Obesity can increase risk of 13 different cancers
Piling on the pounds increases risks of cancers, according to new research.
The finding highlights the importance of keeping in shape to help reduce the risk of these cancers as people get older.
Scientists have identified eight different forms of the disease linked to being overweight or obese.
They include those of the stomach, liver, gallbladder, pancreas, ovary and thyroid - along with a type of tumour called meningioma and the blood cancer multiple myeloma.
It adds to evidence from the same team in 2002 connecting excess weight to cancers of the colon, gullet, kidney, breast and womb.
The findings are based on a review of more than 1,000 studies of weight and cancer risk analysed by the World Health Organisation's International Agency for Cancer on Research.
Professor Graham Colditz, who chaired the France-based IARC Working Group, said: "The burden of cancer due to being overweight or obese is more extensive than what has been assumed.
"Many of the newly identified cancers linked to excess weight haven't been on people's radar screens as having a weight component."
The study published in The New England Journal of Medicine said keeping in shape could help to reduce risk of these cancers as people get older.
It could have a significant bearing on the global population where an estimated 640 million adults and 110 million children are obese.
Earlier this year research showed Britain will be the fattest nation in Europe within a decade with almost four in ten adults obese.
Currently obesity rates are 28.4 per cent for women - the second highest in Europe behind only Malta - and 26.2 per cent for men, the worst in the continent.
Prof Colditz, of Washington University in St Louis, said: "Lifestyle factors such as eating a healthy diet, maintaining a healthy weight and exercising - in addition to not smoking - can have a significant impact on reducing cancer risk.
"Public health efforts to combat cancer should focus on these things that people have some control over.
"But losing weight is hard for many people. Rather than getting discouraged and giving up those struggling to take off weight could instead focus on avoiding more weight gain."
For most of the cancers on the newly expanded list the researchers noted a positive dose-response relationship - in other words the higher the BMI (body mass index) the greater the cancer risk.
These were similar for men and women and when data were available consistent across geographic regions - North America, Europe, Asia and the Middle East.
There are many reasons why being overweight or obese can increase cancer risk, said the researchers.
Excess fat leads to an overproduction of oestrogen, testosterone and insulin and promotes inflammation - all of which can drive cancer growth.
Prof Colditz said: "Significant numbers of the US and the world's population are overweight. This is another wake-up call. It's time to take our health and our diets seriously."
The study was published in The New England Journal of Medicine.