In my practice, phytoestrogens are one of the most commonly misunderstood foods and supplements for women. Particularly women who have breast cancer.

What is estrogen?

In the female body, estrogen is the primary sex hormone. It works as part of a complex cascade to control development and regulation of the reproductive tract, as well as things like breast development, libido and fatty tissue deposits known as secondary sex characteristics. To understand phytoestrogens, it’s also important to understand that a woman’s body produces three types of estrogen. These are: estrone, estriol, and estradiol (estradiol is the strongest). To create changes in the body, estrogen binds to receptor sites on tissues. In some women with cancer, estrogen binding to a receptor site can stimulate its growth. These are called estrogen-positive cancers.

What are phytoestrogens?

Unlike our own estrogen produced by the ovaries, phytoestrogens come from plants. While phytoestrogens may look like estrogen, they are much weaker than our own estrogen, especially estradiol. You will come across phytoestrogens in foods like soy and flax.

Why are people fearful of phytoestrogens?

For some time, there was an accepted understanding in the medical community that phytoestrogens were similar enough to endogenous estrogens that they could cause health issues for women in relation to hormone balancing, in particular for women with an estrogen receptor-positive cancer diagnosis. Many theorized that, for women who have a hormone-positive breast cancer, even things that resemble estrogen may bind to receptor sites and cause stimulation of cancer growth. As a result, until very recently phytoestrogens were often eliminated from nutrition and supplement recommendations for women with, or a history of, estrogen positive cancers.

Should You Worry About Consuming Phytoestrogens?

More recently, research of phytoestrogens, hormones and cancer are showing us some really interesting things! Phytoestrogens don’t seem to bind and activate receptor sites – that is, they don’t have strong actions like estradiol. Instead, it appears they rest in the receptor sites, blocking estrogens from being able to bind, which reduces growth stimulation in cancer. Thirty-three randomized controlled trials have concluded that soy does not appear to have estrogenic effects in hormone-sensitive tissues (e.g., breast, uterine), and may be protective against development of cancer in these locations. The American Cancer Society has supported women with breast cancer consuming 2-3 servings per day of soy, preferably with less-processed sources (such as tempeh, tofu and edamame). In studies on flax, researchers also concluded no evidence of estrogenic activity in hormone-sensitive tissues. Consuming 2-4 tablespoons daily is a rich source of fibre and may also be protective.

To Sum Up:

Phytoestrogens and estrogens are not the same, and their behaviour in the human body also appears to be different. New research suggests daily consumption of phytoestrogens – specifically soy and flax – is safe, even for women with breast cancer.

Please note: it’s important to check with your oncology team and/or naturopathic doctor ahead of making any changes to your diet or supplements, especially if you are taking any medications. This article should be used to supplement, not replace, individualized medical advice from your medical team.

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