In a paper just published in PNAS, scientists use stable isotopes to estimate the contribution of corn to the standard American diet of meat and fries from fast food. They sampled a disgustingly large number of not so happy meals from Burger King, McDonald's, and Wendy's and used this form of analysis to determine that a very large percentage of the tissues that make up these meals originate as corn.
How did they do this, and does this finding matter? Well, it's complicated but I'm happy to explain, and yes, it matters.
This research used carbon (C) and nitrogen (N) stable isotopes to reconstruct the history of meat (beef and chicken). The carbon isotope signature tells us whether or not the animal ate a particular type of grass, which would include but not be limited to corn, during later stages of development. The more grass of this particular type, the more shifted the carbon signal is in a certain direction. The nitrogen isotope signature is not as easily interpreted, and in fact, it's meaning is empirically derived. It is reasonable to assume that certain nitrogen values mean that the original plant matter from which animal tissue is formed comes from highly fertilized industrialized farms, but N values can also vary because of geographical factors and other things that I will not go into here.
The reason the carbon signal works is this: There are two isotopes of carbon that are reasonably common, stable, and that make up the index number used in this kind of analysis. Meanwhile there are two (simplifying slightly) basic ways in which plants conduct photosynthesis.
In most contexts either of these two carbon isotopes work the same way ... which is why they are called isotopes of one element! Different stable isotopes vary only a tiny bit in molecular weight owing to the presence or absence of one little bit in the atom that is seemingly not important as to how each atom behaves. However, it turns out that these two different processes of photosynthesis treat each of these two carbon isotopes differently, differentially using one more often than the other in building complex molecules. So, if you start with a known ratio of these two carbon isotopes in the CO2 being used by the plant, the resulting carbohydrates the plant produces will have a shifted ratio, and this shift will be different for one type of photosynthesis than the other.
Tropical grasses, including corn (which evolved as a tropical grass) have one system of photosynthesis, and temperate grasses have the other. So, if cattle are fed sometimes on the range in North America, and sometimes with corn silage, there will be a mixture of temperate (wild) and tropical (corn) grasses contributing to the C ratios in the food, and thus in the tissues the cattle make out of this food as they grow. If cattle are fed only corn, they will have a very different ratio of carbon isotopes than if they are only range fed in temperate North America.
The long and the short of it is that fast food hamburgers and chickens are astonishingly corn-fed, if this analysis is correct.
I can think of one possible problem with this analysis, which the researchers address but not adequately. Cattle from tropical countries will look just like corn-fed cattle. The nitrogen signatures are consistent with this not being true, but in fact, do not rule it out. The fact that we don't really know where these cattle come from is a bit disturbing in its own right. While I suspect this effect may be important, I very much doubt the conclusions of this analysis would be affected very much by the presence of tropical beef or chicken in the samples.
Why is this disturbing? Two reasons, depending on your perspective.
If you are someone who eats, you should know that our food supply is based on corn. This means that the food supply is vulnerable to crash if this one element ... corn ... crashes. And it can crash.
It does not matter that you don't ever eat fast food. (Who does, after all? Certainly not you or me!) As pointed out in this paper, this apparent corn dependence is not confined to the three big fast food chains and their beef and chicken. It does not matter if you are a vegetarian either. If the corn supply crashes, the meat supply crashes, and the meat eaters, who tend to be well armed and organized, will come after your vegetables.
The other reason this matters is because of the financial structure of the food industry. I do not honestly know how much of an effect subsidies have on corn production, but it is the case that corn production is subsidized. This means that not only are there a few varieties of a single species grown using one method to provide us with a large percentage of our food, but the financial structure on which this industry is built is to some extent similarly undiversified and thus possibly vulnerable.
What is the solution? First, plant a garden! If everyone who could plant a garden did, a measurable percentage of our food supply would be not based on the industrialized corn industry and we would all get more exercise. Then, while you are waiting for your tomatoes to ripen, ask our politicians what they are doing about this. Make this an issue for the next election. Go to your party's platform conventions and bring this up as an issue for discussion. Learn about it. Blog about it.
Speaking of learning and blogging, here are some more posts on this research.
Fast food = corn, corn, and more corn
Corn is everywhere in American fast food
A. H. Jahren, R. A. Kraft (2008). Carbon and nitrogen stable isotopes in fast food: Signatures of corn and confinement Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.0809870105
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2007 Documentary: King Corn
It isn't just meat production that's dependent on corn. Ask someone who's allergic to corn about trying to find safe processed food.
Absolutely. Corn is everywhere. The fried chicken sandwich and the french fries may be fried in corn. Corn syrup may be used in the bun. The soda ... the sugar in the soda ... may be corn syrup.
... this is making me hungry.
An interesting study, but of course, a completely nonsurprising result. The dependence of the commercial meat industry on corn-based feed is pretty well known. An enormous portion of the grain grown in this country goes to feed animals, not people. And those guys didn't even get into the prevalence of high-fructose corn syrup, which along with hydrogenated vegetable oil, makes up the "food plasma" of processed foods.
