The Great Debate: Phytoestrogens

The Great Debate: Phytoestrogens

We love a good debate, but some discussions can leave us feeling more confused than when we began. A prime example is the debate over phytoestrogens. Are they good for us or bad? Read on as we untangle the health claims and explain why unprocessed soy and flax products should be part of a well-balanced diet for most women.

What’s up with phytoestrogens?

Phytoestrogen-rich foods have received a whole load of attention over the last 60 years. This is in part due to a global increase in plant-based eating, but also due to the phytoestrogens properties. These phytoestrogens are naturally-occurring plant-derived compounds that, because they look chemically similar, can function as a mild form of estrogen within the body. There’s been decades of raging debate over whether, because of this, consuming phytoestrogens found in products such as soy can help or harm us. But (and here comes the spoiler alert) increasing evidence now suggests that consuming these products may provide relief from a range of conditions, including menopause.

Menopause and soy

Menopause can have several uncomfortable side-effects: for example, 75-85% of women experience hot flashes that can lead to insomnia and diminished sleep quality (National Sleep Foundation 2019). However, nutrition and lifestyle can have a vital role in managing these symptoms. For example, one meta-analysis of studies examining the use and effectiveness of plant-based therapies on menopausal symptom relief found phytoestrogen-containing foods and dietary supplements may reduce hot flashes and vaginal dryness. Whilst the products had no significant effects on night sweats, this does seem promising for the use of soy in the management of several key menopausal symptoms (Franco et al. 2016).

Cancer and phytoestrogens

Because phytoestrogens have estrogen-like properties, it was once commonly believed that consuming products which contained high amounts of phytoestrogens, such as soy and flax seeds, could increase an individual’s risk of developing chronic diseases, including breast cancer. However, there is no conclusive evidence that this is true. In fact, soy products in particular have been investigated for their role in helping reduce the risk of some cancers, including breast and prostate cancer (Messina 2003, Trock et al. 2006). During the reproductive years, the active form of estrogen is estradiol. It is oxidized mainly in the liver to estrone. Estrone can be converted to two metabolites: 2-hydroxyestrone (2OHE1) and 16α-hydroxyestrone (16OHE1). 16OH1 has been shown to increase the estrogen’s activity and promote the growth of cancer cells. Two separate clinical trials have shown that a diet including 10 or 25 g of ground flaxseed for 7 or 16 weeks leads to increased 2OHE1 in the urine, without an increase in the excretion of 16OHE1 (Haggans et al. 1999). This is encouraging evidence for the role of both soy and flax in estrogen related cancers.

Hypothyroidism and phytoestrogens

Despite this, there is still concern about the relationship between phytoestrogens and thyroid health, especially among individuals whose thyroid function is already compromised. The ongoing debate among the research community about soy products, a key source of phytoestrogens, and hypothyroidism has been especially long and controversial.

This is because genistein and daidzein, the main phytoestrogens in soybeans, are also goitrogens that can interfere with the thyroid’s ability to produce key hormones. However, we’ve known for some time that their effects can be potentially reversed by iodine supplementation (Van Wyk et al. 1959, Shephard et al. 1960).

Again, this is great news for menopausal and perimenopausal women wanting to use soy products to manage their symptoms. For example, researchers found menopausal women taking phytoestrogen dietary supplements who had adequate iodine intake weren’t at risk of developing any thyroid gland disorders (Sosvorová et al. 2013).

In fact, a review of human studies found no significant issues with taking phytoestrogens. However, the authors also acknowledged that more research needs to be conducted (Messina & Redmond 2006). If in doubt with regards to your hormone health and micronutrient balance, we recommend lab testing like the Dutch comprehensive hormone test and NutrEval micronutrient panel. Testing provides insight into your own hormone and nutrients levels; through this information we can modulate specific nutrients and ways of eating.

The verdict?

When managed correctly, phytoestrogen-rich foods can be part of a balanced diet for most people and, in their unprocessed form, are likely to provide health benefits. Unprocessed soy products; such as edamame beans, tempeh, tofu and miso; contain high-quality protein (they actually contain all 8 essential amino acids), are rich in B vitamins, fiber, potassium, and magnesium. Fresh flaxseeds are an excellent source of omega 3 fatty acids, magnesium, phosphorus, manganese, vitamin B1, selenium, and zinc. Ensure you also consume adequate food sources of iodine such as seafood and sea vegetables.

As with all things nutrition, make sure that when making any dietary changes (especially if you are currently on medication or experiencing any medical issues), you consult the advice of your health professional. If you’re ready to start learning how to individualize your diet, you can learn more about working with Lauren 1:1 here.

In Health,
Lizzy Cangro


Franco, O.H., Chowdhury, R., Troup, J., Voortman, T., Kunutsor, S., Kavousi, M., Oliver-Williams, C. and Muka, T., 2016. Use of plant-based therapies and menopausal symptoms: a systematic review and meta-analysis. Jama, 315(23), pp.2554-2563.

Messina, M.J., 2003. Emerging evidence on the role of soy in reducing prostate cancer risk. Nutrition reviews, 61(4), pp.117-131.

Messina, M. and Redmond, G., 2006. Effects of soy protein and soybean isoflavones on thyroid function in healthy adults and hypothyroid patients: a review of the relevant literature. Thyroid, 16(3), pp.249-258.

National sleep foundation (2019) Menopause and sleep [Online]. Available from: https://www.sleepfoundation.org/articles/menopause-and-sleep

Shepard, T.H., Pyne, G.E., Kirschvink, J.F. and McLean, M., 1960. Soybean goiter: report of three cases. New England Journal of Medicine, 262(22), pp.1099-1103.

Sosvorová, L., Mikšátková, P., Bičíková, M., Kaňová, N. and Lapčík, O., 2012. The presence of monoiodinated derivates of daidzein and genistein in human urine and its effect on thyroid gland function. Food and chemical toxicology, 50(8), pp.2774-2779.

Trock, B.J., Hilakivi-Clarke, L. and Clarke, R., 2006. Meta-analysis of soy intake and breast cancer risk. Journal of the National Cancer Institute, 98(7), pp.459-471.

Van Wyk, J.J., Arnold, M.B., Wynn, J. and Pepper, F., 1959. The effects of a soybean product on thyroid function in humans. Pediatrics, 24(5), pp.752-760.

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