David Biello summarizes a new study:

If you thought you were eating mostly grass-fed beef when you bit into a Big Mac, think again: The bulk of a fast-food hamburger from McDonald's, Burger King or Wendy's is made from cows that eat primarily corn, or so says a new study of the chemical composition of more than 480 fast-food burgers from across the nation.

And it isn't only cows that are eating corn. There is also evidence of a corn diet in chicken sandwiches, and even French fries get a good slathering of the fat that makes them so tasty from being fried in corn oil.

"Corn has been criticized as being unsustainable based on the unusual amount of fertilizer, water and machinery required to bring it to harvest," says geobiologist Hope Jahren of the University of Hawaii at Manoa's School of Ocean and Earth Science and Technology, who led the research. "We are getting a picture of the American diet on a national scale by using chemistry, which is quite objective."

(Hat tip: 3QD)