THERE IS NO DEFINITIVE EVIDENCE THAT SOY CONSUMPTION causes breast cancer. As an oncologist, I have a special interest in breast cancer. “Can I eat soy?” is a common question I get. Today I want to address the cancer myth my patients with breast cancer seem to always ask about: Does soy increase breast cancer risk?
“The idea that there could be one solution to breast cancer- screening, early detection, some universal cure- is certainly appealing. All of us, those who fear the disease, those who live with it, our friends and families, the corporations who swath themselves in pink, wish it were true. Wearing a bracelet, sporting a ribbon, running a race, or buying a pink blender expresses our hopes and that feels good — even virtuous. But making a difference is more complicated than that.”
― Peggy Orenstein, Don’t Call Me Princess: Essays on Girls, Women, Sex, and Life
What is estrogen?
Estrogen is one of two sex hormones often associated with people assigned females at birth. Along with progesterone, estrogen plays a central role in reproductive health. The development of secondary sex characteristics (including the hips, breasts, etc.), menstruation, pregnancy, and menopause are all possible partially because of estrogen.
Estrogen plays an essential role in other body systems, too. For this reason, although people assigned females at birth have the most estrogen, all genders make this hormone.
Estrogen plays an important role in other body systems, too. For this reason, although people assigned females at birth have the most estrogen, all genders make this hormone.
There are three major estrogen forms:
- Estrone (E1) is the primary estrogen form that the body makes after menopause.
- Estradiol (E2) is the primary estrogen type in the body during reproductive years. It is the most powerful estrogen form.
- Estriol (E3) is the main estrogen type during pregnancy.
What Are Phytoestrogens?
Phytoestrogens are a natural compound found in plants and plant-based foods. These substances have a chemical structure similar to 17-beta estradiol.
Phytoestrogens consist primarily of isoflavones (high concentrations in soybeans and other legumes) and lignans (in various fruits, vegetables, and cereal products).
When you eat plant-based foods with phytoestrogens, the substances can produce effects similar to natural estrogen. Given this similarity, phytoestrogens are known as dietary estrogens. While there are phytoestrogen supplements, I counsel my patients to get these from the diet.
Phytoestrogens (Including Soy) and Breast Cancer
Does consuming phytoestrogens such as soy increase the odds of getting breast cancer? A 2014 meta-analysis of eight studies examining the impact of soy intake on breast cancer risk discovered the following:
Analysis of the pooled results of studies in Asian countries suggests that soy isoflavone is protective in pre- and postmenopausal women. The risk reduction is by a relative 40 percent.
Does this apply to women in Western countries? Pooled studies show that soy isoflavone has only a borderline protective effect, dropping absolute risk by approximately one percent.
The meta-analysis showed a lower breast cancer risk for those consuming high levels (more than 15 milligrams daily) of soy and isoflavones compared with those consuming less.
From the total number of breast cancer cases, 75 percent (7,271 patients) belonged to the 0–15 mg/day group, while only 25 percent (2,428 patients) belonged to the group consuming >15 mg/day. There is an association between high soy consumption and breast cancer risk reduction.
Key Points — Soy and Breast Cancer Risk
Question. Does phytoestrogen (such as soy) consumption increase breast cancer risk?
Findings. The meta-analysis discovered an association between high levels of soy consumption and a lower breast cancer risk.
Meaning. There is no high-level evidence that phytoestrogen consumption increases breast cancer risk. The current meta-analysis suggests the opposite: Soy consumption over 15 milligrams daily is associated with a lower breast cancer risk, at least in Asian countries. While causality cannot be established, it is reassuring that consuming phytoestrogens does not appear to increase breast cancer risk.
Conflicts. The study authors report no conflicts of interest.
Finally, soy foods are chock full of beneficial nutrients associated with a lower heart disease risk. I use it to pack my diet with high-quality protein, vitamins, fiber, and minerals.
Enjoy your tempeh, tofu, edamame, soy milk, and miso. Just not all at once!
If you know someone with breast cancer, here is my comprehensive online course:
Breast Cancer – What a Patient Needs to Know.
Breast cancer information can be incredibly valuable for navigating breast cancer management. breastcancerbydrhunter.thinkific.com.
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The information I provided in this blog is for educational purposes only and does not substitute for professional medical advice. Please consult a medical professional or healthcare provider for medical advice, diagnoses, or treatment. I am not liable for risks or issues associated with using or acting upon the information in this blog.
Thank you for reading “The Cancer Myth My Patients Always Ask About.”
