproducts -- including the controversial high-fructose corn syrup -- are such an integral part of the American diet. Still, "the heavy use of corn in the U.S. food supply has been linked with obesity related to the availability of cheap, low-nutrient food," said Cynthia Sass, a nutritionist in New York City.

According to the study, Americans spend more than $100 billion a year on fast food. The study authors decided to analyze the fast food on an atomic level to discover how corn is used in the production of fast food.

A research team bought more than 480 servings of hamburgers, chicken sandwiches and French fries at fast-food restaurants in Los Angeles, San Francisco, Detroit, Denver, Boston and Baltimore. The food was freeze-dried and sent to a lab for analysis.

The findings were published in this week's issue of the Proceedings of the National Academy of Sciences.

By analyzing the biochemical makeup of the food, the researchers found that 100 percent and 93 percent of the cows responsible for the hamburgers and chicken sandwiches had lived on exclusively corn-based diets.

There was an exception: 12 Burger King burgers bought on the West Coast came from cows that didn't exclusively eat corn-based diets.

As for fries, the researchers found that Wendy's seems to only use corn oil to make them, although it says its fries may contain a number of kinds of oil. The researchers reported that McDonald's and Burger King fries seem to rely on other kinds of vegetable oils.

A spokesperson for Burger King declined to comment on the study. Spokespersons for McDonald's and Wendy's didn't return messages seeking comment.

The study authors pointed out that their research didn't include another possible source of corn in a fast-food diet: soft drinks that use high-fructose corn syrup as a sweetener.

Sass said the study provides more information about the origins of the food people eat.

"In my opinion, we're experiencing a food awakening in this country," she said. "More shoppers want to know where their food comes from and how it's grown. Consumers are starting to think about the traceability of food and connect the dots in the big picture of food production, particularly in terms of how it impacts the environment, our health and the health of our children."

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