Why do women in western countries suffer a higher risk of breast cancer than women from Asia? Some studies suggest it is what they eat. The current issue of the Journal of the National Cancer Institute takes a look at soy, a dietary staple in Asia that is less widely consumed in the West.

Georgetown University oncologist Leena Clarke

Georgetown University oncologist Leena Clarke is co-author of a major analysis of previous studies that looked at soy exposure and breast cancer risk. "We found that there was a small reduction in risk for pre-menopausal women among those women who consumed soy."

Clarke says while soy foods may lower cancer risk, soy supplements don't provide the same health benefit. Soy supplements contain high levels of isoflavones, natural compounds which can mimic the properties of a woman's estrogen hormone and are known to make breast cancer tumors grow. "So, it is not a good idea to consume supplements if you want to avoid estrogenic exposures. However when these phytochemicals [plant compounds that promote health and decrease risk of disease] are consumed in the context of normal food, there are other ingredients in the food that seem to be balancing these estrogenic effects of the phytochemicals," Clarke says. "People have been trying to figure out what it is in soya foods that might be protective if it is not the phytochemicals, and nobody knows."

Clarke says overall health benefits of a diet rich in soy - modest though they may be - likely outweigh any risks for the population as a whole.