Where does your food come from? This is a question central to the Gordian knot of issues tangling together public health, environmental health, energy markets, and geopolitics. It is increasingly on the lips of “localvores” seeking to enhance both their own health and that of the land around them by eating locally grown food that is wholesome and does not require massive expenditure of fossil fuels to transport it to the plate. It is obviously a question at the heart of vegetarianism.
For many Americans, the food comes, most immediately, from the local fast food joint, arriving wrapped in a mountain of paper and plastic packaging (the recently popular phrase “lipstick on a pig” comes to mind) at the take-out window while the car sits idly, spewing carbon and other stuff into the air.
But where does it come from before that? Answering that question is surprisingly difficult. And that, it emerges, is no coincidence. The fast food industry, which runs more than half the restaurants in the USA and sells more than a hundred billion dollars of food each year, have consistently opposed regulation of ingredient reporting. Enter Hope Kahren and Rebecca Kraft, who set out on a scientific detective mission to answer that question and recently reported their results in an open access article in PNAS. The results, perhaps predictably, are not pretty.
The authors dusted for fingerprints, as it were, using stable isotope analysis. Isotopes of carbon are used commonly in scientific sleuthing of where food comes from and who eats it, both in natural food webs and in what might be called the human food web. The background is this: Carbon has two naturally occurring stable (i.e., non-radioactive) isotopes, that is, two forms of the element that differ in the number of protons in the nucleus, having either 12 or 13. The two types of carbon basically function in the same way chemically and biologically; however 13C is a slightly heavier than 12C, with the result that it tends to gets left behind when plants are sucking CO2 out of the air to photosynthesize and make new plant biomass. The result is that the ratio of the two forms or isotopes of carbon in their tissue, their so-called carbon isotopic signature, differs from the ratio in the atmosphere out of which they sucked it. Plants that are less selective, and thus suck more 13C, are said to have a “heavier” ratio than pickier plants that suck less 13C. The technical term for this difference in isotopic ratio between the plant (or animal, as the case may be) tissue and the atmosphere is the δ13C ratio (pronounced “del C-13”, del being short for the lower case delta, which is used by science geeks to signify a difference, in this case between plant tissue and the standard against which it’s being compared). Animals (like cows and us) that eat the plants (like corn) retain the carbon isotopic signature of their food, so it can be used to figure out what they’ve been eating.
Right. So why do we need to know this stuff? Well it just so happens that corn has a rather unique “light” carbon isotopic signature that is readily distinguishable from those of many of the other crops at the base of the human food chain. The authors of this paper took advantage of corn’s unique carbon isotopic signature to explore the rather unsavory (pardon the pun) question of where fast food comes from.
Jahren and Kraft used C and N stable isotopes to suss out the source of feed to the animals used in fast food, the source of fat within Freedom French fries, and, ingeniously, were able to interpret these data to infer the role of artificial fertilizer use and confinement of the animals in the industrial fast food production chain. They sampled >480 hamburgers, chicken sandwiches and fries from McDonald’s, Burger King, and Wendy’s outlets in Los Angeles, San Francisco, Denver, Detroit, Boston, and Baltimore. Personally I prefer diving in the Caribbean for my field work, but — hey — they got a PNAS paper out of it. Here’s what they found:
” Based on a comparison with [isotopic values of different livestock feeds], 100% of the chicken and 93% of the beef sampled in this study had δ13C values consistent with an exclusively corn-based diet.” Indeed, isotopic signatures indicated that only 12 of the 162 hamburgers they sampled could possibly have come from cattle fed anything other than corn. So forget the bucolic vistas of cattle peacefully grazing in green pastures with tinkling cowbells. We’re talking about industrial meat factories.
But wait — there’s more:
Jahren and Kraft also measured the isotopic signature of nitrogen, the δ15N. This signature tells a different part of the story. The signature of nitrogen in livestock ultimately reflects the source of fertilizer used, but also correlates with animal stocking rate. It turns out that the burgers and chick-o-patties sampled from America’s fast food outlets (over 90 billion sold! OK, I made that up but it’s probably within a few orders of magnitude) have unusually high and consistent δ15N signatures: “We observed remarkably invariant values of δ15N in both beef and chicken, reflecting uniform confinement and exposure to heavily fertilized feed for all animals.” The results are shown in the graph above, which I included mostly because of its pleasing, mandala-like arrangement of colored dots. The different symbol shapes are different fast-food chains, with three samples (rows) from three restaurants (columns) of each chain in each of seven cities.
The bottom line: Throughout the whole country (and presumably elsewhere in the world, where the Golden Arches and their ilk are increasingly blocking out views of the Arc de Triomphe, the Great Wall, etc.), a principal source of calories and fat to the populace is provided by a food industry that is not only grossly unhealthy, a blot on the landscape, and numbingly inhumane, but also destructive to the environment. In what way? Corn agriculture has gotten black eyes lately because of its tremendous appetite for water and fertilizer, with much of the latter running off into the Mississippi, the Gulf of Mexico and Chesapeake Bay, where it nurtures hypoxic dead zones. Now we can see that, perversely, much of that pollution is being driven by the American appetite for junk food (not to mention the growing, and wildly misguided, move toward bioethanol fuel production).
Why are we learning this only now? Well, one reason is the way the fast-food industry is structured: “Fastfood corporations do not raise livestock, but instead buy it from other companies. Birth, growth, and slaughter are distinct events occurring at different facilities, often under different companies. Each fast food chain employs distributor companies: These suppliers organize and broker the production and transport of meat to the site of food fabrication and sale. In this way, distributors act as a barrier to consumer information; suppliers relevant to this study provide little information beyond their use of ‘local farms’ that feed ‘mixed grains.'” Clearly, The latter claim at least is fiction, as these results demonstrate.
One more piece of evidence that what you don’t know can hurt you. So [warning: self-righteous pontification follows!] slow down and eat local foods. And, if there is a single no-brainer message that comes out of all of this, it is clearly this: stop eating meat. You’ll be healthier, you’ll greatly reduce your environmental footprint, and you won’t have those frightful chicken and beef factories on your conscience. As a personal disclaimer, I haven’t succeeded entirely in doing that — yet — but I’m working on it . . .
[Original source: Jahren, A.H. and and Kraft, R.A. 2008. Carbon and nitrogen stable isotopes in fast food: Signatures of corn and confinement. Proceedings of the National cademy of Science of the USA 105 (46): 17855-17860.]