Why green?

The world-first study asked 22 men to eat 400 grams of broccoli a week for a year, in addition to their normal diet.

Tissue samples were taken from their prostate gland before the start of the trial and after six and 12 months, and analysed.

The study found the broccoli had a big effect on the expression of particular genes in the prostate associated with the formation of cancer and inflammation.

The research's leader, Professor Richard Mithen, said other vegetables and fruits also reduced the risk of developing prostate cancer, though probably in different ways.

"Once we understand these, we can provide much better dietary advice on which specific combinations of fruit and vegetable are likely to be particularly beneficial," he said. "Until then, eating two or three portions of cruciferous vegetable per week … should be encouraged."

The research was published in the online PLoS One journal yesterday.