While soy is widely known to be a positive dietary alternative to animal protein, reports in the news media have led many of my patients to fear that "plant estrogens", such as those found in soy foods, will cause breast cancer, or can be harmful to breast cancer patients.
However, what is not widely known by the public is that the type of phytoestrogen that soy is rich in is called isoflavones,which actually may help protect against breast cancer.
New evidence from a December 2009 study in the Journal of the American Medical Association, the most widely-circulated medical journal in the world, supports the idea that soy is beneficial to women concerned about breast cancer.
This large, long-term study examined 5,042 Chinese women who were breast cancer survivors from 20 to 75 years of age. They were followed between 2002 and 2009. It was found that those who ate the most soy food had the lowest rates of death and cancer recurrance. This was true for both estrogen receptor-positive and estrogen receptor-negative forms of cancer.
The study also found that eating soy did not interfere with the beneficial effects of the anti-cancer drug tamoxifen in those who were taking it. The positive effect of soy increased until a limit of 11 grams per day was reached. After that point, more soy did not provide additional benefit.
The authors of the study were quoted to say "we found that soy food intake is safe and was associated with lower mortality and recurrence among breast cancer patients,"…."This study suggests that moderate soy food intake is safe and potentially beneficial for women with breast cancer."
In an editorial written by Rachel Ballard-Barbash, MD, MPH, from the National Cancer Institute in Bethesda, Maryland, and Marian L. Neuhouser, PhD, from the Fred Hutchinson Cancer Research Center in Seattle, which accompanied the study, the authors concluded that “clinicians can advise their patients with breast cancer that soy foods are safe to eat and that these foods may offer some protective benefit for long-term health.”
I’m happy to share this information with my patients who may be avoiding soy for this reason, and therefore missing out on its many other benefits in a healthy diet.