I have read it and heard it in several places.
Soy beans have an active ingredient known as isoflavones, that has estrogen like properties. It slows muscle growth and reduces sperm count among men.
I would like other knowledgeable members to shed more light on this one.
I am a very voracious meat eater. My day starts with a pound of beef with barbeque sauce and ends with three to four whole chicken breasts. I have seen amazing results. My bench presses have more than doubled and I feel really active and energetic.
I never saw this difference when I briefly used soy protein.