Loosely based on the influential book Fast Food Nation, a new film by offbeat director Richard Linklater is fast food for thought. He talks to Donald Clarke

Oh, the cynicism of these folk. The faeces-riddled guts that actually lurk inside the sandwich have so little in common with the sizzling comestibles that appear in the commercial. There is, of course, something of an irony here. Richard Linklater (above), director of such fine films as Before Sunrise, A Scanner Darklyand School of Rock, is working within an industry every bit as cynical as the hamburger giants.

Indeed, Linklater has previously worked for studios that, when promoting their blockbusters, have entered into partnerships with the very companies the new film satirises.

"I suppose there are some similarities between the two industries," he says reluctantly. "You do want your film to be seen everywhere. You want to promise some experience, but, as far as production goes, it is very different. I guess the difference is that in fast food, there is the conformity element. That burger is supposed to taste the same year in, year out. You do need some variety in movies."

And, to be fair, Linklater has delivered a delicious diversity of entertainment in the 15 years since his first feature, Slacker, proved that a film about nothing, made for nothing and starring nobody could have considerable appeal.

Born in Houston, Texas, Linklater, now 45, developed his passion for movies while programming the film society at the University of Austin. Slacker, like so much of his subsequent work, was low on plot, but high on chatter.

Following a gang of bohemians as they pottered around Austin, this baggy picture - full of circular conversations - looks like the work of a committed talker. Four years later, he made the gorgeous Before Sunrise, in which Julie Delpy and Ethan Hawke blather their way about Vienna. There's more chatter elsewhere.

"I don't know why that is," he says. "When I first started making films if I had drifted towards action thrillers then I might have continued doing that. It's weird, because I am not even that much of a talker. I was never the kind to sit around the coffee shop and drone on about stuff. I don't know where it came from. Maybe it was from watching French films by people like Godard and Eric Rohmer."

In recent years, Linklater has begun alternating walkie-talkie films such as Before Sunset, an equally fine sequel to Before Sunrise, with more commercial enterprises such as School of Rock, in which Jack Black teaches kids to get down, and the somewhat underrated Bad News Bears.

Viewed from the outside, his career seems to be divided into two distinct strands. A Scanner Darkly, his weird partially animated adaptation of a Philip K Dick story, plays to the arthouse crowd. School of Rockis aimed at the multiplex. Is he conscious of switching hats when moving from one strand to the other?

"No, I genuinely am not," he says. "I have never gone into a movie thinking, 'This is a commercial film; I must approach it differently.'

"And you have to remember that these are still lower budgeted studio pictures. It normally feels like a safe place to be, making studio pictures. They leave you alone for the most part. Obviously, I am aware different films have different audiences."

So who exactly is Fast Food Nationfor? Schlosser's hugely influential book delivered reams of disturbing information about what goes into fast food, how the companies mistreat their workers and how they set about nabbing young customers.

The film sets out to illustrate the author's research through the stories of a loosely connected collection of people with different interests in the industry. Catalina Sandino Moreno plays an immigrant eager to find an alternative to working in the meat processing plant. Greg Kinnear turns out as an executive for a fast food firm named, provocatively, Mickey's. Ashley Johnson plays a student activist.

The film certainly works as an accompanying document for the book, but its plots are, perhaps, too diffuse to engage on an emotional level.

"We started with the characters," he explains. "Then we spent a long time - maybe a year or so - working out what they were all going to do. It actually was Eric who said: let's just throw out the book. Let's just have this be the stories of this collection of people at different points in the food chain. What we have ended up with is a very irregular sort of adaptation."

Indeed, one might reasonably ask if it is an adaptation at all. Linklater's film bears much the same relationship to Schlosser's text as Woody Allen's Everything You Always Wanted to Know about Sex bore to David Reuben's book of the same name.

"Yeah, we kept the name and little else," he laughs. "It's a good title though . . . It is a companion piece. If you have read the book, then maybe this will hit you in a different part of your psyche. Film is a great medium to get across a message. If this helps people understand the plight of, say, undocumented workers, then it's worth doing. They are regarded as a rung up from terrorists these days."

Still a resident of Austin, Linklater is one of a significant band of Texan artists who are doing their bit to reverse the negative image that state has acquired. Listening to him quietly detail his outrage about the treatment of migrant workers, one finds one's respect returning for the Lone Star State.

"Yeah that reputation has gathered because of one guy who came from there," he says. "Firstly let me address that. George Bush is not from Texas. He is from Connecticut. He tried to get into the University of Texas Law School, but they have some standards, so he had to go to Harvard. Actually, it's a shame he didn't get in to Texas, because he might have had to actually read the constitution." That's the spirit. Good man, Richard.

Fast Food Nationopens on