Is Soy really the bad guy??
Soya is commonly answerable for lowering Serum Testosterone levels, Luteinizing Hormone(LH) levels, reducing male Sperm Count and a host of other nasty things.
And there are some studies to actually support this.
Below articles talks about male individuals losing Testosterone levels and LH levels.
https://www.ncbi.nlm.nih.gov/pubmed/17416779
Or
https://www.ncbi.nlm.nih.gov/pubmed/21353476
But, there are many other studies to support the innocence of Soya.
For instance, check this article. It says that Soya DOES NOT ALTER male testosterone levels.
https://www.ncbi.nlm.nih.gov/pubmed/16775579
In addition, there are supportive links like below, that strongly suggests to include Soya in the diet.
https://www.ncbi.nlm.nih.gov/pubmed/22066824
https://www.ncbi.nlm.nih.gov/pubmed/17908338
Also, Soya protein intake enhances muscle protein synthesis and hence increasing lean mass tissue.
With these conflicting studies which side would you pick??
Well, the bottom line is Soya protein taken in Limited Quantities (about a scoop/ 25-30 gms) is okay for muscle growth.
However, taken in excess may affect testosterone levels.
Aditya