Super Size Me, which follows a film-maker as he eats only McDonald's fast food for an entire month, opens in the UK on Friday.
The film-maker put on 25lbs during his burger-and-fries diet
Doctors warned Morgan Spurlock his health was at risk as he munched his way through dozens of Big Macs and Chicken McNuggets and slurped gallons of cola.
The fit and healthy US documentary maker put on 25lbs and was urged by medical experts to call an end to his 30-day fast food diet.
At turns informative, shocking and black-humoured, the film asks searching questions of the US food industry and suggests a healthier alternative is available with political will.
Spurlock ate nothing but McDonald's food for 30 days
Spurlock becomes so unwell during the film that at one stage his doctor comments that the diet has affected his health to the extent that his liver "is turning into pate".
Spurlock is seen describing himself feeling ill and low in energy, while medical concerns are raised about his blood pressure and cholesterol.
The film's release has already prompted McDonald's to release a statement defending its menus and denouncing Spurlock's movie as "unrealistic".
McDonald's has called for a "balanced debate" on the film
It took out adverts in five British newspapers saying its food should be eaten as "part of a balanced diet".
In March this year the company announced it planned to scrap its supersize meals by December, and planned to introduce more lower-calorie and lower-fat options.
McDonald's has faced legal action over obesity in the US, where one group of children claimed its food was responsible for health problems.
But it has been robust in defending the "nutritional value" of its food, and has called for a "balanced debate" on Spurlock's movie.
In its UK newspaper advert it pointed out that an average customer would take more than six years to eat as much as Spurlock.
"The film is slick, well-made and yes, somewhat annoyingly, doesn't portray McDonald's in the most favourable light," the advert said.
"We've always been famous for our hamburgers and our fries, but we wouldn't suggest that they are anything other than part of a balanced diet.
"What we do agree with is its core argument - if you eat too much and do too little, it's bad for you. What we don't agree with is the idea that eating at McDonald's is bad for you."
The company highlighted details of its salads and fruit bags, which it said had led to a 10% worldwide sales increase.
It has also gone on the offensive In Australia - where the film broke box office records for a documentary - accusing Spurlock of "distortion".
His movie won the best director award at the prestigious independent US movie festival Sundance.
But McDonald's has said it does not expect it to have an impact in the UK because "there's nothing new here".