Obesity has become the main cause of cancer in non-smokers, a global conference will hear next week.
The World Cancer Research Fund has spent five years collecting information about the effect bodyweight, diet and physical activity has on the risk of developing cancer and will present its findings in London on Thursday.
Smoking is still the single biggest cause of cancers, accounting for one third of the 300,000 cases in the UK each year.
But only one quarter of people smoke and research has found that for non-smokers being overweight or obese is the most important avoidable cause of cancer. In the UK, 12,000 people a year could avoid cancer if they maintained a healthy weight, according to Cancer Research UK.
Obesity is known to cause between nine and 15 per cent of breast cancers - more than defective genes. A recent study found women who have gone through the menopause and are obese increase their risk of developing breast cancer by a third. Obesity is known to increase the risk of cancer by raising the level of hormones such as oestrogen, which feeds many breast cancers. An obese woman's lifetime risk of developing breast cancer is one in seven compared to one in nine for the general population.
Risk
Obesity is also known to increase the risk of bowel cancer, and accounts for between 11 per cent and 14 per cent of cases annually. Men who are obese have a 60 per cent increased risk of developing the disease.
Studies have also estimated that a quarter of kidney cancers, a third of oesophageal cancers and four in 10 womb cancers are caused by obesity.
There is evidence that obesity is linked to nine other rarer cancers. Professor Tim Key, an epidemiologist at Cancer Research UK who is presenting at the London conference next week, said: "Already the majority of people don't smoke and for them obesity may be the most important identified cause of cancer."
