Why is regular consumption of soy harmful?

Research indeed indicates that regular consumption of large amounts of soy — especially in the form of isoflavones (plant phytoestrogens) — may have an epigenetic effect, meaning it can alter gene expression without changing the DNA itself. These changes can be passed on to the next generation, and in some cases manifest in the second or third generation, including as fertility issues.

Mechanisms of Action

Phytoestrogens (Isoflavones). Soy is rich in isoflavones, particularly genistein and daidzein.

They act as weak agonists of estrogen receptors, primarily ERβ. With high and regular consumption, these compounds can interfere with the hormonal balance of the body, especially during critical periods of development — in utero and early childhood.

Disruption of Reproductive System Development. In animals exposed prenatally to phytoestrogens:

• disruption of ovarian or testicular formation is observed,
• sperm motility and overall count decrease,
• in females — the cycle is disrupted, and sensitivity to their own hormones changes.

Epigenetic Inheritance. Phytoestrogens can alter DNA methylation, histone modifications, and microRNA levels in embryonic cells. These changes:

• are preserved during cell division,
• do not disappear with age,
• can be passed on to subsequent generations.

This mechanism explains why infertility or reduced fertility may not manifest in the first generation but become pronounced in the second or third.

What Studies Show

Mouse Models: In mice receiving high doses of soy isoflavones, a decrease in fertility was observed in F2 and F3 offspring. In males — a decrease in testosterone and worsening of sperm parameters.

Human Observations: In women consuming large amounts of soy during pregnancy, changes in reproductive function in daughters are sometimes recorded (for example, later onset of menarche or changes in the cycle).

However, the evidence base in humans is currently weaker than in animal studies.

Conclusion

The issue is not with soy as a product, but with the dose and frequency of consumption, especially in isolated forms — for example, soy protein, soy isoflavones in supplements, soy milk every day, etc.

This can create a cumulative effect of phytoestrogen exposure, especially during critical periods of development (in utero development, early childhood), and over time pass on the risks of infertility to offspring.

Thus, moderate consumption of soy products — especially traditional ones (tempeh, miso, natto) — does not pose a risk. The problem arises with excessive and chronic consumption in isolated forms.