I've been toying with the idea of writing about this study, since I think most people have no idea where their food comes from, or how it's harvested.
Thanks for doing it for me :)
A really good book tracing what is in our industrial foods is "Twinkie, Deconstructed" by Steve Ettlinger where he takes the ingredients from a local Twinkie (they change from time to time somewhat) and traces them literally from the ground up - from farms or mines or gas wells to the final product. Mind blowing.
Yesterday, my husband and I watched several hours of Planet Green about corn, how it's grown, how it's processed... you name it. If it was about corn, they talked about it.
One surprise to me was xanthum (sp?) gum. It's used in everything from drilling oil wells to thickening foods. And I never knew before that it was processed from corn. Silly me.
My question is -- why do we need to do anything about this other than to insure we have several varieties of corn always available?
I do not see corn as "bad" for us.
Our farmland is being used to grow animal food - very wasteful. And the feed lots and factory farms - disgusting. I guess those things won't change until we have to.
I grow a few vegetables and herbs, but growing a significant amount of the food we eat is probably not feasible for most people.
if the corn supply crashes, the meat supply does not crash. meat just gets (much?) more expensive while we switch to other feedstocks --- there's no reason beef and chicken have to be raised on corn, after all.
but the notion of having several varieties of corn available in case one should crash? yeah, that's one of those sensible ideas that most likely have nothing whatever to do with the real world. as in all aspects of major agribusiness, there are most likely only a handful of genetic strains of corn being mass produced out there, and most of them copyrighted by Monsanto; any real variety you'd have to look for among hardscrabble small-plot farms in central America, i'd bet.
Most people would be surprised to know how dependent the world is on just four crops: corn, rice, soy and wheat. Of these, corn has probably the narrowest genetic base in commercial production for a number of reasons. Exclusive use of hybrid seed which leads to the loss of locally adapted ecotypes and genetic uniformity is of course a major one. An estimated 80-85% of the dent corn grown in 1970 had Tms cytoplasm. This is not all bad; the reason these crops and practices dominate is because they are the ones that are productive and economically successful under current conditions. And the system can react fairly quickly to a crisis like a disease outbreak.
Those Central and South American small plot farmers are a valuable reservoir of diversity, and they will probably provide the cure for the next disease or insect crisis. I don't see the corn belt moving away from conventional high-input monoculture anytime soon - if some other system could compete economically, it would already be there. You could argue that subsidies and lack of accounting for externalities for things like pollution and soil erosion are propping up the status quo, and I'd agree to some extent. But that's the environment the farmers have to deal with, and they are the ones that grow the crops. I think any radical change is going to lead to lower production and higher food costs. My guess is this is going to be due to much higher energy costs and I have a hunch it is about 1 or 2 decades away. Combined with increasing world population, I am afraid we are looking uphill at an onrushing avalanche. I hope I'm wrong.
Uncle Noel
If you live in a house and have a yard - remove all the grass, patio etc and turn the yard into productive garden - you'd be surprised at just how much food you can grow . Urban dwellers with no yard, well there are a lot of flat rooftops that could be used for gardens, bonus is that it helps with rainwater runoff and thermal control of the structure as well as the surrounding area. As the economy weakens further, or if there is a disaster in corn production, or fuel becomes scarce which interrupts the delivery of goods, there will be/are a lot of office towers/warehouses/stores that could be converted into indoor farms. There are a lot of possibilities.
Whee! We just watched King Corn in my food and society class last week. Also see Michael Pollan's Omnivore's Dilemma. Glad for the paper reference on corn isotopes; I couldn't find one, and didn't have the time to search properly last week before class.
One problem with the analysis - sugarcane is also a C4, so I would think that means the results of "corn" carbon have a lot of sugar carbon hiding out in there as well. Not nearly as much, but still some.
My students are even now trying to eat for a few days without any corn or corn products in their diet, using the two-page (three-column) list of corn ingredients I gave them as a guideline. Heh.
What do you mean?
Carlie: Good point. David: The thing is that corn is a tropical grass, and corn and tropical grasses are "C-4" ... in writing the above post I avoided the terms C4 and C3 but that is what I was talking about. C4 is the photosynthetic process that tropical grasses use, C3 is used by temperate grasses. Corn is a tropical grass outside it's native environment, so it shows up as a sore thumb in temperate regions (which, by the way is a clue to the bigger problem .. look how much work it takes to get this tropical grass to grow in, say Minnesota!!!)
I doubt that sugar cane is a big effect in Carbon ratios in cattle, but who knows ... maybe there is a lot if sugar cane in silage in, say, Florida (where there is a lot of sugar cane and a lot of cattle)
Anyone know?
But yes, where 'sugar' is being used in any product, from the hamburger rolls to the coke and sprite, you would not be able to tell sugar cane from corn using these carbon isotope ratios.