This topic comes into much interest. Thanks to my friend who raised his fear and why he is not a fan of plant based or lets say trust issues such as the womanizing fear from Soya.

Had some good search and tried to simplify this as much as possible. Here we go!

Soybeans are rich in Isoflavones. What is Isoflavones? Isoflavones are also referred as Phytoestrogen. 

In Latin:

PHYTO: Plants
ESTROGEN: female hormone

PHYTO “………” what? That’s the raising concern among males that soy sources can cause feminization due to its estrogen component. Fear of breast enlargement (Gynecomastia) or lowering their testosterone and the associated concerns in the declining sperm count happening worldwide in general.

Phytoestrogens have been investigated over 30 years and are found in plants which are similar to the human estrogen (17-β-estradiol, E2) in chemical structure.

Let's make this MYTH clear and explain why plant estrogens are different than human estrogens.

The phytoestrogens have 5 times higher affinity to the ERβ receptors than ERα. Unlike human estrogen which has similar affinity to both receptors.

ERα: breast tissue, testes, uterus, and kidney.

ERβ: bones, lungs, prostate, urinary bladder, skin, and brain (Plant estrogen binds mainly)

Phytoestrogen in Plants do not function as hormones but as a defense mechanism compound (phytoalexins). For example, they have antibacterial, antiviral, fungistatic and antioxidant effects. They also have a role in fighting against tumors (some data supports its prevention for prostate cancers) and reducing postmenopausal symptoms. (Big topic itself that needs to be addressed separately).

Isoflavones (phytoestrogens) can also be found in chickpeas, beans and minimal amounts in fruits, nuts, and vegetables (1)

In a recent metanalysis (reviewing all scientific studies and analyzing them), published in 2021, shows the following conclusion: (2)
- This Study is the FIRST to examine the effects of soy intake and estrogen effect in men
- Confirms previous data in 2009, 2010 that there is no estrogen effect of isoflavones (Phytoestrogens) in men.
- No effect of soy on semen and sperm count
- Soy Protein leads to similar muscle mass gains and strength in resistance training as animal protein sources (including whey protein)

So, Guys, get this out of your head and dip your sushi in that soy sauce! Also make soy part of your diet through expanding your protein sources with high quality protein!

Hope this helps!

References:

1. Křížová L, Dadáková K, Kašparovská J, Kašparovský T. Isoflavones. Molecules. 2019;24(6):1076. Published 2019 Mar 19. doi:10.3390/molecules24061076

2. Reed, Katharine & Camargo, Juliana & Hamilton-Reeves, Jill & Kurzer, Mindy & Mark, Messina. (2020). Neither soy nor isoflavone intake affects male reproductive hormones: An expanded and updated meta-analysis of clinical studies. Reproductive Toxicology. 100. 10.1016/j.reprotox.2020.12.019