Tougher action on obesity urged
26 August 2011 Last updated at 06:31 BST
Tougher action - including taxing junk food - is needed by all governments if the obesity crisis is going to be tackled, experts say.
The international group of researchers, who have published a series of articles in The Lancet, said no country had yet got to grips with the problem.
They said changes in society meant it was getting harder for people to live healthy lives.
Branwen Jeffreys reports.