Eating soy could pose risks to some women who begin consuming it as adults by making breast cancer tumours resistant to treatment, US researchers said.
A study on lab rats showed that those who were fed a soy compound all their lives responded well to a popular breast cancer drug, tamoxifen, but those who began eating it as adults, and after they developed breast cancer, grew resistant.
The research suggests a possible reason why tamoxifen stops working and allows tumours to grow again in some women, said scientists from Georgetown University who presented their findings at a medical conference in Chicago.
"These results suggest that Western women who started soy intake as adults, should stop if diagnosed with breast cancer," said senior author Leena Hilakivi-Clarke, professor of oncology at Georgetown.
Soy renders tamoxifen impotent
Soy contains isoflavones that mimic the oestrogen produced in the body, only at lower levels, and is considered a healthy protein source found in foods like tofu, miso, soy beans and soy milk.
Its potential benefits against breast cancer are often linked to the lower rates of hormone receptor positive types of breast cancer seen in Asian women who live in parts of the world where soy consumption is common.
Since tamoxifen is typically given to breast cancer patients with oestrogen receptor and/or progesterone receptor positive types of tumours, the finding suggests that late-life adoption of a soy diet may have rendered the drug impotent.
The study was presented at the American Association for Cancer Research (AACR) Annual Meeting.
(Sapa, April 2012)
Soy and Health