Soy milk, tofu and other soy products contain phytoestrogens, chemicals that can mimic the behaviour of the hormone estrogen. Because estrogen fuels many breast cancers, soy has long been a source of concern: Can it heighten the risk of breast cancer or raise the odds of recurrence?
In the lab, phytoestrogens can stimulate the growth of breast cancer cells. But in human studies, scientists have not found that diets high in soy increase breast cancer risk. In fact, most have found the reverse.
In a report in The Journal of the American Medical Association in 2009, scientists who looked at 5,042 people in the Shanghai Breast Cancer Survival Study found that soy was linked to a significantly lower risk of breast cancer recurrence and mortality. But the study, while encouraging, was carried out in China, so questions lingered about the extent to which the findings applied to women elsewhere.
In a more recent multi-year study, published in May, 2012 in The American Journal of Clinical Nutrition, scientists followed nearly 10,000 breast cancer survivors, many of them in the United States. They found that women who ate the most soy had lower rates of cancer recurrence and mortality.
Though the findings reflect only a correlation, they suggest that the concerns about soy and breast cancer may be unfounded.
The verdict
Despite concerns about its phytoestrogen content, eating soy has not been shown to promote breast cancer.
In the lab, phytoestrogens can stimulate the growth of breast cancer cells. But in human studies, scientists have not found that diets high in soy increase breast cancer risk. In fact, most have found the reverse.
In a report in The Journal of the American Medical Association in 2009, scientists who looked at 5,042 people in the Shanghai Breast Cancer Survival Study found that soy was linked to a significantly lower risk of breast cancer recurrence and mortality. But the study, while encouraging, was carried out in China, so questions lingered about the extent to which the findings applied to women elsewhere.
In a more recent multi-year study, published in May, 2012 in The American Journal of Clinical Nutrition, scientists followed nearly 10,000 breast cancer survivors, many of them in the United States. They found that women who ate the most soy had lower rates of cancer recurrence and mortality.
Though the findings reflect only a correlation, they suggest that the concerns about soy and breast cancer may be unfounded.
The verdict
Despite concerns about its phytoestrogen content, eating soy has not been shown to promote breast cancer.