Isoflavones and menopause: everything you need to know!

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Soy isoflavones

Phytoestrogens are plant compounds that are metabolized to substances with estrogenic activity. They have a chemical structure similar to that of estradiol, which is the strongest estrogen. The main sex hormone in women is estradiol (E2) while two other less concentrated hormones are estrone (E1) and estriol (E3). Estrogenic action is induced when a hormone or phytoestrogen binds to estrogen receptors (there are at least two receptors, ERA and ERβ).

Phytoestrogens or herbal estrogens have been suggested as an alternative to treating hormonal replacement during menopause. In the 1990s, in the United States, a large percentage of women underwent hormone replacement therapy that included the administration of estrogen with or without progesterone. In 2002, after nearly half a century of treatment, the Women’s Health Initiative study was discontinued prematurely because women taking estrogen and progesterone had several side effects. Following this data, there has been a shift to alternative therapies for the effects of menopause and the use of phytoestrogens.

More than 300 plants consumed as part of a normal diet contain phytoestrogens. These are mainly flavonoids – substances that belong to the phenolic compounds. Their two most important categories are cumestan and isoflavones. Chestnuts are the strongest phytoestrogens but are found mainly in clover and alfalfa plants, so they are rarely part of the human diet. Isoflavones are of great interest because in addition to being found in red clover, they are abundant in soy and flaxseed, while they are also found in legumes such as chickpeas, lentils and beans. Another important class of phytoestrogens, which does not belong to flavonoids, is lignans, which are found in many fruits and whole grains.


There are more than 1,000 types of isoflavones, but genistein, daidzein, and glycitein have been studied. Pure soy protein is the most concentrated source of isoflavones (about 100 mg per 100 g of soy protein). Secondary soy products (milk and flour) contain smaller amounts e.g. a cup of soy milk provides 30 mg and a cup of soy yogurt 21 mg.

Isoflavones are inert plant forms that are metabolized by bacteria in the intestinal flora during digestion. Only after this transformation is completed can they be absorbed and exert their effects. When foods rich in isoflavones are consumed, they circulate in the blood for several days and sometimes in multiple amounts compared to endogenous estrogens. However, their mode of action is complex because they have a mixed estrogenic effect,  they sometimes mimic estradiol and sometimes compete with it. A laboratory study showed that they act competitively before menopause due to high levels of estrogen circulating in the female body, but act as estrogen after menopause due to low levels of endogenous estrogen [1].

Estrogens regulate female fertility but are essential in other important processes such as skeletal maintenance, electrolyte balance, skin physiology, cardiovascular system and central nervous system, and also play an important role in carbohydrate and metabolism. fats. There are indications that a diet rich in isoflavones may help prevent various conditions such as cardiovascular disease, osteoporosis and menopausal symptoms. However, despite ongoing research, the role of health equivalents remains controversial as clinical trials, although many, are usually small. In particular, in the case of women diagnosed with hormone-sensitive cancer, it is preferable to avoid isoflavones.

  At the onset of menopause, estrogen decreases significantly and this can cause vasomotor symptoms associated with regulating body heat. Outbreaks appear to be exacerbated during the first five to five minutes. They initially manifest as intense heat release on the face and chest area and can spread throughout the body.

Soybean intake is estimated to be 4-9 times higher in Asian countries such as Japan, Korea, China, Taiwan and Indonesia, compared to Western countries such as the United States and women in Asian countries report a lower frequency of hot flashes. only 10–25% compared with 60–90% of women in Western countries [2].

  According to a research, taking a herbal supplement containing 72 mg of isoflavones from soybeans and red clover for 6 months significantly reduced hot flashes during menopause. Another study, in 51 healthy postmenopausal women, found a 57% reduction in the frequency and severity of hot flashes after daily supplementation for 12 weeks containing 60 mg of isoflavones [4].

Isoflavones and οsteoporosis

After menopause, women are at high risk of losing bone mass due to a decrease in estrogen. A balanced diet that includes protein, calcium, magnesium, and vitamins K, C, E, and B plays a key role in preventing osteoporosis. Because there are high levels of ERv receptors in the bones, isoflavones could theoretically slow bone loss.

