Are Soy Formula and Fibroids Connected?

You may have heard that soy should be eaten in moderation due to its ability to mimic estrogen in the body. Soy has been eaten in Asian cultures for a very long time in the form of tofu, miso, tempeh and soy milk. It is true that soy contains phytoestrogens, but they act as a very weak form of estrogen. There is overwhelming evidence that eating soy is safe – there are even studies that show that up to two servings a day of soy can reduce the risk of breast cancer.

The Link Between Estrogen and Fibroids

Fibroids are an extremely common gynecological condition – up to 80% of women will have a fibroid within their reproductive life cycle. However, not all fibroids are problematic and cause women to suffer with pain and heavy bleeding. For those women who are negatively impacted by fibroids, symptoms like intense menstrual pain, heavy menstrual bleeding, bleeding between periods, lower back pain, frequent urination and abdominal bloating are common. Fibroids are the number one cause of uterine hysterectomy in the United States.

Our knowledge of fibroids and what causes them has come along way since the days when our mothers and grandmothers suffered from pain and bleeding that couldn’t be well explained. Research and observation has led us to understand that hormones affect fibroid growth. Fibroids tend to get larger during pregnancy (when estrogen is high) and shrink after menopause (when estrogen is reduced).

Fibroids, Estrogen and Soy

Your body produces estrogen, a hormone that gives you your womanly curves, helps your body enjoy sex, regulates your period and also causes fibroids to grow. Because the fibroids in your uterus are under the same influence of other hormones in your body that make you have your period, the fibroids bleed in addition to the lining of your uterus, causing excess blood during your menstrual cycle.

Some women who follow a fibroid reduction diet choose to avoid foods with soy to limit the amount of extra estrogen they consume. A new study published in November 2015 in Environmental Health Perspectives took a look at soy and how it affects the growth of fibroids in African American women, a group who are at high risk for fibroids. This study focused on adult African American women who had been fed soy formula as infants.

The study did not find an association between soy and the prevalence of fibroids. This means that women who were fed soy formula were not more likely to develop fibroids as adults than women who did not receive soy formula as infants. However, the study did find that in women who did develop fibroids as adults, women who had been fed soy formula as infants had much larger fibroids than those who were not fed soy formula. The increase in the size of fibroids was remarkable – women who had received soy formula had fibroids that were 32% larger in diameter and 127% larger in volume.

So does this mean that soy formula and fibroids are connected? This particular study tells us that while soy doesn’t cause fibroids, it could increase fibroids in women who are already predisposed.


O’Connor, A. Ask Well: Is It Safe to Eat Soy? – The New York Times. (September 27, 2013.). Retrieved from

Upson, K., Harmon, Q. E., & Baird, D. D. (2015). Soy-Based Infant Formula Feeding and Ultrasound-Detected Uterine Fibroids among Young African-American Women with No Prior Clinical Diagnosis of Fibroids. Environmental Health Perspectives.

Content Sponsored by: MIRI Women – The Minimally Invasive Reproductive Surgery Institute (MIRI) brings together highly skilled, board-certified specialists who are focused on women’s health. Our team of professionals is trained in advanced gynecology, specifically hysterectomy surgery. Philosophically, our partner physicians take a “less is more” approach to health care, by first treating patients with the most conservative therapies. MIRI focuses on physical healing, while emphasizing that a patient’s emotional well-being is just as important.

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