Soaring obesity levels could result in up to 12,000 cases of weight-related cancer being diagnosed annually in the UK by 2010, say experts.
Obesity is linked to several cancers
The Department of Health predicts a 14% increase in obesity by 2010, which will mean 27.6 million people in the UK will be classified as obese.
Cancer Research UK has calculated that this will lead to around 1,500 extra weight-related cancers a year.
Researchers have estimated that excess weight causes 3.8% of cancers.
The most recent figures show that in 2003 there were 24.2 million obese or overweight people in the UK.
The projected rise means that weight-related cancers are likely to rise from 10,500 cases per year to 12,000 in just seven years.
After smoking obesity is one of the most important preventable causes of cancer.
Lack of awareness
But few people are aware that being overweight or obese increases the risk of developing the disease.
A Cancer Research UK survey found that only 29% of overweight or obese people were aware of the cancer connection.
Professor Tim Key, an expert on diet and cancer, said: "It is now well established that being overweight increases the risk of developing several types of cancer.
"The effects on breast and womb cancer are almost certainly due to the increased production of the hormone oestrogen in the fatty tissue.
"We are less sure of the precise mechanisms in other obesity related cancers but we can confidently predict that the number of these cases will increase unless the rise in obesity in Britain can be reversed."
Research in the US has found that among men and women who have never smoked the risk of overall cancer death is increased by up to a third in obese people.
Cancer Research UK is calling for a comprehensive strategy to halt the rise in obesity in the UK, which must be particularly targeted at children and young adults.
Women who are overweight or obese are at increased risk of womb cancer and postmenopausal women have a greater risk of developing breast cancer.
There is also evidence for a link between obesity and cancers of the bowel and kidney.
Obese people who develop cancer are also less likely to survive than those with a healthy weight, possibly because the cancer is more difficult to diagnose and is therefore not treated until it is more advanced.
Dr Lesley Walker, the charity's director of cancer information, said: "Eating healthily and exercising regularly is the best way to maintain a healthy body weight and to reduce your cancer risk."
In the UK 23% of men and 25% of women are now classified as obese.
The numbers of obese children have almost tripled in the past 20 years, with more than 5% now obese and more than 20% overweight.