Blaming a computer software error, the US government has admitted overstating the nation's weight problem in a study last year that said that obesity was about to overtake smoking as the chief cause of death in America.

The study, conducted by the Centres for Disease Control and Prevention and published last March in the Journal of the American Medical Association, said that between 1990 and 2000, obesity-related deaths climbed to 400,000 a year - an increase of 100,000. In the journal's latest issue, the government said the increase was 65,000 deaths.

Donna Stroup, acting director for the CDC's coordinating centre for health promotion, attributed the mistake to a software error.

The original study put the number of tobacco-related deaths a year at just under 435,000, and contended that more Americans could soon be dying from obesity than from smoking if the trend persisted.

Despite the correction, the agency maintained that obesity was still a major cause of death.