As an experiment, next time you're at the grocery store, read the label of everything you would normally pick out. Check the ingredients for "high fructose corn syrup." If it's there, put it back on the shelf.
The recent documentary King Corn does a whimsical and surprisingly powerful job of exploring how corn came to be the dominant crop in the United States. Two college friends, Ian Cheney and Curt Ellis, move to Greene, Iowa after graduation to grow one acre of corn. They learned, largely by accident, that both their great-grandfathers grew up in the same small county in Iowa, and they both want to connect to their lost heritage. For the sake of the film, the gimmick of growing a single acre of corn sets them on their way.
The tone of the movie is especially impressive for two reasons. One, we watch the two friends encounter their ancestry and discover how distant even Iowa has become from its oldest traditions (for example, one hundred years ago most Iowa farmers ate the crops they produced; now, very few of them can). Two, they approach the issues surrounding agriculture and health with admirable restraint and deftness. Whereas Michael Moore would be aggressive, they are calmly humane. Still, they manage to produce a pretty stunning indictment of corn production in the United States.
The short version: before the 1970s, the U.S. Department of Agriculture paid farmers to underproduce their crops. But in the mid-70s, Nixon's head of Agriculture changed the system; the government began paying farmers to overproduce. That led to an excess of corn production. In turn, the government subsidizes alternate uses of corn, including ethanol production and the creation of high fructose corn syrup, which is a cheap substitute for sugar but adds calories without adding nutrients. (When Ian and Curt make high fructose corn syrup in their home, we see just how vile it is.)
High fructose corn syrup has been linked to the greatly increased incidence of obesity and diabetes in the U.S. Unfortunately, it's in many pre-packaged foods and sodas, and most people have no idea of its effects. Thanks to King Corn, the message is spreading. With any luck, the Department of Agriculture will shift its emphasis on overproduction, and the vast excess of corn can shrink.