Soy and Hormone Related Cancers
Are soy foods safe for women with a history of hormone-related cancers, including estrogen receptor positive breast cancer, uterine (endometrial) cancer, or ovarian cancer?
Summary: The current consensus among health experts who study soy is that breast cancer survivors can safely eat these foods. Some studies suggest soy is protective against breast cancer recurrence. See our information on Soy and Breast Cancer, for additional information.
There is less research regarding soy and other hormone related cancers, including endometrial and ovarian cancers. However, the studies that are available suggest that soy foods are safe for women with a history of endometrial or ovarian cancer.
Confusion about soy arises from the term "phytoestrogens." Some soy nutrients—the isoflavones—have chemical structures that look a bit like the estrogen found in a woman's body. This is where the term phytoestrogen originated. However, phytoestrogens are not the same thing as female estrogens. Soy foods do not contain estrogen.
Soy and Endometrial Cancer
Several large, human studies, following thousands of women for many years, consistently suggest soy protects against endometrial cancer. Compared with women who do not eat soy, women who regularly eat soy tend to have lower endometrial cancer risk.
In these studies, women eating the most soy typically eat around one to three servings of soy foods, such as tofu or soy milk, per day.
All of these studies are observational. This means researchers collect diet information from women, then follow them for many years to see who develops endometrial cancer. In an observational study, it is always possible that the true connection between lower endometrial cancer risk and soy foods is due to something else that is related to eating soy.
For example, women who eat soy foods also may eat more vegetables. They may exercise more and maintain a healthier body weight. Any one of these other things could be the reason why soy-eating women have lower endometrial cancer risk.
This means observational studies can't conclusively prove that soy protects against endometrial cancer. However, these studies are reassuring in affirming that soy foods do not increase endometrial cancer risk.
These studies have not considered soy and endometrial cancer recurrence. However, there is no reason to believe that soy would reduce risk of developing endometrial cancer the first time, but increase risk of recurrence, or getting it again.
Soy and Ovarian Cancer
The picture with soy and ovarian cancer is similar to endometrial cancer. There are large, multi-year studies of soy food consumption and risk of ovarian cancer, but these studies are observational.
Some of the study results suggest soy protects against ovarian cancer. Other studies show no reduced risk of ovarian cancer in women who eat the most soy. These studies do not suggest that soy increases ovarian cancer risk
Because the soy and ovarian cancer studies are observational, they cannot prove cause and effect. However, the research is reassuring in affirming that soy foods do not increase ovarian cancer risk.
As with endometrial cancer, these ovarian cancer studies have not considered soy foods and risk of ovarian cancer recurrence. However, there is no reason to believe that soy foods would have a different effect on risk of developing ovarian cancer the first time, than on risk of recurrence, or getting cancer again.
Soy foods are a healthy option, while soy dietary supplements may not be. The research on soy and endometrial and ovarian cancers has considered soy foods, not soy dietary supplements. If you require extra calories during cancer treatment from a medical food supplement, the soy protein in this type of product is not a problem. However, soy pills and isoflavone-enriched powders should be avoided.
If you're a woman concerned about reproductive health and you like soy, stick to healthy, whole soy foods, such as tofu, tempeh, soymilk, and edamame. The occasional soy protein bar or snack food is fine, but as with all plant foods, less processed is better.
Stop Soy Fear
In the end, feel confident in whatever choice you make about soy foods. Eat these foods if you enjoy them, or skip them altogether if soy isn't to your liking.
The original question and answer were generously donated by Diana Dyer, MS, RD a cancer survivor, registered dietitian, organic garlic farmer, and the author of "A Dietitian's Cancer Story: Information & Inspiration for Recovery & Healing from a 3-time Cancer Survivor.
Question and Answer updated by Suzanne Dixon, MPH, MS, RD, on behalf on the ON DPG
References and Resources
- Ollberding NJ, Lim U, Wilkens LR, Setiawan VW, Shvetsov YB, Henderson BE, Kolonel LN, Goodman MT. Legume, soy, tofu, and isoflavone intake and endometrial cancer risk in postmenopausal women in the multiethnic cohort study. J Natl Cancer Inst. 2012;104(1):67-76.
- Myung SK, Ju W, Choi HJ, Kim SC; Korean Meta-Analysis (KORMA) Study Group. Soy intake and risk of endocrine-related gynaecological cancer: a meta-analysis. BJOG. 2009;116(13):1697-705.
- Bandera EV, King M, Chandran U, Paddock LE, Rodriguez-Rodriguez L, Olson SH. Phytoestrogen consumption from foods and supplements and epithelial ovarian cancer risk: a population-based case control study. BMC Womens Health. 2011;11:40.
- Hedelin M, Löf M, Andersson TM, Adlercreutz H, Weiderpass E. Dietary phytoestrogens and the risk of ovarian cancer in the women's lifestyle and health cohort study. Cancer Epidemiol Biomarkers Prev. 2011;20(2):308-17.
- ACS Guidelines on Nutrition and Physical Activity for Cancer Prevention.
- American Institute for Cancer Research, Soy Update.
Page Updated: April 2013