There is no convincing evidence that eating more fruit and vegetables can reduce chances of developing cancer, although they are important for maintaining a healthy diet.
That's the conclusion of a review by an Oxford University scientist that looked at a decade of evidence on the links between fruit and vegetables and the development of cancer.
The study, published in the British Journal of Cancer, found that the only diet-related factors that definitely affect cancer risk are obesity and alcohol. Tobacco is still the single biggest cause of cancer.
Professor Tim Key of the Cancer Epidemiology Unit at Oxford University says that while there are undoubted benefits in eating fruit and vegetables, there is little hard evidence that they protect against cancer. But the evidence is indisputable that cancer is strongly linked to being overweight or obese and drinking more alcohol than the recommended daily limits.
He said: 'Fruit and vegetables are an important part of a healthy diet and a good source of nutrients. But so far the data does not prove that eating increased amounts of fruit and vegetables offers much protection against cancer.
'But there's strong scientific evidence to show that, after smoking, being overweight and alcohol are two of the biggest cancer risks.'
Overweight people produce higher levels of certain hormones than people of a healthy weight and this can contribute to an increased risk of breast cancer.
Being overweight can increase your risk of other common cancers like bowel, and also hard-to-treat forms of the disease like pancreatic, oesophageal and kidney cancer.
When alcohol is broken down by the body it produces a chemical which can damage cells increasing the risk of mouth, throat, breast, bowel and liver cancers.
Sara Hiom, director of health information at Cancer Research UK, said: 'Too few people know about the significant cancer risks associated with obesity and drinking too much alcohol. While stopping smoking remains the best way to cut your chances of developing cancer, the importance of keeping a healthy weight and cutting down on alcohol shouldn't be overlooked.
'Keeping alcohol intake to a maximum of one small drink a day for women and two small drinks per day for men and keeping weight within the healthy limits can have an enormous impact.'
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