If you have questions about whether eating soy is bad, understand that soy-based foods have become popular in nutrition due to their nutritional and health benefits, as well as being great sources of plant proteins. However, there is a common belief that soy reduces testosterone levels and increases circulating estrogen.
This statement is replicated by the fact that soy contains phytoestrogens (isoflavones), compounds with a chemical structure similar to the hormone estrogen. But does eating soy decrease testosterone in humans?
Phytoestrogens and Isoflavones:
As stated earlier, phytoestrogens are compounds with a chemical structure similar to the hormone estrogen. With this, isoflavones can connect to both
ER) receptors, both ERα and ERβ.
In addition, it was theorized that high levels of isoflavones could alter the hypothalamus-pituitary-gonadal axis in men. This change could lead to decreases in testosterone and luteinizing hormone. However, isoflavones differ from estrogen in affinity with receptors for the hormone, as they bind preferentially and activate ERβ compared to ERα. Unlike estrogen, which has equal affinity for both receptors, this difference in binding affinity is important because the two receptors have different tissue distributions and, when activated, exert
even opposite physiological effects.
Effects of soy on reproductive hormones
With this, to analyze whether eating soy is bad, a meta-analysis entitled Neither soy nor isoflavone intake affects male reproductive hormones: An expanded and updated meta-analysis of clinical studies, analyzed whether the consumption of foods derived from soy and isoflavones affected the concentrations of total testosterone, free testosterone, estradiol, estrona and globulin binding to sex hormones.
A total of 41 studies were included in this meta-analysis. These were evaluated for the duration of isoflavone exposure (≤12 weeks vs >12 weeks) and dose (<75 mg/d vs ≥75 mg/d) influence on blood test results.
In conclusion, the study showed that neither the intake of soy, nor isoflavones, regardless of the duration of the research, regarding the dose, affected the levels of total testosterone, free testosterone, Estradiol and estrona. Moreover, most scientific literature does not show that the compounds present in soy when ingested cause significant hormonal changes in humans.
It was seen that soy and isoflavone did not induce any significant changes in testosterone and estradiol. Some potential beneficial effects of isoflavones have been seen such as their obesity prevention effect, blood glucose level reduction effect, reduced risk of osteoporosis and breast cancer.
In addition, soybeans and its derivatives have an antioxidant effect. Furthermore being considered a good source of soybean, it is a good source of unsaturated fatty acids, B vitamins, fibers, iron, calcium, zinc and other bioactive compounds.
Effects Of Supplementation With Soy Proteins Versus Animal Protein
Article: REED, Katharine E.; CAMARGO, Juliana; HAMILTON-REEVES, Jill; KURZER, Mindy; MESSINA, Mark. Neither soy nor isoflavone intake affects male reproductive hormones: an expanded and updated meta-analysis of clinical studies. Reproductive Toxicology, [S .L.], v. 100, p. 60-67, sea. 2021. Available in: