Although low estrogen levels can cause a variety of symptoms in women, higher estrogen levels can also cause health problems. In addition, higher estrogen levels are linked to a higher risk of breast cancer in women. High estrogen can also cause issues for men.
Many people want to make sure that they control their estrogen levels. Many people have heard that soy affects estrogen. However, the story can be conflicting, with some sources claiming that soy increases estrogen while others claim the opposite.
What does the evidence say? Does soy milk affect hormones? Does soy boost estrogen, or tamp it down?
The reason why many people are concerned about a link between soy and estrogen levels has to do with a class of compounds called isoflavones, also known as phytoestrogens. Found in all types of soy products, from tofu to soy milk, phytoestrogens are able to bind to the estrogen receptors on your cells, but much more weakly.
Some people are concerned that a phytoestrogen would act like estrogen. However, the phytoestrogen doesn’t stimulate the estrogen receptor as much as estrogen itself does, but it does block estrogen from reaching the receptor. Because of this, phytoestrogens may actually decrease estrogen’s effects in the body, by blocking estrogen from binding to cells. In fact, this is similar to the mechanism of action of tamoxifen, a common estrogen blocking treatment that’s used in women who have undergone treatment for estrogen receptor-positive breast cancer.
The story on soy and women’s hormones is complex, and this topic is still being debated in the scientific literature. It’s difficult to make blanket studies on soy, for a few different reasons. People’s consumption of soy may not be consistent over the course of their lifetime, and they may not always report it accurately. There are also many different types of soy products, with different levels of phytoestrogens. The effects of soy may differ depending on a person’s estrogen levels – it’s possible that soy could have an estrogenic effect if your levels are low, but block estrogen if your levels are high.
The evidence that we do have seems to suggest that soy may be neutral or slightly protective against breast cancer. It might also have a small effect on relieving menopausal symptoms (like hot flashes), but is much weaker than hormone replacement therapy, with some studies showing no effect at all. Overall, the evidence seems to suggest that there’s no particular reason to worry about soy consumption, but experts have not made a blanket recommendation for everyone to eat more of it either.
Tofu is made from condensed soy milk. Like most types of soy milk, it’s unfermented. If estrogen is affected by normal soy milk (such as Silk Milk), estrogen is likely to also be affected by tofu. There are also fermented forms of soy, such as tempeh, miso, soy sauce, and fermented soy milk. Fermentation has been found to increase the bioavailability of the phytoestrogens in soy, making them easier for your body to absorb. Because of this, eating fermented soy products may have more of an effect than unfermented ones do.
Estrogen levels that are too high or too low can create a variety of health problems, and high estrogen is linked to breast cancer risk. If you’re concerned about your estrogen levels, then you may want to consider getting your levels tested. This is the only way to know whether you have high estrogen levels. Many people choose to get a complete hormone panel, rather than testing the level of just one hormone, because this allows you to understand the state of your overall hormonal health, including the ratios of different hormones to each other.
You can ask your doctor to order hormone tests for you, although this requires an office visit. If you’d rather avoid the hassle of going to the doctor just to ask for the test, you can order it yourself online, and either go to a lab for your blood draw or take your blood sample yourself at home using a fingerprick. You will then receive your results online within a few days. If your results are abnormal, you will often be offered a consult with a medical professional by telehealth to discuss next steps.
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Estrogen. National Institutes of Health. https://www.ncbi.nlm.nih.gov/books/NBK538260/. Accessed 26 July 2022.
Estrogen-Dependent Cancers. Cleveland Clinic. https://my.clevelandclinic.org/health/diseases/10312-estrogen-dependent-cancers. Accessed 26 July 2022.
Hutchins AM, Slavin J, et al. Urinary isoflavonoid phytoestrogen and lignan excretion after consumption of fermented and unfermented soy products. J Am Diet Assoc. 1995 May;95(5):545-51. doi: 10.1016/S0002-8223(95)00149-2.
Straight Talk About Soy. Harvard School of Public Health. https://www.hsph.harvard.edu/nutritionsource/soy/. Accessed 26 July 2022.
Trock BJ, Hilakivi-Clarke L, et al. Meta-analysis of soy intake and breast cancer risk. J Natl Cancer Inst. 2006 Apr 5;98(7):459-71. doi: 10.1093/jnci/djj102.