Where does your food come from? You might say it comes from a supermarket, a fast-food restaurant or a convenience store. Where it probably doesn't come from is a healthy, family-run farm. Old MacDonald is now a costumed shill for the conglomerates that control our diet from seed to shelf.

In exposing the unsavory practices of agribusiness, the muckraking documentary "Food, Inc." cuts to the bone. It doesn't just suggest that farms have become factories — it infiltrates the teeming facilities where animals are fattened on corn, disease is bred on the assembly line and workers are treated like disposable parts.

For those who have been paying attention, much of this material is familiar. The food-conglomerate angle was covered in a less-ambitious documentary called "King Corn," and a more-ambitious documentary called "The Corporation" touched on the menace of the multinationals; but this one hits the sweet spot, and it does it with style.

The imagery ranges from the dreamy seduction of the supermarket to the nightmare of the slaughterhouse, and director Robert Kenner even enlivens the dry statistics.

The most powerful portion of the film focuses on a familiar name: Monsanto. Now that the Supreme Court has allowed corporations to patent life forms, the company pursues and punishes farmers who save seeds from one season to the next.

Although the execs wouldn't comment on camera, many are now mobilizing their PR departments to counter the film. They say American consumers are lucky to have so many choices. Yet until very recently, the system has been rigged against those who choose to opt out.

Ironically, a semblance of choice is coming from one of the biggest corporations of all: Wal-Mart, which now is highlighting organic products. Although "Food, Inc." closes with an activist pep talk, the likelihood of real change remains hard to swallow.