Bowel cancer is a big killer
Doubling fibre intake almost halves the risk of developing bowel cancer, research suggests.
The conclusion comes from the biggest study ever undertaken into European eating habits.
Similar findings have been produced in a separate new study by a US team.
However, a third new study - also by US researchers - found little evidence that fibre offers a protective effect.
The European study was funded by a consortium including Cancer Research UK, the Medical Research Council (MRC) and the European Commission.
Scientists studied the diets of more than 500,000 people in 10 European countries.
They found people who ate the most fibre rich food had the lowest incidence of bowel cancer, while those with least fibre in their diets had the most cases of the disease.
A fibre rich diet was defined as 35g a day. That equates to seven portions of fruit and vegetables per day plus five slices of wholemeal bread.
Fibre is found in high quantity in cereals, vegetables and fruit. The research did not examine the effect of fibre supplements or foods with added fibre.
Lead researcher Professor Nick Day said: "Our report suggests that if people with a low level of fibre in their diet were to double their intake that the risk of bowel cancer could be reduced by 40%.
Fruit is a good source of fibre
Dr Elio Riboli, of the International Agency for Research on Cancer, coordinated the study.
He said: "By studying so many different populations with different diets we were able to get a much more accurate picture of how different kinds of foods contributing fibre to our usual diet relate to the incidence of bowel cancer."
The research found that cereals were the main source of fibre in Netherlands, Germany, Sweden and Denmark.
Vegetables were the main source of fibre in France and the UK, while it was fruit in Italy and Spain.
US researchers from the National Cancer Institute, Rockville, found that people who ate a high fibre diet were less likely to develop colorectal polyps, which can lead to bowel cancer.
However, a separate team from National Cancer Institute, who examined 45,000 women over three decades, failed to produce similar evidence.
The European team has suggested that studies which do not show a protective effect from eating fibre may be sampling people whose fibre intake is not sufficiently high to produce a positive effect.
Bowel cancer is the second highest cause of cancer death in the UK responsible for 16,170 deaths each year.
Both studies suggesting a positive effect are published in The Lancet. The negative study is published in the International Journal of Epidemiology.