Soy foods are considered among the healthiest for human consumption, but their estrogen-like properties – found in isoflavones – previously raised concerns of a potential increase in the risk of breast cancer.
But, the new findings showed soy foods not only prevent breast cancer but also benefit women who have breast cancer.
Women with breast cancer who consumed high amounts of isoflavones had a 21 per cent lower risk of dying than women who consumed low amounts.
"Our findings suggest that survival may be better in patients with a higher consumption of isoflavones," said Esther John from the Cancer Prevention Institute of California – a US-based non-profit organisation.
Further, the effect was largely confined to women with hormone receptor-negative tumours and women who were not treated with anti-estrogen therapy such as tamoxifen – which blocks the effects of estrogen, the researchers said, in the paper published in the journal CANCER.
"For women with hormone receptor-negative breast cancer, soy food products may potentially have a protective effect. Women who did not receive endocrine therapy as a treatment for their breast cancer had a weaker, but still statistically significant, association," added Fang Fang Zhang from the Tufts University in Massachusetts, US.
For the study, the team looked at the relationship between dietary intake of isoflavones and death from any cause in 6235 American and Canadian women diagnosed with breast cancer.