There have been studies that show high concentrations of estrogen-like compounds in soy-based products. People trying to maximize their testosterone levels while ingesting high amounts of protein are generally advised to stay away from soy

Edit: here's an article from a bodybuilding website that tries to summarize the conclusions of various journal articles on the topic:

https://www.bodybuilding.com/fun/ivan3.htm

What about the actual bovine estrogen in any milk product?

Edit: Here's a link to an article discussing how much soy is too much: https://nutritionfacts.org/2013/02/19/how-much-soy-is-too-mu...

For what I know that effect is negligible. Here's a review of some studies on the topic:

https://nutritionfacts.org/video/who-shouldnt-eat-soy/

See my other comment on T-level being higher in vegans (Even higher then in vegetarians). There's a huge vegan-fitness movement going on, and it rapidly moving into professional sport in general. They simply self-report to perform better, thus stick to the diet.

This article basically says soy protein is great.

I don't agree that soy is bad for you, I was just trying to give the parent comment a reason why others might find issue with it.