Researchers at Liverpool University found that a daily serving of broccoli, cabbage, lettuce and sprouts, can reduce the cancer risk by 46%.

Colon cancer is responsible for around 20,000 deaths a year in the UK.

The leafy green vegetables contain fibre rich in the sugar galactose, which scientists believe could help prevent proteins called lectins from binding to the lining of the colon and causing damage.

This study provides important evidence that the association between diet and colon cancer is mediated via specific food components rather than just by a general effect of fibre

Professor Jonathan Rhodes

Diet

The study, sponsored by North West Cancer Research Fund, studied 1,000 people, half of whom had colon cancer.

They quizzed people about their diet and found that those without the colon problems ate more of the vegetables.

Professor Jonathan Rhodes, who led the research said: "The stories about the benefits of a high fibre diet that have been circulating for years have typically oversimplified the situation so it is not surprising that there was confusion and contradictory reports.

"This study provides important evidence that the association between diet and colon cancer is mediated via specific food components rather than just by a general effect of fibre."

The report, published in Gastroenterology, also highlighted the harmful effects of a diet too high in calories and red meat.

It also extolled the positive benefits of regular exercise.