EARLY buzz about Richard Linklater’s Fast Food Nation as a Cannes competition front-runner quickly turned stale after the muted response to the first press screening.

The first part of Linklater’s double-pronged assault on the festival (his rotoscope animation, A Scanner Darkly, will be shown next week in the festival sidebar, Un Certain Regard), the film is a fictionalised interpretation of Eric Schlosser’s crusading book on the fast-food industry and its dubious practices.

The multistrand structure and the tone of righteous outrage make this a kind of Syriana-lite for a more unsophisticated palate.

Initially, there are two main stories. A likeable Greg Kinnear is Don Henderson, an executive at Mickey’s Fast Food Restaurants. The aggressively expanding burger chain is enjoying record profits thanks to Don’s innovative marketing of their trademark meal: the Big One.

Don, though, finds himself exploring the flipside of the bestselling burger when he is sent to investigate the meat processing plant that keeps Mickey’s in its Big Ones. An independent study shows that there is an unacceptable level of faecal contamination in their meat (what, I wonder, would be an acceptable level?). Meanwhile, the film also follows a group of illegal Mexican immigrants across the border and into low-level grunt work in the hellish processing plant.

Despite the presence of the excellent Catalina Sandino Moreno, it is difficult to shake the suspicion that the Mexicans are just narrative pawns who will be sacrificed to demonstrate corporate callousness.

With each new scene it feels as though we are marking time until some gruesome industrial accident or management misdeed.

The somewhat schematic plotting apart, the early part of the film shows plenty of promise, largely thanks to Kinnear’s big-hearted performance and the rueful humour that he brings to the role of a man who realises that he has sold his soul to a company that has, quite literally, been feeding him s***.

The picture tails off when Kinnear’s strand is dropped from the narrative and Amber (Ashley Johnson), a teenage worker in a burger restaurant, comes to the fore; and with the entrance of Ethan Hawke as Amber’s right-on uncle, any semblance of subtlety leaves the film.

Earnest young environmentalists (including, bizarrely, the rock star Avril Lavigne) preach on the evils of the local meat plant and the film’s tone becomes more didactic by the minute. Furious, fact-filled polemics from teenagers are not the best way to get a message across.

And the film fails to do the one thing that could have made a difference: tell us something that we don’t know.