There has been a “dramatic rise” in deaths in England in which obesity was a contributory factor, researchers say.
They said death certificates showed there were 757 obesity related deaths in 2009, compared with 358 in 2000.
There were likely to be many more such deaths where obesity was not recorded, the University of Oxford team said in the European Journal of Public Health.
It comes as the Scottish government warned of a “ticking time bomb”, saying 40% of Scots could be obese by 2030.
One public health expert said people often did not realise obesity was linked with many serious conditions.
The researchers said as obesity was rarely listed as the main cause of death, a simple snapshot of death certificates would not have picked up the rise.
The marked increase was apparent when they included contributing causes of death in the analysis.
Other figures recently released by ministers showed more than 190 people under 65 died as a direct result of obesity in 2009 compared with 88 in 2000.
When contributing factors were included, there were 757 obesity related deaths in 2009 compared with 358 in 2000.
About a quarter of adults in the UK are now obese.
Obesity and problems caused by being overweight are thought to cost the NHS more than £3bn a year.
The Scottish government said 40% of Scots could be classed as obese by 2030, if things do not change.
Scotland’s Public Health Minister Shona Robison is due to launch an anti-obesity strategy later.
Study leader Professor Michael Goldacre said although the death certificate figures tallied with rises in levels of obesity in the population over the same period, they did not know before the study whether doctors would be recording obesity on death certificates.
“We know for example obesity contributes to heart disease but if someone dies of heart disease you don’t necessarily expect doctors to note if they were obese.
“But this shows doctors are increasingly recognising obesity as a cause of death.”
He added: “One of the key messages is you can’t rely on underlying causes alone - if you don’t look at other causes you cannot see what is contributing to disease.”
Professor Alan Maryon-Davis, president of the Faculty of Public Health, said people in the “early stages” of obesity did not often realise how dangerous being overweight could be and their weight commonly “creeps up” without them noticing.
“People do not realise how closely linked it is with serious conditions, such as heart disease, stroke, high blood pressure and diabetes.
“We have to take obesity seriously.”
By Emma Wilkinson
Health reporter, BBC News