Both soy and fava beans contain the compound genistin, which in the past have been found to be able to stimulate the growth of estrogen-positive breast cancer cells, leading doctors to tell women with breast cancer to stay away from soy foods.
However, contradictory studies have shown that women with long-term, high-soy diets have lower breast cancer recurrences. Specifically, Professor Leena Hilakivi-Clarke of Georgetown University found that rats with a long-term high-genistein diet responded better to anti-estrogen treatments than control subjects. In addition, they were less likely to have recurrences of cancer. So long term consumption of genistein, found in soybeans, might actually have a protective effect against breast cancer.
In trying to deal with the contradictory research findings, Hilakivi-Clarke investigated the effect of genistein in rats and found that T-cells of the genistein-fed rats were primed to attack the tumor before they were given anti-cancer drugs. The T-cells responded more quickly and strategically, overcoming certain defense mechanisms cancer cells use to evade attacks.
Hilakivi-Clarke reported, “Results suggest that genistein’s ability to activate anti-tumor immune responses and reduce expression of immunosuppressive mechanisms may explain why lifetime genistein intake reduces risk of breast cancer recurrence.”
“It is critical that genistein is consumed well before a tumor develops to program the tumor to exhibit good immune responses,” added Xiyuan Zhang, a doctoral student on Hilakivi-Clarke’s team.
There is evidence that genistein also has a beneficial effect against other types of cancer, including brain, colon, and for men prostate, for rats that is. However, the fact that humans and rodents metabolize soy differently could account for differences in results.