It's gory stuff and sure to have made the firm's management wince, especially since the final 20 minutes is an account of Spurlock's attempt to engage McDonald's in dialogue. Dozens of calls are made to the firm's US chiefs, whose refusal to talk will embarrass PROs in the audience.
But the extreme nature of Spurlock's experiment - and McDonald's belated, more combative reaction to it - leave it unclear at this stage how far the brand will be damaged by this latest attack on its reputation.
Anti-Spurlock ads taken out in UK
In the UK, McDonald's took out full-page anti-Spurlock ads in The Times, The Independent and The Guardian. Ads also appeared in the Scottish media during the Edinburgh International Film Festival, at which Spurlock appeared, and a website has been set up at supersizeme-thedebate.co.uk.
Written in a tone that has won praise among marketers for its unstuffiness, the ad says: 'The film is slick, well-made and, yes, somewhat annoyingly, doesn't portray McDonald's in the most favourable light.'
One corporate PRO lauds McDonald's UK response, saying: 'It has taken a proactive response to this film and that is the best thing McDonald's could do. I can't fault it.'
Tartan Films, Super Size Me's UK distributor, in turn took out an ad in The Times, thanking McDonald's for 'promoting not only the film but also the issues raised in the film'. The ad also 'wished all the best' to Helen Steel and Dave Morris, the anti-McDonald's campaigners whose lengthy legal fight is now in the European courts.
McDonald's UK head of corporate affairs Nick Hindle reflects: 'Where ten years ago it was eco-warriors, now it's food-warriors.' Asked whether the PR team wanted respite from the agitproppers and anti-obesity campaigners, Hindle replies: 'Not at all. Such attacks give us a chance to tell our story. But we do get fed up if journalists don't cover the changes we are making.'
These include the launch of salads and Fruit Bags, plus the ditching of its 'supersize' meal option - announced just weeks after the movie's premiere at the Sundance Film Festival. A coincidence? 'Customers just weren't buying it,' claims Hindle.
At a London preview of Super Size Me last week, McDonald's V-P Julian Hilton-Johnson attended a post-film panel debate. The flak he received from members of the public illustrated the depth of anti-McDonald's feeling among a certain strata of society (not that he needed reminding: few anti-globalisation protests take place without the customary chair smashing through a McDonald's window).
Another panelist at the debate was Charlie Powell, project officer at Sustain, the umbrella group that campaigns for ethical food policies and practices. 'McDonald's is expert at marketing, but not so good on the PR side. It's missing the big tricks,' he says.
Referring to the growing lobby to curb marketing to children, Powell says: 'McDonald's could engineer a huge PR coup if it voluntarily ceased to promote its food directly to children. It would get applauded everywhere.'
Culture secretary Tessa Jowell and Ofcom have ruled out an outright ban on advertising junk food to children, but the long-awaited Public Health White Paper is due later this year.
One former McDonald's UK PR adviser says: 'The fear is that restrictions (on marketing to kids) will slip on to Labour's re-election manifesto.'
The UK obesity stats are telling and McDonald's is right in the firing line - 8.5 per cent of six-year-olds and 15 per cent of 15-year-olds are obese. Warnings from watchdogs such as the Food Standards Agency will continue to spill into the media.
Tartan Films admits Super Size Me is unlikely to dent McDonald's global sales, which rose more than five per cent year-on-year this June (the brand's 13th successive month of global sales rises following a heavily publicised fall last year).
One corporate PRO says: 'These figures show that McDonald's has taken great steps to fight back (on issues such as obesity), but there have been some unnecessary knee-jerk reactions. Their fruit promotions were clearly rushed, and it didn't appear to account for the fact that its salads contain so much fat.'
The PRO says McDonald's must avoid losing sight of the fact that it is first and foremost a burger seller: 'It needs to shout more about its burgers and not be embarrassed about them.'
Hindle himself says: 'There will be more changes to the menu and more (PR) activity aimed at developing an understanding as to how (McDonald's food) fits into a balanced diet.'
McDonald's is all too aware that the likes of Spurlock are ready and willing to take a pop if the brand's products - and promotions - disappoint.
MCDONALD'S: PR FACT-FILE
UK contacts: Head of corporate affairs Nick Hindle
Head of press and PR: Amanda Pierce
Head of internal comms: Alison Carruthers
Europe contacts: V-P communications Mike Love
Corporate comms director: Eddie Bensilum
Senior manager, European communications: Louise Marcotte
UK agencies: Bell Pottinger Public Affairs issues management, lobbying;
The Red Consultancy consumer PR and football sponsorship PR
Blue Rubicon promotes employment practices