There is a clear need for further carefully designed studies to elucidate the effects of phytoestrogen consumption on the endocrine system. In general, the available evidence for an association between dietary phytoestrogens and endocrine biomarkers is inconclusive. Regarding bone remodeling, the effects of phytoestrogens on OC concentrations are unclear, and their beneficial impact may arise instead from reducing bone resorption by osteoclasts. Among stress response-related hormones, no significant changes in cortisol are described in healthy women or in those at cardiometabolic risk, but a lower production of cortisol is reported in equol-excretors. In premenopausal women, usually studied separately from postmenopausal women, uncertain results have been obtained regarding sex hormones, breast cancer protection, and bone remodeling. Although phytoestrogens transfer from maternal blood to the fetus, no effects have been observed in early life. A possible explanation for these contrasting results could be that estrogens are predominantly antiresorptive agents, so the beneficial effects of phytoestrogens may arise from decreased bone resorption by osteoclasts rather than increased bone formation by osteoblasts.
As well as a decline in estrogens, a significant decrease in progesterone levels after phytoestrogen consumption has been observed 47,48,49,52. Several studies have focused on the beneficial effect of soy isoflavones, specifically genistein and daidzein, as these components can act as weak estrogens. However, in an open-labeled, non-randomized clinical trial of men with higher levels of PSA, free testosterone was depleted after 12 months of daily consumption of 141 mg of isoflavones in soy milk . A cross-sectional study in randomly selected Japanese men found a negative association between soy product consumption and E2 serum concentrations, but no link was observed with peripheral concentrations of androgen hormones . In a crossover trial conducted in girls aged 8–14 years, the consumption of a high-soy diet for 8 weeks significantly increased dehydroepiandrosterone (DHEA) concentrations but not other sexual hormones. Nevertheless, a cross-sectional study carried out in children aged 3–6 years reported an increase of androgens in girls and a decrease of estrogens in boys consuming higher amounts of soy and isoflavones . The results of a longitudinal study that measured E2, estriol (E3), testosterone, and isoflavones in urine and serum from 194 pregnant women weakly support the initial hypothesis that genistein and daidzein would reduce levels of E2 and testosterone at the 10th week of gestation.
The effect of soy on thyroid function needs further examination. However, the actual number of men eating very high amounts of tofu was small, and past dietary information was collected by relying on the participants’ memory, some of whom may have already experienced cognitive decline. One large study in men found a detrimental effect on cognitive function. The soy isoflavone, daidzein, has been hypothesized to reduce decline in cognitive function or disease processes related to cognition and behavior. They also find that soy can reduce inflammation and excess free radical production in the brain. In some tissues and in some people, they may block the action of estrogen.
Some scientists are concerned that a high intake of phytoestrogens may disrupt the body’s hormonal balance. Even moderate drinking can impact your hormones more than phytoestrogens. About 30–50% of people have gut bacteria that convert certain phytoestrogens into compounds that have stronger effects. While most men have nothing to worry about, there are a few situations where phytoestrogens might be a problem for your hormones. It has been hypothesized that phytoestrogens may interfere with the IGF system through their effects on steroid hormone physiology or by disrupting GH and IGF signaling . However, previous studies report unaltered OC levels 170,171, indicating a need for more research on the phytoestrogen effects on bone metabolism in premenopausal women.
In agreement with the potential anti-estrogenic effect of phytoestrogens, some authors have observed a significant decrease in estrogen levels after the consumption of soy products 18,22,47,48,49. The intake of phytoestrogens has increased due to the widespread use of soy products for human consumption and as cattle food . For those with low estrogen, adding more sources of phytoestrogens to the diet may reduce symptoms or the risk of osteoporosis. More research is necessary to understand the potential benefits and risks of consuming high levels of phytoestrogens. People may see adverse effects when consuming phytoestrogens at very high levels. Research indicates that most people in Western countries do not eat enough phytoestrogens for them to have any health effects.
In addition, observational studies have found an increased risk of prostate cancer in Chinese and Japanese men who move to Western countries and adopt a Western diet, but not in those who continue eating a traditional diet. The incidence of prostate cancer is highest in Western countries and lowest in Asian countries, where soy foods are a regular part of the daily diet. Another prospective study followed 1,954 American women who were breast cancer survivors for six years. Eating soy foods starting at an early age (such as those found in many traditional Far East Asian diets) may be why women from some countries find greater benefit from soy foods than others. In animal and cell studies, high dosages of isoflavone or isolated soy protein extracts tend to stimulate breast cancer growth. 14-17 It appears that the effects of soy may vary depending on menopausal status, the age at which soy is consumed, and type of breast cancer.
Providers prescribe the lowest doses possible to treat your symptoms while preventing side effects. Hormone replacement therapy (HT) is a common treatment for low estrogen, especially during menopause and postmenopause. That being said, only a couple of conditions are FDA-approved for hormone replacement therapy.
However, a few studies suggest that a high intake of isoflavones may cause problems under certain circumstances. Phytoestrogens are found in most plant-derived foods in varying amounts. This hormone is responsible for women’s fertility as well as maintaining feminine body features, but it also plays an important role in men. The benefits of eating these foods mostly outweigh the possible health risks. If you already have diagnosed hormone problems, especially low testosterone or high estrogen, you might want to be more cautious. Your body naturally produces estrogen in small amounts by converting a small portion of your testosterone into estrogen. For instance, the effect of phytoestrogen intake on pubertal development has been poorly studied and could lead to interesting results.

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