More than 22,000 cases of cancer every year could be prevented if the whole population was a healthy weight, researchers said.
Researchers said 63% of the UK population is overweight or obese - one of the highest levels in Europe - and body weight increases the risk of cancers of the pancreas, breast, bowel, oesophagus, kidney, womb and gall bladder.
The World Cancer Research Fund (WCRF) said 18% of the 123,000 weight-related cancer cases in the UK could be prevented every year.
The WCRF's Continuous Update Project (CUP) found that 1,257 cases of pancreatic cancer could be prevented every year if patients were a healthy weight.
Professor Alan Jackson, chairman of the CUP panel and professor of human nutrition at the University of Southampton, said: "A significant number of cancer cases could be prevented by people maintaining a healthy body weight.
"Through keeping levels of body fat low, a lot of people will avoid getting cancer in the first place - forestalling the pain and anguish associated with the disease.
"The CUP report published today looks specifically at pancreatic cancer, which is the fifth most common cause of cancer death in the UK with very low survival rates.
"Fewer than one in five patients survive the first year after diagnosis but we have found that 15% of new cases could be avoided every year by keeping body weight within the healthy range."