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K E Y P O I N T S

Bowel cancer (also known as colorectal cancer) mostly affects people in their 60s and 70s, but younger people can get it too.

Two large-scale studies - one involving more than 500,000 people - looked at the association between diet and bowel cancer.

Both studies found a link between high-fibre diet and low bowel cancer risk. In the largest study, consuming 35g of fibre daily reduced the risk by up to 40 per cent.

The effects of eating fibre have been widely debated, but based on the new research, most experts agree it does seem to be beneficial for reducing bowel cancer risk.

The minimum recommended level of fibre intake is 18g per day, but many people currently only eat 12g.

Fibre lowers bowel cancer risk

Bupa investigative news - 12 May 2003
written by Rachel Newcombe, reporter for Bupa's Health Information Team

Cancer of the bowel is the second highest cause of cancer death in the UK, responsible for 16,170 deaths each year. Lifestyle and dietary habits are known to play a part and new research has added weight to the theory that a high-fibre diet can reduce one's risk of developing bowel cancer. So, what were the study findings, how much fibre is needed to produce the most benefit and what else can we do to reduce the risks of this disease?

What were the headlines?

News of the benefits of fibre was featured in a range of newspapers worldwide, gaining headlines such as "Fibre slashes cancer risk", "Huge study backs fibre in cancer risk debate", "Diet high in fibre shown to cut bowel cancer risk", and "Fibre benefit found".

Some of the reports focused purely on one of the studies - most notably the European one - while others looked at the merits of both.

What is the bigger picture?

The two studies were published in The Lancet medical journal. The first was led by Ulrike Peters from the National Cancer Institute in America. It looked at the relationship between fibre intake and the presence of polyps (also known as adenomas) in the bowel area. These are benign (non-cancerous) tumours that can lead to the development of bowel cancer. The study was conducted within the Prostrate, Lung, Colorectal and Ovarian (PLCO) Cancer Screening Trial.

"We studied these benign tumours because they're known to be an early step towards cancer of the colon," explained Dr. Ulrike Peters. "Prevention of colon tumours at this early stage should reduce the risk of life-threatening cancers."

The fibre intake of nearly 34,000 participants without polyps and almost 3,600 people with at least one bowel adenoma were compared. They discovered that a high intake of dietary fibre was associated with a lower risk of adenoma. Participants in the top 20 per cent for dietary fibre had a 27 per cent lower risk of adenoma than people in the bottom 20 per cent (representing an increase in fibre intake of 24g per day). The association was strongest for fibre from grains, cereals and fruits.

Dr Peters explained: "Fibre from vegetables did not seem to offer any protection, but we are not sure why there should be such a difference. Our study, as well as the EPIC study, suggests that it has been premature to dismiss a role for dietary fibre in the prevention of colorectal cancer."

The second study was conducted in Europe, involving researchers from Cancer Research UK, the Medical Research Council (MRC), the International Agency for Research on Cancer (IARC), and the European Prospective Investigation into Cancer and Nutrition (EPIC) consortium.

More than half a million people aged between 25 and 70 years old were recruited from 10 European countries. They each completed a dietary questionnaire in 1992-98 and were followed up, on average after 4.5 years, to discover if cancer had developed. The researchers found that people in the top 20 per cent for fibre intake, who ate an average of 35g of fibre daily, had the risk of colorectal cancer reduced by 40 per cent, compared to those eating 15g of fibre daily.

Dr. Elio Riboli, from IARC, believes the involvement of 10 countries helped considerably. "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," he said.

Professor Nick Day said, "It became clear that the amount of dietary fibre in food was inversely related to bowel cancer incidence. Our report suggests that if people with a low level of fibre in their diet were to double their intake, the risk of bowel cancer could be reduced by 40 per cent."

Describing the amount of fibre consumed, Dr Sheila Bingham from the MRC said, "People with the most reduction were eating seven portions of fruit and vegetables per day, similar to the amount eaten by Mediterranean populations, and the equivalent of five slices of wholemeal bread."

“This study strengthens the argument that dietary fibre intake may be important to reduce the risk of colorectal cancer. What we don't yet know is whether this is a causal or coincidental association. In other words, does the fibre itself cause the reduction in risk or it is simply that high fibre intake is the sign of a diet that is high in fruit, vegetables and whole grains? If it is the latter, then the lowered risk could actually be due to other substances that are present in these foods.”

“Either way, the advice for a healthy diet remains the same: eat a varied diet containing plenty of fruit, vegetables and wholegrain foods, and less saturated fat, salt and sugar.”

Dr Annabel Bentley,
assistant medical director, Bupa Group

What does this mean?

Professor Robert Souhami, director of clinical research at Cancer Research UK, welcomed the news. "The public can place great reliance on the results of such a large survey which has taken place in so many countries with widely differing levels of fibre in their diet. The results of the EPIC study underline the importance of including plenty of fibre in our daily diet to reduce the risk of bowel cancer," he said.

Professor R. J. C. Steele, a medical expert at Colon Cancer Concern, said, "The two studies add considerable strength to the theory that dietary fibre is protective against colorectal cancer."

Dr. Hannah Theobald, a nutrition scientist from the British Nutrition Foundation, said, "Both of these studies are epidemiological, looking back in time at the incidence of cancers and the intake of fibre at a baseline. Their strength is that they both use very large numbers, and EPIC is based across the whole of Europe. Together they strengthen the argument that fibre may help prevent cancer."

However, she also added that it might not necessarily mean that fibre itself is causing the effect - it could be another component within the foods consumed. "It may well be that fibre acts as a marker for the intake of plant foods," she explained. "There are many thousands of bioactive components in plant foods, and there are a range of components that may protect against cancer, including polyphenols such as flavonoids, lignans and anthocyanins."

A C T I O N P O I N T S

Be aware of bowel cancer and look out for the possible signs and symptoms, such as a change in bowel habit, bleeding, stomach pain and anaemia. Other risk factors include ulcerative colitis and a family history of bowel cancer.

Eat a healthy diet including at least 18g of fibre.

Good sources of fibre include - brown rice and pasta, wholemeal bread, breakfast cereals, beans and pulses, dark green vegetables and fruits such as berries.

Take up bowel screening when it becomes available.

What does this mean to me?

"People should try to adhere to the five a day message, of five portions of fruit and vegetables per day," suggested Professor Steele. "In addition, they should attempt to increase dietary fibre in the form of cereals and brown - preferably wholemeal - bread."

The recommended intake of fibre per day for adults is 18g - nearly half that of the 35g a day found to be most beneficial by researchers. However, according to Dr. Theobald, many people aren't even eating the current suggested level. "The average UK intake is 12g per day, which falls short of the recommended amount," she said.

If you're about to start eating more fibre, "it's best to increase the amount gradually, so that the gut and bacteria can adjust," advised Dr. Theobald. "Make sure that you drink a lot of fluids too, as fibre holds water."

Other lifestyle approaches, such as exercising regularly, not smoking and avoiding obesity are beneficial, said Professor Steele. He also suggests that, "accepting invitations to be screened when the national programme starts," would be advisable.

Being aware of bowel cancer and knowing the symptoms can help speed up diagnosis. The main things to look for, said Professor Steele, are, "persistent changes in bowel habits and rectal bleeding," and Beating Bowel Cancer recommend getting into the habit of looking in the toilet after using it to spot changes.

Summary

The role of fibre in bowel cancer has been debated over the years, but these two studies appear to show an association. As fibre intake is one factor that can be controlled by individuals, it seems practical to consider eating more if it will offer some degree of cancer protection.