Can high fibre reduce breast cancer?

A high-fibre diet may reduce cancer risk in pre-menopausal women. Sanjay Tanday reports

What is the story?
Pre-menopausal women can reduce their risk of breast cancer by eating more fibre such as wholemeal bread and cereal, according to media reports.

UK researchers found that pre-menopausal women who ate 30g or more of dietary fibre a day halved the risk of breast cancer compared with women who ate less than 20g a day. Eating fibre gave no protection, however, to women who had gone through the menopause.

The researchers suggested three possible causes for the link between a high-fibre diet and a reduced risk of breast cancer in pre-menopausal women.

High-fibre foods are a rich source of vitamins, zinc and other nutrients that have protective anti-oxidant properties.

Secondly, the high intake of fibre may be reducing variations in insulin levels and high levels of insulin are associated as a possible cause of cancer.

In addition, they proposed that dietary fibre might reduce levels of oestrogen, which has been linked to breast cancer.

What is the research?
The reports are based on a UK cohort study that examined the eating patterns of more than 35,000 women, aged between 35 and 69, for seven years.

To investigate the link between dietary fibre and breast cancer, lifestyle factors including smoking, BMI and alcohol intake, were adjusted for.

The sample group included women who were vegetarians, fish but not meat eaters, or meat eaters. The women completed a food frequency questionnaire and fibre intake was calculated. Daily amounts of fibre were then calculated from the frequency of consumption and the nutrient content of the portion sizes.

Of the group, 350 post-menopausal and 257 pre-menopausal women developed breast cancer during the study.

In the study it was found that these women had a greater intake of protein and a lower intake of dietary fibre and vitamin C when compared with the cancer-free women.

In pre-menopausal women, but not post-menopausal women, a diet including 30g or more of fibre reduced the risk of breast cancer by 48 per cent when compared with a diet including less than 20g of fibre.

The researchers thought this was because of the anti-oxidant properties found in high-fibre foods, the lowering of insulin levels or a regulation of oestrogen levels in the body.

What do the researchers say?
Lead researcher Professor Janet Cade, head of nutritional epidemiology at Leeds University, said that previous research had failed to show a link between increased dietary fibre and a lower risk of breast cancer. But those studies had not drawn any distinction between pre- and post-menopausal women.

‘Our study found no protective effect in the older group, but significant evidence of a link in the pre-menopausal women.

‘We don't yet know at which point in life dietary habits impact on a woman's susceptibility to breast cancer. The relevant exposure may be earlier in life, explaining why the protective effect was not shown in the post-menopausal group.'

One of the main strengths of this study was that it was designed to look at vegetarians, meat eaters and fish eaters, allowing for a range of exposure to dietary fibre intakes, said Professor Cade.

Further research is needed to identify the reason why a high-fibre diet can cut breast cancer risk, she said.

What other researchers say?
Dr Frankie Phillips, expert in dietetics from the British Dietetic Association, said that although the findings were interesting, they did not demonstrate a causal link.

‘Fibre may have a role to play, but there are a number of other dietary and lifestyle factors that are important when considering breast cancer risk.

‘Clearly more research would be needed to understand the mechanism of this link.'

It is important that when increasing the fibre content of the diet, be sure to drink more fluid and beware of introducing everything at once, she advised.

Anna Wood, policy and campaigns officer for the charity Breast Cancer Care, said: ‘It is important to remember that the risk of breast cancer for women is lower before menopause. Eighty per cent of cases occur in women over the age of 50.'

Informing patients

  • A high-fibre diet can halve the risk of breast cancer in pre-menopausal women.
  • Eating more than 30g a day of fibre is required to halve the risk of breast cancer.
  • Eating a high-fibre diet gave no protection to women who had already gone through the menopause.
  • Fibre could reduce levels of oestrogen, which has been linked to breast cancer
  • Further research is required to identify the reasoning behind the link.

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