Soy milk and other soy products contain soy isoflavones, a type of phytoestrogen that might mimic the effect of human estrogen in the human body. Some medical studies have linked soy isoflavone consumption with reduced male fertility, while other scientific research has concluded that soy has no effect on male fertility. No scientific evidence has associated soy milk with sterility in men.
Soy products are the richest dietary source of isoflavones, a type of plant compound with impacts similar to the female sex hormone estrogen in the human body, according to the Linus Pauling Institute at Oregon State University. Isoflavones bind to estrogen receptors in the reproductive organs and in the heart, liver, brain and bones. In some receptors, isoflavones cause the same metabolic effects as estrogen, but in others, soy isoflavones block estrogen and cause an anti-estrogen effect. Soy isoflavones are the subject of scientific interest because a better understanding of how soy isoflavones create estrogenic and anti-estrogenic effects might lead to solutions for estrogen-related health conditions, including breast and uterine cancer and osteoporosis.
Consuming soy foods was linked to markedly lower sperm concentration in the results of a study published in the April 2008 issue of the journal "Human Reproduction." Researchers from the Harvard School of Public Health and Harvard Medical School queried 99 men who had come to the Massachusetts General Hospital Fertility Clinic regarding their consumption of soy foods over the course of three months. The Harvard researchers determined that the men who had consumed the highest amounts of soy foods had 41 million sperm per milliliter fewer than those who consumed no soy products. Sperm motility and morphology were unaffected by the reduced sperm count, and no subject of the study was sterile.
Consuming soy products has no impact on the male sex hormone testosterone, according to a 2008-2009 study published in the American Society for Reproductive Medicine's journal "Fertility and Sterility." A team of researchers from the University of Minnesota, University of Rochester Medical Center and Loma Linda University conducted an extensive meta-analysis of dozens of clinical studies involving soy isoflavones and isoflavone extracts from soy and red clover, which has similar properties. The research team concluded that soy consumption has no significant effect on either total testosterone levels or the amount of bioavailable testosterone circulating for use in the body. Sterility was not in any way implicated in the studies reviewed.
Considerations and Warnings
The New York University Langone Medical Center advises that men with infertility or sexual dysfunction avoid consuming soy products. Consuming large quantities of soy might interfere with certain medications, including the anticoagulent warfarin and the anti-tumor drug tamoxifen, according to the Linus Pauling Institute at Oregon State University. Soy also might contribute to the growth of breast cancer tumors in women. Consult your physician before changing your diet to include large amounts of soy milk consumption or before taking soy isoflavone supplements.