Forbes: A study from the Proceedings of the National Academy of Sciences contains controversial claims about menu items served at McDonald's, Wendy's and Burger King.
Using a technique that identifies carbon and nitrogen isotopes in meat, co-authors A. Hope Jahren and Rebecca Kraft tried to determine the animals' diets and in what conditions they were raised. Based on the high levels of carbon and nitrogen isotopes found in the meat products, the authors claim that the cattle and poultry were predominantly fed corn, which makes them as fat as possible in as short a time as possible, and were raised in extreme confinement.
Other scientists questioned the conclusiveness of the study's findings while noting consumers' increasing interest in the origin of their food.
