Obesity causes more than 100,000 incidents of cancer in the US every year, the American Institute for Cancer Research said in estimates published on Friday.
The group, which funds research on the link between diet and the disease, said 49 per cent of endometrial cancers, which originate in the womb, and 35 per cent of oesophageal cancers are linked to excess body fat.
"It's clearer than ever that obesity's impact is felt before, during and after cancer, it increases risk, makes treatment more difficult and shortens survival," said Laurence Kolonel of the Cancer Research Centre of Hawaii.
Scientists have long seen a link between obesity and certain types of cancer, but the study - extrapolated from US cancer incidence data - is among the first to conclude the link exists on such a scale.
Researchers have yet to pin down the exact link between obesity and cancer, but some have suggested that fat tissue may produce heightened levels of sex hormones that spur cancer growth or that fat lowers immune function.
If the link is proven to be true, cancers could be expected to balloon in tandem with US body sizes.
According to the government-backed Centres for Disease Control, 34 per cent of American adults aged 20 and over are obese.
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