Recent research has highlighted the role played by lifestyle in the risk of developing breast cancer in women. In particular, certain dietary factors are associated with the disease, which suggests that environmental factors play a considerable role in the aetiology of the disease. Case control studies are prone to recall errors by subjects, but allowing for this factor, meta-analysis of such studies show a 15% reduction in breast cancer cases with a 20g/d intake of fibre. In fact, the errors associated with case-control studies may explain the inconclusive results seen when considering the protective effects of dietary fibre on breast cancer. However, meta-analysis of prospective cohort studies supports these findings and show beneficial effects of higher intakes of dietary fibre on breast cancer risk1. The authors of this study used relevant studies through to January 2011 and reported an inverse association between dietary fibre and breast cancer.
The results included 10 prospective cohort studies of dietary fibre with regard the risk of breast cancer that included a total of 712,195 subjects and 16,484 cases of breast cancer. Comparison of the highest with the lowest dietary fibre intake resulted in a relative risk of 0.89. The inverse association between dietary fibre and breast cancer was geographically uniform, showed little evidence of heterogeneity, and the menopausal status of the subjects did not alter the results. The fact that omission of individual studies did not significantly alter the results, suggested that there was good agreement between the data from different research groups. When the data was analysed to assess the effect of varying fibre intake on breast cancer risk, it was estimated that for every 10g/d increase in fibre, a 7% decrease in the risk of breast cancer was possible.
Researchers have suggested several mechanisms by which dietary fibre might be inversely associated with breast cancer risk. It is known that fibre is able to control insulin resistance in diabetics and those with metabolic syndrome, possibly due to improvements in the glycaemic response to foods. Because insulin resistance is hypothesised to play a role in the development of breast cancer, fibre may be protective via improvements in insulin sensitivity. In addition, fibre may inhibit colonic bacterial β-glucuronidase activity. This enzyme can deconjugate excreted oestrogen and thereby allow increased reabsorption from the colon. By inhibiting its activity, fibre can increase the excretion of conjugated oestrogen in the faeces and lower circulating levels. Fibre is also associated with increased plant and whole grain intakes, and this would suggest a greater intake of both micronutrients and plant phenolics, both of which may explain the reduction in cancer risk.
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