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For his documentary Super Size Me, Morgan Spurlock spent a month eating nothing but items off the McDonald’s menu. The McDiet’s repercussions on Spurlock’s physique provided Super Size Me’s most convincing argument. Fast Food Nation expands the diagnoses to consider the industry’s effects on America’s body politic.

Dazed and Confused filmmaker Richard Linklater teams with Eric Schlosser, author of the 2001 nonfiction exposé Fast Food Nation, to fictionalize the book’s arguments. Downbeat but passionate, Fast Food Nation tries to show, rather than tell, the social impact caused by a country of junk-food junkies.

The film follows three stories from different sides of the process that converts Bossie to an all-beef patty in your stomach. Greg Kinnear, Hollywood’s go-to guy for playing callow suburbanites, plays Don Anderson, a marketing vice president at Mickey’s, “The Home of the Big One.” Anderson’s scenes provide some humorous seasoning to Fast Food Nation’s frequently grim fare. In a room resembling a pharmaceutical lab, Anderson can taste a sample off a cardboard strip and suggest that the “Calypso Chicken Tenders” could use a hint of lime.

Anderson’s boss asks him to quietly investigate allegations that one of Mickey’s major beef suppliers in Colorado has shipped product with fecal contamination—or, as he bluntly puts it, “There’s shit in the meat.” As Anderson talks to diverse members of the Mickey’s corporate “family,” the line reverberates through the movie.

The Colorado meat plant employs a largely undocumented workforce, whom we follow beginning on the Mexican side of the border. Sylvia (Catalina Sandino Moreno) and her loved ones endure a perverse kind of Underground Railroad, which delivers them from poverty to a kind of indentured servitude.

Just around the corner from the plant stands, inevitably, a Mickey’s franchise, where Amber (Ashley Johnson), a studious teenager on the brink of college, works behind the counter. A friend asks Amber how she can work for a company that harms the environmental and national health, and she counters, “Not all of us can get hired at Banana Republic,” implying that even the best choice is another huge corporation.

Seemingly every ambitious film of today explores its big themes through a sprawling tale of interlocking narratives, but Fast Food Nation justifies the approach with both its far-reaching subject and its metaphorical value. You might say that it’s equally interested in the “Nation” part of the title as much as the “Fast Food.” Chain restaurants and the meat industry aren’t just the unifying conceit, but a convenient stand-in for what could be called America’s corporate caste system, with its rich executives, poor service workers and practically invisible industrial laborers.

Fast Food Nation doesn’t try to hide the politics on its sleeve. When Amber’s cool uncle (Ethan Hawke) stops by for a visit, he helps kindle her idealism while begging her not to get pregnant and stuck in the small town. Amber falls in with some campus would-be activists, but even a daring act of civil disobedience proves ineffectual and suggests that neither cattle nor American citizens can easily think outside the box.

One of the final scenes takes place on the meat plant’s killing floor. Even if you’re an unrepentant steak lover, it’s a harrowing sequence. The shock tactic prompts viewers not just to reconsider the ethical treatment of animals, but of human beings involved in the system as well. Fast Food Nation can change your thinking about who really deserves a break today.

FAST FOOD NATION ( * * * )

Directed by Richard Linklater. • Starring Greg Kinnear and Catalina Sandino Moreno. • R, 114 min. • At the Osio Cinemas.