College pals Ian Cheney and Curt Ellis moved from Boston to Greene, Iowa, to grow an acre of corn after an isotope geochemistry lab at the University of Virginia found that the carbon in their own bodies actually originated from corn. During the year that followed, they learned their harvest was worth so little in the marketplace that American farmers could not survive without government subsidies. The pair set out to follow their crop through the food production system to see where it would wind up, only to discover that the genetically modified corn they grew wasn’t readily edible and it could eventually become sulfur, cow feed, or the high-fructose corn syrup found in a variety of processed foods.

Chronicling their experience, the documentary “King Corn” exposes the never-ending vicious circle of food production. Government subsidies encourage quantity over quality, so farmers grow more corn than is consumable. As a result, the excess finds its way into the American diet in processed, non-nutritious forms of ground beef and corn syrup. While its findings are certainly alarming, the film isn’t as aggressive or persuasive as “Super Size Me” or “Fast Food Nation” in presenting the issue as a polemic. You won’t likely swear off junk food as a result of watching “King Corn,” even though you’re sort of expecting it to have that effect.

Although the film has that unmistakable PBS voice-over narration (it will air on the public broadcaster next year), it resembles reality television and blurs the definition of documentary. Clearly inspired by the likes of Ross McElwee and Morgan Spurlock, director Aaron Woolf artificially staged a scenario that serves as the launching pad for the film. “King Corn” isn’t a first-person account, but one can still interpret it as such given that Messrs. Woolf and Ellis are cousins. The filmmaker also inserts himself into the frame with a dangling boom mic here and a tripod there.

Mr. Cheney and Mr. Ellis’s genealogical search for relatives of their Iowan great-grandfathers initially seems tangential but ultimately turns out to be the most rewarding aspect of the film. Faded photos in family albums and oral accounts from long-lost relatives add both a historical perspective on the devolution of the American farming industry and an unexpected poignancy that expands the scope and relevance of the film.