The Omnivore's Dilemma: A Natural History of Four Meals

by Michael Pollan

Some carbon atoms, called isotopes, have more than the usual complement of six protons and six neutrons, giving them a slightly different atomic weight. C-13, for example, has six protons and seven neutrons. (Hence “C-13.”) For whatever reason, when a C-4 plant goes scavenging for its four-packs of carbon, it takes in more carbon 13 than ordinary—C-3—plants, which exhibit a marked preference for the more common carbon 12. Greedy for carbon, C-4 plants can’t afford to discriminate among isotopes, and so end up with relatively more carbon 13. The higher the ratio of carbon 13 to carbon 12 in a person’s flesh, the more corn has been in his diet—or in the diet of the animals he or she ate. (As far as we’re concerned, it makes little difference whether we consume relatively more or less carbon 13.)