Phytoestrogens: to eat soy or to not eat soy?


Yes, this meal is safe to eat. Photo courtesy of United Soybean Board.

Are phytoestrogens like soy safe to eat?

This is a common question in my office. People tell me they have heard soy has strong estrogen-like effects that will worsen PMS or PCOS. They have heard that soy is bad for the thyroid. Soy might even disrupt men’s hormones and cause them to grow breasts. These stories are circulated in the media, particularly online and social media, often enough that I appreciate why people ask the question: are phytoestrogens like soy safe?

The TLDR answer is: yes, soy and other phytoestrogens are safe for women and men to eat.  In many cases, they may even be protective for women experiencing problems related to high or low estrogen levels.

What are phytoestrogens?

Phytoestrogens are plant compounds that have estrogen-like properties. This is because their shapes loosely resemble the shape of a naturally occurring estrogen molecule, estradiol. But whereas estradiol fits in an estrogen receptor perfectly, like a key in a lock, phytoestrogens do not. Phytoestrogens are more like a toy key that you give a toddler to play with. Phytoestrogens gently nudge estrogen receptors, simultaneously creating a small amount of estrogenic activity and blocking the receptor from receiving stronger stimulation from other sources.

And this is where the therapeutic effect of phytoestrogens comes from: in situations where estrogen levels are already too high, phytoestrogens protect estrogen receptors from overstimulation. And in situations where estrogen levels are uncomfortably low, like menopause, the gentle nudge against an estrogen receptor may provide just enough activity to relieve discomfort.

In other words, phytoestrogens modulate estrogen levels. When natural estrogen levels are high phytoestrogens have a net anti-estrogen effect, and when natural estrogen levels are low their effect becomes more estrogenic.

Where do phytoestrogens come from?

There are 2 main types of phytoestrogen: isoflavones and lignans.

  • Isoflavones: a plant molecule found in the plant family Fabacea (bean family), especially soybeans.
    • Highest concentrations in: edamame or whole soy beans, tempeh, tofu, miso, soy butter
    • Other sources: chickpeas, peanuts
  • Lignans: a component of insoluble fiber, found in many plants.
    • High concentrations in: flax seeds, sesame seeds, cereal brans (e.g. oat bran, rice bran)
    • Other sources: whole grains (wheat, millet, rye, barley), legumes, nuts, asparagus, grapes, kiwi, lemons, oranges & pineapple

Dietary lignans depend on healthy gut flora to metabolize or change them into a form where they are biologically active. And it is not just the estrogen receptor activity that makes lignans healthy, they also have beneficial effects on the cardiovascular system.

Phytoestrogens and Digestive Health:

If phytoestrogens were a cure-all for estrogen related problems, it wouldn’t be a secret. But they do have a measurable and meaningful impact on many hormonal imbalances. For example:

A 2015 meta-analysis of 15 studies done on phytoestrogens and menopausal symptoms shows that they are able to reduce frequency of hot flashes compared to placebo.

A 2012 quasi-randomized study of 146 women with PCOS in Italy showed that use of a phytoestrogen lignan isolate for 3 months reduced levels of DHEA-S and testosterone and improved lipid profiles by reducing triglycerides and LDL (aka “bad cholesterol”) levels.

Clinically, I suspect that one of the keys to how people respond to phytoestrogens is contingent on the state of their digestive health. It is known that lignans, for example, need to undergo transformation by healthy gut bacteria to become fully active as phytoestrogens in the body. And the balance between healthy and unhealthy gut bacteria is also likely the lynch pin for whether people find foods containing phytoestrogens beneficial for their hormonal and metabolic balance, or a cause of gas, bloating and fatigue.

Not everyone responds well to soy and other foods rich in phytoestrogens. Digestive problems are common among people who do not tolerate soy and other legumes well.  One reason for this is the fructo-oligo-saccharide content of legumes, recall that the legume family is the plant family most well known for producing phytoestrogens, are fodder for the fermenting bacteria responsible that cause the digestive condition SIBO (small intestine bowel overgrowth).

This underscores why digestive health is such a critical piece of the puzzle in finding hormonal balance for many women. Fortunately, there are tests available to evaluate digestive health, including tests for SIBO to see if there is a bacterial overgrowth that requires treatment before phytoestrogens can be successfully tolerated and metabolized, as well as tests to determine the presence, abundance and diversity of healthy gut bacteria.

About the author:

Miranda Marti, ND, LAc is a body positive naturopathic physician and acupuncturist specializing in the holistic treatment of PCOS and other chronic conditions affecting hormonal, digestive and mental health.

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