The politics of food-5: Tracking the corn in our food

(This series of posts looks in detail at some of the fascinating aspects of food production identified by Michael Pollan in his book The Omnivore’s Dilemma (2006). All page numbers refer to that book, unless otherwise noted. Other related posts can be found here.)

One of the surprising things I learned is that it is possible to track corn as it proceeds through the food chain, even as it is transformed into other things.

One thing that many people do not realize is the amount of a plant’s weight that comes from the air. If you ask people where most of a plant or tree’s mass comes from, they will likely say that it comes from the ground, absorbed through the roots. But most of a plant is carbon, and this carbon was initially in the air as carbon dioxide. During the photosynthesis process, plants absorb this carbon dioxide, retain the carbon, and release the oxygen back into the atmosphere. Some of the water the plant absorbs also comes from the water vapor in the air. Pollan says that in the case of corn, 97% of the plant comes from the air and only 3% from the ground. (p. 22)

Carbon atoms in the atmosphere contain two kinds (called isotopes) of carbon atoms: those containing a total of 12 protons and neutrons (called C-12) and a much rarer isotope that contains a total of 13 (C-13). The chemical properties of these two isotopes are almost identical so that they are usually equally likely to take part in the chemical and biological processes of life. But not always. It turns out that the photosynthesis process is one situation where they differ slightly and this enables us to distinguish the carbon in corn from the carbon in almost all other plants.

It turns out that most plants during photosynthesis create compounds that contain three carbon atoms. Such plants are called C-3 plants. But a very few plants (corn and sugar cane are examples) make compounds that contain four carbon atoms (C-4). It turns out that C-4 plants have a larger C-13/C-12 isotope ratio than C-3 plants, and this signature can be used to identify the amount of carbon in plants and animals that originate in corn (or sugar cane). Thus we can track the amount of corn-based carbon in our food. (p. 21)

The way corn has dominated our diet so that we have become a nation of corn eaters can be seen in how much of the carbon content of a typical McDonald’s meal originates in corn: soda (100%), milk shake (78%), salad dressing (65%), chicken nuggets (56%), cheeseburger (52%), and French fries (23%). (p. 117) Since one in five of all meals in America are eaten in the car (a number that I found to be disturbingly high), we can see how the corn in fast food is dominating our diet. (p. 110)

Perhaps the most telling marker of the power of corn has been the rise of the now ubiquitous high-fructose corn syrup, which has become the sweetener found in almost all processed food. It is surprising to learn that high fructose corn syrup did not even exist until 1980 but now about 530 million bushels of the annual corn harvest is turned into 17.5 billion pounds of it. (p. 103)

But all this corn production and subsidies does not necessarily mean that corn farmers are raking in the dollars. It turns out that most of this money goes to the big agribusiness giants like Archer Daniel Midland (ADM) and Cargill, and food processors like Coca-Cola and Kellogg that turn the corn into finished products like high fructose corn syrup. For example, for every dollar consumers spend on eggs, 40 cents goes to the producer. But for every dollar spent on corn sweeteners, only 4 cents goes to the grower. ADM, Coca-Cola, and Kellogg get most of the rest. (p. 95)

So we have this situation where American farmers have incentives to grow as much corn as they can, while the government tries to keep the prices high, either by subsidies or by mandating the use of corn in fuels (in 2007, nearly 20% of the corn harvest went to ethanol), and food processors find ways to replace other ingredients in our food with corn-based products that can provide high profit margins.

Recently the price of corn has risen sharply but the relationship of the price of corn that the farmers get to the price we pay for food is not simple.

When there are cost shocks in the food production system due to changes in the commodity or farm product market, most retailers respond by passing on a fraction of their higher costs to consumers. Among factors affecting this pass-through rate is the level of processing and value-added services that take place between the farmgate and the grocery store aisle. Products that require more processing and packaging are usually less directly linked to changes in farm prices, while the price of less processed foods more closely follows the changes in farm prices. For example, changes in farm prices for eggs, fresh fruit, and fresh vegetables show up in more volatile retail prices for these less processed foods.

What people may not realize is that most of the cost of the food we purchase has little to do with the actual food.

For example, an 18-ounce box of corn flakes contains about 12.9 ounces of milled field corn. When field corn is priced at $2.28 per bushel (the 20-year average), the actual value of corn represented in the box of corn flakes is about 3.3 cents (1 bushel = 56 pounds). (The remainder is packaging, processing, advertising, transportation, and other costs.) At $3.40 per bushel, the average price in 2007, the value is about 4.9 cents. The 49-percent increase in corn prices would be expected to raise the price of a box of corn flakes by about 1.6 cents, or 0.5 percent, assuming no other cost increases.

So despite the dominance of corn in the food chain, the price of almost all our foods are do not fluctuate as widely as the prices that farmers get for their corn.

POST SCRIPT: Darwin talk

David Quammen, author of the biography The Reluctant Mr. Darwin will be the featured speaker at CWRU’s fall convocation at 4:30 pm in Severance Hall on Thursday, August 28, 2008.

The event is open to the public and more details can be obtained here.


  1. says

    I am really surprised that plants get part of their mass from the air. I knew they pulled in carbon dioxide and released oxygen, but didn’t think about the plant retaining the carbon part. It’s a shame that our diets are so heavily based in corn products that tend to pack on the weight.

  2. says

    These big agribusiness giants are really a burden on poor farmers. They don’t allow them to have the share they deserve. Can’t the government formulate a policy that these farmers get the share they deserve?
    I mean they are paying heavy taxes and the government provide heavy subsidies to support these farmers. What if government remove these giants and make a system that farmers have a direct access to the consumers or government may act as a middleman. By this, the farmers would be able to have more profits and the government would spend the share of the subsidies in other development projects. By this farmers would also be able to start their own food packaging business and earn profits on it as well.

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