Dr Tim Key, of the University of Oxford, told a cancer conference that
scientists are still discovering how certain foods contribute to cancer but they
know that diet, alcohol and obesity play a major role.
"Five percent of cancers could be avoided if nobody was obese," he said.
While tobacco is linked to about 30 percent of cancer cases, diet is involved
in an estimated 25 percent and alcohol in about six percent.
"We know that obesity and alcohol are important," said Key.
Obesity raises the risk of breast, womb, bowel and kidney cancer while
alcohol is known to cause cancers of the mouth, throat and liver. Its dangerous
impact is increased when combined with smoking.
Both alcohol consumption and obesity rates are rising in many countries.
Key told the meeting of the charity Cancer Research UK that other elements of
diet linked to cancer are still unknown but scientists are hoping that the EPIC
study, which is comparing the diets of 500,000 people in 10 countries and their
risk of cancer, will provide some answers.
Early results of the study have revealed that Norway, Sweden and Denmark have
the lowest consumption of fruit and vegetables among European countries while
Italy and Spain have the highest. Eating at least five portions of fruit and
vegetables a day is recommended to reduce the risk of cancer.
Key, principal scientist on the EPIC study, said it is looking at dietary
links to some of the most common cancers including colorectal, breast and
prostate.
So far it has shown that obesity is linked to an increased risk of colorectal
cancer, while processed and red meat also probably raise the chances of
developing the disease and eating lots of fruit and vegetables decrease the
odds.
"Hormones are the key factor in breast cancer. There is currently about a
five-fold variation in breast cancer rates around the world. Much of that
variation is due to parity, the number of children (a woman has) and breast
feeding," Key said.
But he added that obesity and alcohol can also raise the risk of the disease.
Scientists working on the study have not positively identified any dietary
factors associated with prostate cancer.
