Being overweight is responsible for 7.5 per cent, or 13,200 cases of cancer in the UK alone.
Experts now warn that obesity is set to cause more cancer in women than even smoking.
According to researchers, being overweight increases the risk of 13 different types of tumour, including cancer of the breast and womb.
But only one in seven women realises there is a link, says Cancer Research UK, which has launched a major campaign to highlight the dietary dangers.
The charity further wants ministers to take the same tough approach to weight problems as smoking, rates of which have fallen steadily.
They say that measures must include ban on junk food TV ads before 9pm and a crackdown on promotion of fattening snacks.
CRUK said smoking causes 12 per cent of all cancers in women, or around 22,000 cases a year. However, being overweight is responsible for 7.5 per cent, or 13,200 cases.
But the gap is closing at such a rate that the two could be neck and neck in under 20 years.
Any by 2043, obesity will be the biggest cause of cancer in women.
Speaking about it, CRUK spokeswoman Professor Linda Bauld said, “Obesity is a huge public health threat and will only get worse if nothing is done.”
She further added that the Government must build on the lessons of smoking prevention to reduce the number of weight-related cancers by making it easier to keep a healthy weight and protect children.