Britain is also battling an increasing alcohol problem, which experts warned could worsen during the Olympics.

"When any major sporting event has an official alcohol supplier, it sends out completely the wrong messages to young people, making it seem as though no major event is complete without alcohol," said Sir Ian Gilmore, special adviser to the Royal College of Physicians on alcohol.

He said he "greatly regretted" that the London Olympics had appointed an official beer.

Some experts said advertising during the Olympics could actually cause a spike in fast food consumption, even in people not inclined to eat it.

"We cannot simply decide not to process (an ad), there is a subliminal association that is made that may affect your behavior in the future," said Nilli Lavie, a professor of psychology and brain sciences at University College London.

McDonald's said in a statement they expected about one-in-10 people visiting London's Olympic Park to eat at their Golden Arches.