Soy contains phytoestrogens plus phytates, protease inhibitors and other anti-nutrients which block or compromise the body’s uptake of essential vitamins and minerals. This may contribute to nutritional anomalies.
Most notably, the fact that soy is a phytoestrogen means that it has estrogen-mimicking compounds.
Soy-rich processed food items include soy milk, soy-cheese, soy-yogurts, textured vegetable protein and a range of imitation meat products.
Found as soy lecithin & soybean oil, which are both heavily used in the snack food industry.
Worryingly, soy is present in one-third of baby infant formulas in the United States1.
The anti-nutrients in soy such as trypsin inhibitors and phytates block the absorption of minerals such as iodine, zinc, iron, magnesium, copper and chromium, and many others. Minerals such as zinc and magnesium are needed in the production of testosterone.
Consumption of iodine inhibitors, as found in soy, leads to reduced metabolic activity, which may translate into lethargy and a reduced inclination to be involved in physical activity. This reduction in activity will, in turn, lower testosterone levels.
A study by Weber et al. (2001)2 looked into how soy phytoestrogen consumption altered male hormones in rats. The group consuming soy had half the testosterone levels of the control group (260 ng/dL vs 130 ng/dL).
Sharpe et al. (2002)3 conducted a study on baby male monkeys fed with standard cow's milk and soy formula milk. The testosterone levels for the monkeys fed with standard cow's milk were between 280-310 ng/dL. The monkeys fed with soy formula milk averaged 120-260 ng/dL. At the extreme end, that is a 88.4% difference in testosterone levels.
Goodin et al. (2007)4 examined the effects of soy protein on testosterone. They found testosterone levels, on average, to decline by 19% compared to those not consuming soy protein.
Siepmann et al. (2011)5 conducted a study on a healthy 19-year-old male who suddenly began consuming large quantities of soy-based products. The man found that he had a sudden loss of libido and erectile dysfunction. His total and free plasma testosterone levels decreased. All of this was rectified after a year of stopping his vegan diet.
Avoid soy and food containing things like soy protein and soy lecithin.
The pros and cons of phytoestrogens
Link - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3074428/
Dietary soy-phytoestrogens decrease testosterone levels and prostate weight without altering LH, prostate 5-reductase or testicular steroidogenic acute regulatory peptide levels in adult male Sprague–Dawley rats
Link - https://pubmed.ncbi.nlm.nih.gov/11524239/
Infant feeding with soy formula milk: effects on the testis and on blood testosterone levels in marmoset monkeys during the period of neonatal testicular activity
Link - https://academic.oup.com/humrep/article/17/7/1692/576913?login=true
Effect of Soy Protein on Testosterone Levels
Link - https://aacrjournals.org/cebp/article/16/12/2796/260051/Effect-of-Soy-Protein-on-Testosterone-Levels
Hypogonadism and erectile dysfunction associated with soy product consumption
Link - https://www.sciencedirect.com/science/article/pii/S089990071000359X