Obesity is to overtake smoking as the leading cause of preventable cancer in British women, according to a new paper.
If trends continue, obesity-related cancers could account for 23,000 cases by 2035, compared to 25,000 caused by smoking in the same year, said the report by Cancer Research UK.
By 2043 obesity is likely to cause more cancer cases than smoking.
The conclusions were based on projections, and researchers stressed that there remain many uncertainties in predicting what will cause cancers in the future.
As fewer people smoke and obesity rates increase, however, the gap will continue to close.
With higher rates of obesity and fewer smokers among women than men, the narrowing is happening faster among women.
The charity is now launching a campaign to raise awareness of the link between cancer and obesity, and to encourage a healthier lifestyle.
It said only around one in seven people in the UK are aware of the link between obesity and cancer.
"The decline in smoking is a cause for celebration. It shows how decades of effort to raise awareness about the health risks plus strong political action including taxation, removing tobacco marketing and a ban on smoking in indoor public places, have paid off," said professor Linda Bauld, a prevention expert at the charity.
"But, just as there is still more to do to support people to quit smoking, we also need to act now to halt the tide of weight-related cancers and ensure this projection never becomes a reality."
Measures suggested following the research including a ban on junk food adverts before 9pm and restrictions on promotions of unhealthy food and drink.
"Obesity is the new smoking, one of the greatest public health challenges of our generation," a spokesperson for NHS England said.
"Expanding waistlines also mean a heavier burden for taxpayers which is why, as we draw up a long term plan for the NHS, we are exploring all options to help patients to help themselves and help the NHS."