Using a carbon isotope to identify the type of feed eaten by the animals whose meat goes into hamburgers, and the oil used to cook fries, researchers were able to establish that nearly all fast food consumed in the US relies on corn agriculture.
The study was the work of Dr A Hope Jahren, Professor in the Department of Geology and Geophysics at the University of Hawaii, in Honolulu and colleague Rebecca A Kraft, and was published online before print on November 10 in the Proceedings of the National Academy of Sciences.
Over 100 billion dollars a year is spent on fast food in the US wrote the authors, adding that fast food meals contain a disproportionate amount of meat and calories within the American diet.
By looking for its carbon isotope signature, it is possible to detect the presence of corn in food, even to the point of knowing whether animals have been raised on it.
It is also possible, using the nitrogen isotope signature of fertilizer, to tell how much exposure animals that go into meat production have had to heavily fertilized feed and thus infer the extent of their confinement (which is arguably the extent to which they are not raised in a “free range” environment).
Jahren and Kraft bought over 480 servings of hamburgers, chicken sandwiches and fries from some of the biggest chains in the US: McDonald’s, Burger King, and Wendy’s. They and other researchers visited outlets in Los Angeles, San Francisco, Denver, Detroit, Boston, and Baltimore, cities that are widely spread throughout the US.
Out of the 480 samples, only 12 servings of beef did not show traces of the carbon isotope signature for corn (delta 13C), thus showing that the source cattle had been fed on other ingredients.
The researchers wrote that they found “remarkably invariant” values of the nitrogen signature (delta 15N) for fertilizer in both beef and chicken, which they inferred reflected “uniform confinement and exposure to heavily fertilized feed for all animals”.
They also examined the delta 13C values of fries: this varied significantly among restaurants, suggesting that the different chains used different mixtures of oil for deep frying. Wendy’s used only corn oil, but McDonald’s and Burger King apparently used other vegetable oils, which is not what they put in their ingredient reports, said the researchers.
Jahren and Kraft concluded that:
“Our results highlighted the overwhelming importance of corn agriculture within virtually every aspect of fast food manufacture.”
Jahren said in an interview reported by the Honolulu Star Bulletin that the study was “motivated by personal curiosity” and the researchers funded it themselves: there was no private or federal funding.
She said she and her colleagues had been trying for years to get fast food companies to reveal their food ingredients, processes, and sources, including how the meat animals are raised and what they are fed.
Jahren said there was clearly a corn-oil protocol working at a national level. Corn production attracts government subsidies, but many people say it is not a sustainable crop because it needs a lot of irrigation equipment and fertilizer, she added.
“Carbon and nitrogen stable isotopes in fast food: Signatures of corn and confinement.”
A. Hope Jahren and Rebecca A. Kraft
Proceedings of the National Academy of Sciences, published online before print November 10, 2008
doi:10.1073/pnas.0809870105
Sources: PNAS, Honolulu Star Bulletin.
Written by: Catharine Paddock, PhD