When you eat a burger and fries from a fast food restaurant, you're ultimately chowing down on corn.
Researchers figured this out by going on a burger-buying spree, collecting hamburgers, chicken sandwiches and French fries from the big three fast-food chains around the country and doing chemical analyses to find out the ultimate source of the animal meat and cooking oil that go into those meals.
The findings, detailed in the Nov. 10 issue of the journal Proceedings of the National Academy of Sciences, showed that the cows and chickens that make up fast food sandwiches are fed almost exclusively corn and that French fries are almost universally cooked in corn oil.
Study leader Hope Jahren of the University of Hawaii said that the work sheds light on corn's agro-economical importance as a source of cheap feed, as well as the lack of transparency for the consumer as to where their food ultimately comes from.
Fast food nation
Fast food chains make up more than half of all the restaurants in the United States and sell more than $100 billion worth of food each year.
As meat consumption has skyrocketed in recent years, so has fast food consumption and associated health problems, such as diabetes and obesity. Just one cheeseburger, one chicken sandwich or one small order of fries accounts for 50 percent of a consumer's daily recommended calories, 80 percent of carbohydrates, 75 percent of protein (90 percent for women) and a full day's serving of fat.
All this makes fast food "a decent proportion of the American food supply," Jahren told LiveScience.
Fast food companies don't raise their food themselves, of course — their meat and chicken are supplied by a chain of various distributors. Conventionally raised cows and chicken are generally fed corn that has been fermented into a delectable feed inside a silo — corn is cheap and high in calories, meaning the animals get fatter faster (which means faster revenue streams for cattlemen).
Jahren and her colleague Rebecca Kraft wanted to test fast food to see if they could find corn's signature in the burgers and fries being served across the country. Corn has a unique signature of carbon-13 (an isotope of carbon, or form of the element with more or fewer neutrons than is typical) that persists even when converted into an animal's meat.
The researchers purchased fast food from McDonald's, Burger King and Wendy's at three locations each in six major American cities: Los Angeles, San Francisco, Denver, Detroit, Boston and Baltimore. At each location, they bought three hamburgers, three chicken sandwiches and three small orders of fries. (Jahren and Kraft did not receive any outside funding for the study.)
Samples of the meat, chicken and fries were freeze-dried and then blended up in a lab so that their carbon isotope signatures could be analyzed.
Of the 160 samples of beef analyzed, 93 percent, or all but 12 samples, were from cows fed an exclusively corn-based diet, the results showed. (The 12 differing samples all came from Burger King restaurants along the West Coast.)
All of the chicken samples indicated an exclusively corn-fed diet and were extremely homogeneous, meaning the meat from many chickens is processed to make a chicken patty.
"How many animals does this thing contain?" Jahren said, adding that the uniform carbon signature in the chicken "shows the extent to which this thing is homogenized."
For French fries, Wendy's used a corn-based oil, while McDonald's and Burger King used other vegetable oils, the analysis revealed.
For Wendy's in particular, no item sampled could be traced back to a non-corn source.
"It all comes back to corn," Jahren said.
The problems inherent in corn-based food production don't necessarily stem from the nutritional content of corn itself.
"Corn has a reasonable place in the diets of animals and humans," said Marion Nestle, a professor of nutrition at New York University.
However, cows would not naturally eat corn, as they evolved to eat and digest grasses. Farmers rely on corn because grasses are less economical as a feed.
"From the standpoint of nutrition and the environment, feeding cattle on grass would be ideal but even I don’t think that is entirely practical," Nestle wrote LiveScience in an email.
The issue is complicated, Nestle said, because corn is highly subsidized by the federal government and those subsidies make "concentrated animal feeding operations" (called CAFO's) possible. In CAFO's, animals are crowded together and allowed little movement; these operations "have truly dreadful effects on the environments of the communities in which they operate, are not healthy for animals, and overuse antibiotics, which affects human health," Nestle wrote.
Jahren and Kraft also measured levels of nitrogen-15 in fast-food samples, which indicated that the corn grown for feed and oil was heavily fertilized, which also can have significant local environmental impacts.
Lack of information
One point the study does highlight is the dearth of information on food production available to the consumer.
"I think the point the authors are trying to make is that most people aren’t aware of the extent to which corn ingredients permeate the food supply," Nestle wrote. "I do think that many people would like to know more about where food and food ingredients come from."
Jahren contacted all three fast food companies and combed their Web sites for information tracing the chain of supply of their products because she wanted to compare the results of her study to the company's sourcing information.
"None of this information is available to the consumer," Jahren said.
Wendy's spokesman Bob Bertini told LiveScience that "we can't speak to the merits of the study," but added that "Wendy's does not own, raise, transport or process livestock. However, we are committed to the humane treatment of animals by our suppliers. We've worked for many years with Dr. Temple Grandin, one of the world's leading animal welfare experts, to strengthen our beef, pork and chicken welfare programs."
McDonald's referred LiveScience to the American Meat Institute for comment.
An AMI statement on the study disputed the need for additional consumer information on the sourcing of fast food products, noting that consumers "appear satisfied with the current nutrition and ingredient information available upon request or on signage in restaurants."
"A 2008 survey by the International Food Information Council (IFIC) polled consumers about what information they are interested when analyzing food packages. The data do not suggest any measurable interest in information about production practices and livestock or poultry feed. While this information may be of keen interest to the authors, it does not appear to be top of mind with U.S. consumers," the statement added.
The statement also said: "We also question why they selected beef and poultry from three particular restaurant chains as the basis for the study. The U.S. meat and poultry industry produces the same products for other chains and for retail grocery stores."
Jahren and Kraft noted that they chose the specific chains because they are the top-selling fast-food companies in the nation. The also noted that the European Union, as well as Canada and Australia, have more regulations on the tracking of food production, partly due to consumer demand for the information.
Burger King declined to comment on the study.