I'll have the corn, with a side of corn

It is no secret that corn is a major ingredient in animal feed, food oils, and a wide range of food products. A new paper shows that most fast food can in fact be chemically traced back to fertilized feed corn.

The idea behind the paper is relatively straightforward. The authors use the breakdown of carbon and nitrogen isotopes in a variety of fast food - burgers, chicken patties, french fries, etc. - to trace the ingredients and feed back to their source. The only thing missing from this fascinating study is an analysis of the drinks. Whether a cola or "iced tea", the drinks available at most fast food restaurants all have the same two main ingredients: water and high-fructose corn syrup.

The analysis works because of some well-documented patterns in the distribution of carbon and nitrogen isotopes. Corn has a predictably low concentration of carbon-13, because of a strong bias against this "heavier" isotope of carbon during photosynthesis. So much so that if you measure the relative proportion of the carbon-12, the more common isotope, and carbon-13 in the tissue of one of us corn-fed North Americans, you'll find much less carbon-13 than you would in the tissue of a more rice-fed Asian person [and definitely less than in the tissue of a hunter-gatherer from the last ice age]. The basic chemistry shows that North Americans are built from corn.

Nitrogen isotopes also come in handy. They can be used to determine whether chemical fertilizers were used in raising the crops that were fed to the animals or used to create the french fry oil. Fertilizer nitrogen tends to include less of the nitrogen-15 than naturally derived soil nitrogen, because the processes that make nitrogen available in the soil bias against the heavier isotope. So by combining the nitrogen and carbon isotope results, the authors are able to trace fast food items back to their origin:

From the entire sample set of beef and chicken, only 12 servings of beef had
13C < 21‰; for these animals only was a food source other than corn possible. We observed remarkably invariant values of
15N in both beef and chicken, reflecting uniform confinement and exposure to heavily fertilized feed for all animals. The
13C value of fries differed significantly among restaurants indicating that the chains used different protocols for deep-frying: Wendy’s clearly used only corn oil, whereas McDonald’s and Burger King favored other vegetable oils; this differed from ingredient reports

The conclusion is an indictment of North American fast food:

Fast food corporations, although they constitute more than half the restaurants in the U.S. and sell more than 1 hundred billion dollars of food each year (18), oppose regulation of ingredient reporting‡. Ingredients matter for many reasons: U.S. corn agriculture has been criticized as environmentally unsustainable
(19) and conspicuously subsidized (20). Of 160 food products we purchased at Wendy’s throughout the United States, not 1 item could be traced back to a noncorn source. Our work also identified corn feed as the overwhelming source of food for tissue growth, hence for beef and chicken meat, at fast food restaurants. We note that this study did not include an examination of beverages served, which are dominantly sweetened
with high fructose corn syrup (21). In 2002, the European Union adopted Regulation 178 (11) requiring suppliers to trace the origin of materials used for production. At this time in the United States, such tracing is voluntary and seldom-invoked. Our work highlights the absence of adequate consumer information necessary to facilitate an ongoing evaluation of the American diet.