However, in the muscle building department, I don't feel that soy is very useful when used on its own since it is an incomplete protein lacking in the sulfur containing amino acid methionine (which is very important for protein synthesis and immunity) and its Biological Value (a value that measures how well the body can absorb and utilize a protein based on nitrogen retention) is a distant 74 (as opposed to the BV of whole eggs which is 100 and of whey which is 104). Soy is high in branched chain amino acids (BCAAs), however. Therefore, if combined in small quantities with a complete and more bioavailable protein like egg, whey or chicken one can benefit from its high BCAA content.
So is soy bad to achieving your bodybuilding endeavors? Not at all but if you are looking to build muscle, make sure that this is not your main source of protein and be sure to combine it with complete proteins when you ingest it.