Phytoestrogens from plants are similar to the body’s own estrogen. Depending on the type of phytoestrogen, however, the efficiency is 100-10,000 times lower. Nevertheless, due to their structural similarity, they can also dock to estrogen receptors in various tissues of the body and develop a very weak estrogenic effect there.
Does soy consumption therefore lead to feminization in men?
In the past, two negative individual case reports due to excessively high continuous intake and negative effects in animal studies led to the repeated occurrence of the thesis of feminization in men. It is a fact that soy does not have any negative effects on testosterone levels, sperm quality and other fertility parameters when consumed in normal quantities (1). Paracelsus once said: All things are poison, and nothing is without poison. The dose alone makes a thing not a poison.
Does soy consumption lead to problems with the thyroid gland?
Although soybeans, like many other foods (e.g. broccoli, cauliflower, kale, etc.), belong to the food group with potentially goitrogenic (thyroid enlargement) properties, soy has no effect on the thyroid function of healthy people. Provided there is a sufficient supply of iodine.
Nice to know:
- None of the major nutrition or cancer societies (BDA, DC, AAP, CCA, AICR, ACS, BfR, DGE) advise against the consumption of soy products.
- Genetically modified plant foods (soy, corn, rice, rape, pea, sugar beet, papaya, pumpkin, potato, etc.) are excluded. In Europe, however, these must be labelled by law. Animal foods are less transparent in this respect. I.e. there is no law which specifies a label. Consequently, there is the possibility that the animals have received genetically modified feed and this can lead to negative complications in humans. Only in the case of organic products is there a corresponding ban on feeding genetically modified feed (4).
- Many soy-critical reports come from US-American authors. The soya situation in the USA cannot currently be compared with that in Europe (90-100% of the soya cultivation area in the USA is genetically modified).
- Anti-soya stories can be traced back to a single group in the USA called the Weston A. Price Foundation (WAPF). The foundation is known for its positive attitude towards the consumption of saturated fats and cholesterol from traditional foods, for supporting local foods and farms, for its rejection of veganism and some aspects of vegetarianism. “Most of these things are anecdotal, untrue or based on inadequate animal experimentation” (Butler, 2010). “If you read it on WAPF, it’s probably wrong” (Hall, 2015).
- Animal experiments are not meaningful. These are different organisms and metabolic effects. They are therefore not transferable to the human body.
- Mitchell, J.H., Cawood, E., Kinniburgh, D., Provan, A., Collins, A. R. & Irvine, D. S. (2001). Effect of a phytoestrogen food supplement on reproductive health in normal males. Clin Sci (Lond), 100(6), 613-618
- Kulling, S. E. & Watzl, B. (2003). Phytoöstrogene. Ernährungs-Umschau, 50(6), 234-239.
- Taku, K., Melby, M. K., Kronenberg, F., Kurzer, M.S. & Messina, M. (2012). Extracted or synthesized soybean isoflavones reduce menopausal hot flash feqnecy and severity: systematic review and meta-analysis of randomized controlled trials. Menopause, 19(7), 776-790.
- Neuerburg, W., Schenkel, C., Haccius, M., Hoffmann, U., Langerbein, ,R., Neuendorff, J., Reiners, E., Schmidt, H., Schumacher, U. & Winkel, S. (2013). EU-Verordnung Ökologischer Landau: Eine einführende Erläuterung mit Beispielen zu Erzeugung, Kontrolle, Kennzeichnung, Verarbeitung und Einfuhr von Öko-Produkten – Mit allen Gesetzes- und Verordnungstexten (4. Aufl.). Ministerium für Klimaschutz, Umwelt, Landwirtschaft, Natur- und Verbraucherschutz des Landes Nordrhein-Westfalen, 10.