Indeed, a meta-analysis showed less spinal bone loss after 6 months of taking a 90 mg isoflavone supplement daily [5]. In 2015, a study of 200 volunteers who underwent the first two years of menopause found that after six months, women who took soybeans had lower levels of a protein called ßCTX in their blood, the presence of which indicates a loss of bone mass.

Isoflavones and heart health

It is known that the incidence of cardiovascular events in women increases after menopause and, in theory, isoflavones may reduce the risk by acting as estrogen substitutes. In 1999, the US Food and Drug Administration (FDA) allowed food manufacturers to claim that high levels of soy protein could help reduce the risk of heart disease. However, this does not mean that the risk reduction is due to isoflavones – it can be attributed to other ingredients in soy.

There are not enough studies on the role of isoflavones in heart health. A recent study published in 2020 included 74,241 from Nurses ‘Health Study I (1984–2012), 94,233 women from Nurses’ Health Study II (1991–2013), and 42,226 men from Health Professionals Follow-Up Study ( 1986–2012) found that higher intake of isoflavones and tofu (produced from soy milk such as cheese) was associated with a moderately lower risk of heart disease. Favorable association with tofu was more pronounced in both young and postmenopausal women who did not use hormones.

Isoflavones and breast health

In recent decades, isoflavones have attracted the attention of researchers due to the “Japanese phenomenon“,  the lower incidence of certain chronic diseases in the Japanese, including certain cancers. It has been suggested that the cause may be higher soy consumption from an early age. In some Asian countries, adults can consume 15-50 mg of isoflavones a day from soy products, compared to just 2 mg in some Western countries.

Although there is an epidemiological link between soy and lower risk of breast cancer, the issue is complex as not all isoflavones always have the same effect [7, 8, 9]. When it comes to women who have been diagnosed with hormone-sensitive breast cancer, soy can actually prove harmful because of its estrogenic action. Experts advise women with breast cancer not to include soy in their diet, as it is not fully understood how it affects the risk of breast cancer, its development and recurrence.

Side effects

  Although there are many health benefits to soy consumption, there are side effects. It should be noted that despite two decades of intensive research, the biological pathways of isoflavones and their metabolites have not been fully understood. Precisely for this reason, taking isoflavone supplements during pregnancy and lactation should be avoided.

One possible side effect is that in some people soy can affect thyroid function, especially in people whose glands are malfunctioning. Zinc and iodine are essential nutrients for the production of T3 and T4 hormones, but soy can block the uptake of iodine by the thyroid and the function of zinc. Therefore, if there is a malfunction of the thyroid gland, it is advisable to avoid excessive consumption of soy and its products.

High intake of isoflavones is associated with reduced fertility in animal studies. In the 1940s, it was first realized that certain plant compounds could act as estrogen or inhibit their activity when it was observed that sheep grazing in meadows with red clover had fertility problems. The estrogenic effects of isoflavones can also affect male fertility. It is found that eating soy foods was associated with a reduced sperm count in men. Other studies have not found this effect, but there are indications that isoflavones may affect sperm quality.

Finally, soy is one of the foods that can cause allergic reactions.

At you will find a wide variety of isoflavone supplements!


  1. Phytoestrogens: a viable option?
  2. Self-reported menopausal symptoms in a racially diverse population and soy food consumption.
  3. Efficacy on menopausal neurovegetative symptoms and some plasma lipids blood levels of an herbal product containing isoflavones and other plant extracts.
  4. Isoflavone treatment for acute menopausal symptoms.
  5. Soy isoflavone intake increases bone mineral density in the spine of menopausal women: meta-analysis of randomized controlled trials.
  6. Isoflavone Intake and the Risk of Coronary Heart Disease in US Men and Women.
  7. Soy, Red Clover, and Isoflavones and Breast Cancer: A Systematic Review.
  8. Dietary isoflavones or isoflavone-rich food intake and breast cancer risk: A meta-analysis of prospective cohort studies.
  9. Dietary isoflavone intake and all‐cause mortality in breast cancer survivors: The Breast Cancer Family Registry.
  10. Soy food and isoflavone intake in relation to semen quality parameters among men from an infertility clinic.
  11. Associations between semen phytoestrogens concentrations and semen quality in Chinese men.

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