From The New York Times:
The diet messages are everywhere: the National Cancer Institute has an “Eat 5 to 9 a Day for Better Health” program, the numbers referring to servings of fruits and vegetables, and the Prostate Cancer Foundation has a detailed anticancer diet. Yet despite the often adamant advice, scientists say they really do not know whether dietary changes will make a difference. And there lies a quandary for today’s medicine. It is turning out to be much more difficult than anyone expected to discover if diet affects cancer risk. Hypotheses abound, but convincing evidence remains elusive.
So should people who are worried about cancer be told to follow these guidelines anyway, because they may work and will probably not hurt? Or should the people be told that the evidence just is not there, so they should not deceive themselves?
More here.