In respect to this, does soy inhibit muscle growth?
In short, not only does soy contain lower amounts of the EAAs and leucine, but it may also be responsible for inhibiting growth factors and protein synthesis.
Simply so, is soy protein bad for bodybuilding?
Unfortunately, if a bodybuilder starts to replace too much of the other high quality proteins in their diet with soy, they run the risk of losing muscle due to this lower-quality protein. Approximately 10-30 grams a day of a high-quality soy protein isolate should do the trick for most people.
Some research shows that regularly eating soy products like edamame, tofu, soy milk and miso may cause a drop in testosterone levels. For example, one study in 35 men found that drinking soy protein isolate for 54 days resulted in decreased testosterone levels ( 3 ).