Soybeans contain chemicals called isoflavones, some of which can mimic the effects of estrogen, the predominant female reproductive hormone. You may worry that consuming too much soy can flood your body with estrogen and stifle your testosterone levels; however, most scientific research points to this as an unfounded fear.
Phytoestrogen
Some of the isoflavones present in soy are known as phytoestrogens. Phytoestrogen is a plant chemical but actively bonds with estrogen receptors on your cells to perform functions like human estrogen. This does not mean that eating soy will cause an overstimulation of estrogen cells in your body by these chemicals, however. Phytoestrogens regulate their own function, acting as additional estrogen if you have a deficiency. If you have sufficient estrogen, the isoflavones in soy have a limited effect.
Comprehensive Research
Soy’s potential effect on male testosterone levels is an area of considerable scientific research. A 2002 meta-analysis of soy’s effect on men in the “Journal of Nutrition” found that all large-scale studies have shown no reduction in testosterone after consumption of soy foods. Though some animal trials demonstrated that soy reduces testosterone, these results were attributed to differences in mammalian physiology. A second meta-analysis in a 2010 issue of “Fertility and Sterility” had similar findings, stating that soy does not affect “total or free testosterone levels” in men.
Erectile Dysfunction
As the leading male hormone for sexual reproduction, testosterone can affect your sexual drive and ability to achieve an erection. Columbia University states that phytoestrogens in soy do not affect the ability to achieve an erection for most men. However, a 2011 case study of a 19-year-old male in “Nutrition” demonstrated that prolonged consumption of soy foods in high quantities may lower testosterone for some individuals. The man in the study had Type 1 diabetes and consumed a vegan diet. After he discontinued the high-soy diet, his testosterone level returned to normal and he regained full sexual function after one year.
Soy Formula
Much like adult males, soy foods do not appear to affect testosterone levels in children. The Linus Pauling Institute of Oregon State University reports that as much as 25 percent of infant formulas in the U.S. contain soy, but at least six clinical trials have never found soy formulas to have a negative effect on infant hormones or growth. Even a retrospective study of 811 adult men and women fed soy formula showed no difference between their growth and time of puberty compared to adults that had been fed cow’s milk formulas.
References
- New York University Langone Medical Center: Isoflavones
- Columbia University; Soy Products and Male Impotence; May 2006
- Linus Pauling Institute; Soy Isoflavones; Jane Higdon, Ph.D.; January 2006
- "Nutrition"; Hypogonadism and Erectile Dysfunction Associated with Soy Product Consumption; T. Siepmann, et al.; July 2011
- "The Journal of Nutrition"; Hormonal Effects of Soy in Premenopausal Women and Men; Mindy Kurzer; March 2002
- "Fertility and Sterility"; Soybean Isoflavone Exposure Does Not Have Feminizing Effects on Men: A Critical Examination of the Clinical Evidence; M. Messina; May 2010
