How much corn, or maize, do you eat? You can probably count up the number of ears of corn on the cob, and maybe estimate the number of corn chips or corn tortillas you eat. You’d likely say that you eat much more as red meat, cheese, chicken, eggs, and, I hope, vegetables, not to forget a good batch of calories in sodas and other drinks that clearly aren’t corn. However, you need to consider where that meat, that cheese, those eggs, and those drink calories came from. The meat and the milk came from cattle that were fed corn for most of their weight gain or much of their milk production. Laying hens are fed mostly corn for the time that they produce eggs. Soft drinks, the full-calorie type, are sweetened with high-fructose corn syrup. (Ever tasted a kola nut by itself? I did, in western Cameroon, and I unpuckered after a few minutes.) That corn syrup likely appears in more than half of every processed food you eat – check those labels – and in the US our diet is almost entirely processed food, short of some fresh fruits and vegetables.
There’s an interesting technique to detect the broad sources of our food, by analyzing bits of our food (or even of us, say, a fingernail clipping). Remember, all our food comes from plants, directly or from the animals that eat it or the fungi (mushrooms) that grow on animal manure (very well sterilized). Plants can be distinguished into two types, called C3 and C4, based on the first steps in photosynthesis. The C4 plants are less common globally but corn, sugar cane, and sorghum are major examples. They take up carbon dioxide from the air with a “carrier” molecule than changes into a 4-carbon acid. This molecule gives up CO2 inside a special section of the leaf, effectively pumping up the level of available CO2 and allowing the plant to be more efficient in using water, light, and nitrogen. Why they don’t yet dominate the globe is another story. Now, the carbon in CO2 is overwhelmingly carbon-12, with six protons and six neutrons in its nucleus. A small portion, about 0.37%, is as carbon-13, with 7 neutrons. It’s stable, not radioactive. Its compounds react a tiny bit more slowly than those of carbon-12. So, compared to the carbon found in CO2 in the air, there’s even less carbon-13 in the sugars and the tissues made in the plant.
The C4 plants such as corn discriminate less against carbon-13 than do the C3 plants. We can detect the amount of discrimination with extremely precise (and pretty pricey) instruments called isotope-ratio mass spectrometers. We have one here at NMSU. The ratio of carbon-13 to carbon-12 stays nearly unchanged when an animal eats plant matter and then uses the carbon in making its own tissues. The same near-preservation of the ratio occurs when another animal (such as one of us) eats that animal. When animals eat a blend of foods, this isotope ratio is a corresponding blend of the ratios in the different foods. In short, if we measure this ratio in one of our foods, we can estimate what fraction of the food came ultimately from C4 plants and what fraction came from C3 plants. Here in the US, we can state that the C4 food was corn; we eat little sugar cane or sorghum; Hawaii grows cane but even more marijuana, in dollar value. To continue, Todd Dawson at the University of California, Berkeley, made such measurements of the isotope ratio. A soft drink came out as 100% derived from corn. A milk shake at 78%. Chicken nuggets at 56%. Even French fries were 23 percent corn; they’re sugar-enriched. So, if you’re a typical American, the quip is that you’re close to being a walking corn chip.
How did we get all this corn in our food chain? How does it relate to our nutrition and our health? Those, too, are other big stories. If you find insights on your own, please email me at firstname.lastname@example.org and we’ll share them in another column.
Vince Gutschick Las Cruces Academy 2009