Researchers have found that obesity increases the risk of developing a number of cancers, including breast, womb and prostate cancer.
Professor Jane Wardle, the director of Cancer Research UK's health behaviour unit, said that being overweight or obese upsets the metabolic environment and accelerates cell damage as well as the fat secreting hormones that could trigger tumours.
The new study by Cancer Research has found that the number of men and women under the age of 45 who are morbidly obese has doubled in the past decade. Therefore the obesity epidemic means more people are at risk of developing cancer.
The number of men classed as obese rose from 13.4 per cent to 22.7 per cent, while the level of obese women increased from 15.8 per cent to 22.4 per cent. Men's waist circumference expanded by 1.37in (3.48cms) and women's by 1.71in (4.35cms).
The study also looked at a person's Body Mass Index (BMI), which is calculated by dividing weight in kilograms by the square of a person's height in metres. To be considered morbidly obese, a person must have a BMI of 35 or more. Between 1994 and 2004, the number of women with a BMI of more than 40 doubled.
The findings of the research showed that 12,000 cases of cancer could be prevented each year if a person's BMI did not exceed 25 - classed as overweight.
A more sedentary lifestyle like sitting at a computer takeaway meals and snacking were all contributory factors to the problem.
Wardle said two cancers that claimed most lives in Britain are breast and colorectal and were among those that had been associated with obesity.
"We are seeing evidence of a rise in the number of cancers that can be caused by obesity just when we are seeing a reduction in those caused by smoking," she said.
Obese people are at a greater risk of getting cancers of the womb, gall bladder and kidney and could also increase the risk of prostate and pancreatic cancers.
"The biological link between obesity and cancer is complicated but maintaining a healthy body weight will reduce cancer risk," Wardle said.
"We need to continue raising awareness of the dangers of obesity and offer information to help people lose those extra pounds," she added.
"This research adds to the evidence that the UK is in the grip of an obesity epidemic," Dr Lesley Walker, of Cancer Research UK, said.
"We know that high body weight increases the risk of a number of cancers and it is important we get this message to as many people as possible. A healthy diet with plenty of fibre, fruit and vegetables as well as regular exercise can help people to lose weight and reduce their risk of cancer," Walker added.