The Concern about Soy Products
Soy isoflavones may have estrogen-like properties. This has raised concerns regarding soy food consumption among well women and also breast cancer survivors.
In 2008, the Singapore Chinese Health Study (SCHS) was published. In this study, 35,303 women who were well, aged 45 to 74 years, were followed up at least for 5 years for occurrence of breast cancer. During follow-up, it was noted that post-menopausal women who consumed more soy products (10.6mg isoflavones per 1000 Kcal) had lower occurrence of breast cancer compared to women who consumed less soy products. There was no difference in pre-menopausal women. A similar finding was reported by the Japan Public Health Center-Based Prospective Study (JPHC) in 2003.
The After Breast Cancer Pooling Project (ABCPP) included data of 18,000 breast cancer survivors from the US and China. Only 10% of women in the US studies consumed soy food daily (≥10 mg isoflavones per day) whereas 90% of Chinese women consumed soy food daily. With an average follow-up of over 7 years, the risk of breast cancer recurring was reduced by 36% in women who consumed the most soy products compared to women who consumed the least. This was seen in American as well as Chinese women.
Chi’s group from Shenyang pooled data from 11,000 breast cancer survivors. Again, soy food intake after breast cancer diagnosis was associated with 21% less breast cancer recurrence. This was seen in estrogen receptor positive and negative cancers, and in women who were pre or post menopause.