Following a diet high in fibre, particularly from whole grains and cereals like brown rice and oats, is linked to a lower risk of colorectal cancer, according to researchers in Britain and The Netherlands who pooled all available published evidence, covering nearly 2 million people. They write about their findings in a study published online in the BMJ on 10 November.

For every additional 10g of fibre in the diet, there was a 10% reduction in risk of colorectal cancer, said researchers from Imperial College London, the University of Leeds, and Wageningen University and Research Centre.

Research has already established a clear link between reduced risk of cardiovascular disease and eating fibre and whole grains. But links between reduced colorectal cancer risk and fibre and whole grains remain somewhat unclear, and studies have shown inconsistent results, despite the suggestion having been around for the best part of 40 years.

For this study, the researchers analyzed the results of 25 prospective studies involving nearly 2 million participants. To reduce any bias, they took into account the design and quality of the studies. The type of analysis they performed is known as a “meta- analysis”, which is a way of pooling results from several studies and treating them as if they came from one large study.

They found that although the overall reductions in colorectal cancer risk were not large, there was a clear, gradual and positive “dose-response” relationship with amount of fibre consumed.

They ranked the participants according to how much daily fibre they ate and found that compared to those with the lowest intake, each 10g a day increase in total dietary fibre was linked to a 10% reduction in risk of colorectal cancer. There was a similarly sized link with cereal fibre.

They also looked at whole grains on their own and found that adding three servings (90g a day) of this food in the diet was linked to around 20% reduced risk of colorectal cancer.

Whole grain foods include oatmeal, porridge, brown rice and whole grain breads and cereals.

Whole grains and cereals are not the only source of fibre in the diet: vegetables and fruit also contain fibre, but the researchers found no link between fibre intake from these foods and risk of colorectal cancer.

But they said that a previous analysis had shown a link between eating large amounts of fruit and vegetables and reduced colorectal cancer risk, suggesting something other than fibre might be responsible for such an effect in these foods.

Since eating more dietary fibre and whole grains is also likely to reduce people’s risk of cardiovascular disease, developing type 2 diabetes, becoming overweight and obese, and possibly also, early death, there are numerous health benefits to doing so, said the researchers. One way to do this is to replace foods made with refined grains with those made with whole grains.

The researchers conclude that:

“… our meta-analysis suggests that a high intake of dietary fibre, particularly from cereal and whole grains, is associated with a reduced risk of colorectal cancer.”

They suggest further studies be done to examine links between different types of dietary fibre and specific sites of cancer in the rectum and colon, for people with varying lifestyles and diets.

They also recommend researchers report more details when they publish studies in this area so that they can be included in future pooled analyses.

In an accompanying editorial, Professor Anne Tjønneland from the Danish Cancer Society, writes that while this analysis adds to the growing evidence on the many health effects of whole grains, we still need to find out what the underlying biological mechanisms might be. She also recommends more studies to investigate the barriers to increasing our dietary intake of whole grains.

Written by Catharine Paddock PhD