Breast cancer is the most common cancer for women globally.  Despite common misconception and theoretical concerns for isoflavone’s potential to increase breast cancer risk, numerous large cohort studies and meta-analysis have confirmed the safety of consuming 1-2 soya servings daily.  The American Institute of Cancer Research (AICR)¹ and World Cancer Research Fund (WCRF) UK² have also confirmed the safety of soya isoflavones and consumption of soya foods with regard to breast cancer risk and for breast cancer patients.  The AICR and WCRF have also stated that limited data indicates that consuming soya foods may potentially reduce risk and recurrence of breast cancer.  

Boutas and colleagues wanted to identify the quantity of soya isoflavones needed to provide protection in both pre- and post-menopausal women.

The meta-analysis used data from eight prospective studies which provided adequate data on quantities of soya consumed and incidence of breast cancer risk.

Intakes of soya were extrapolated into two categories:

• Low intakes at 0-15mg isoflavones daily
• High intakes at >15mg soya isoflavones daily

15mg isoflavones is equivalent to a small serving (150ml) of soya drink or a small pot of soya alternative to yogurt, 35g tofu or 25g soya mince.

Data from 7 out of the 8 selected studies was extract data for women who were diagnosed with breast cancer.  A total of 9,699 breast cancer incidences were reported.  Of these cases, 75% consumed 0-15mg isoflavones daily and only 25% reported consuming adequate high levels of soya (i.e., >15mg isoflavones daily) p<0.00001.

A further meta-analysis was undertaken on four of the eight studies which provided adequate data to analyse correlation between isoflavones and breast cancer risk.  These studies adjusted for other potential risk factors e.g., body weight, smoking, age, menopausal status etc. 477,832 participants took part in the four studies and a total of 8,271 breast diagnosis reported (1.7% prevalence).  Once again, soya isoflavone intakes were found to be inversely correlated with breast cancer risk. The low soya consumers showed a four-fold increased breast cancer risk compared to higher soya consumers, p<0.00001).  

• 6,555 cases of breast cancer consumed 0-15mg isoflavones daily (79% of all cases, 1.37% of total participants)
• 1,716 cases consumed >15mg isoflavones daily (21% of all cancer cases & 0.35% of all participants)

Both pre- and post-menopausal women can potentially reduce their breast cancer risk by consuming soya daily

Five out of the eight selected studies provided menopausal status data.  The majority of cancer cases (77%) were low soya consumers, p<0.0001 for both pre- and post-menopausal women.

This is yet another meta-analysis with a total of almost half a million subjects demonstrating a clear trend for lower breast cancer incidence for those consuming at least a small serving of soya foods or drinks daily.