Soy is often claimed to be bad for endometriosis but is it really? To answer this question, we need to examine the evidence, unfortunately though when it comes to research on endometriosis and diet, the evidence is scarce.

WHY SOY IS THOUGHT TO BE BAD FOR ENDOMETRIOSIS

Endometriosis is an inflammatory disease that is fuelled by estrogen. Soy has mildly estrogenic properties on the body as it contains high quantities of phytoestrogens (plant-based estrogens); these phytoestrogens or isoflavones are structurally similar to estradiol (estrogen) and can bind to estrogen receptors. However, phytoestrogens can also have an anti-estrogenic effect on the body (1).

WHAT IS THE RELATIONSHIP BETWEEN ESTROGEN AND ENDOMETRIOSIS?

Hormones estrogen and progesterone both regulate the growth of the endometrium (the lining of the uterus); both hormones stimulate the growth of the endometrial lining in preparation for conception. If pregnancy doesn’t occur a decrease in progesterone triggers menstruation or shedding of the endometrium. In endometriosis, estrogen and progesterone function is disrupted which can result in progesterone resistance and estrogen dominance (2). This hormone imbalance is believed to cause inflammation and the increased levels of estrogen promote the growth of endometriosis lesions (2).

WHAT DOES THE RESEARCH SAY?

Animal studies have found that early-life consumption of isoflavones results in changes to the uterus and the regulation of the reproductive axis which is responsible for the release of hormones (3). 

A recent animal study showed that rats with endometriosis who were fed a diet of soy, their endometriosis lesions grew faster than the rats who were receiving a soy-free diet (4). 

Rats however, have a very different physiology to humans, so while these results are interesting, we need human studies for the research to be of more relevance.

When it comes to research on humans the studies are limited and the results are mixed:

One population-based study identified an increased risk of endometriosis in women who were fed soy-based formulas as infants (3). 

However, two other studies have found no evidence that the consumption of soy was associated with endometriosis and may even be associated with a reduced risk (5, 6). 

I HAVE ENDOMETRIOSIS, SHOULD I AVOID SOY?

Given the results from the studies are mixed there isn’t a definitive yes or no. However, if you are concerned about soy consumption and endometriosis, then stick to a wholefoods diet with plenty of vegetables, fruit and omega 3 fats and avoid processed foods, including processed soy foods. If you do consume soy, stick to traditionally fermented soy products such as miso and tempeh.

If you’re feeling unsure about whether soy is a problem for you and might be triggering symptoms, talk to a qualified nutritionist.

References

(1) Parazzini, F., Viganò, P., Candiani, M., & Fedele, L. (2013). Diet and endometriosis risk: A literature review. Reproductive BioMedicine Online, 26(4), 323–336. doi:10.1016/j.rbmo.2012.12.011

(2) Marquardt, R. M., Kim, T. H., Shin, J. H., & Jeong, J. W. (2019). Progesterone and Estrogen Signaling in the Endometrium: What Goes Wrong in Endometriosis?. International journal of molecular sciences, 20(15), 3822. doi:10.3390/ijms20153822

(3) Upson, K., Sathyanarayana, S., Scholes, D., & Holt, V. L. (2015). Early-life factors and endometriosis risk. Fertility and sterility, 104(4), 964–971.e5. doi:10.1016/j.fertnstert.2015.06.040

(4) Mvondo, M. A., Ekenfack, J. D., Minko Essono, S., Saah Namekong, H., Awounfack, C. F., Laschke, M. W., & Njamen, D. (2019). Soy Intake Since the Prepubertal Age May Contribute to the Pathogenesis of Endometriosis in Adulthood. Journal of Medicinal Food. doi:10.1089/jmf.2018.0160

 (5) Tsuchiya, M., Miura, T., Hanaoka, T., Iwasaki, M., Sasaki, H., Tanaka, T., … Tsugane, S. (2007). Effect of Soy Isoflavones on Endometriosis. Epidemiology, 18(3), 402–408. doi:10.1097/01.ede.0000257571.01358.f9

(6) Mumford, S. L., Weck, J., Kannan, K., & Buck Louis, G. M. (2017). Urinary Phytoestrogen Concentrations Are Not Associated with Incident Endometriosis in Premenopausal Women. The Journal of nutrition, 147(2), 227–234. doi:10.3945/jn.116.238840