Well controlled studies on elite athletes are pretty hard to come by, because nobody wants to go off a routine that is working for them and potentially be set back several months for the sake of science.  The people near the top are hyper-competitive and will do whatever it takes to win.<p>That being said, in addition to the anecdotal evidence that vegans are VASTLY under-represented in the upper echelons of strength and power sports compared with their relative abundance in the general population, there are some good studies comparing muscle protein synthesis following ingestion of whey vs soy protein:<p><a href="http:&#x2F;&#x2F;jap.physiology.org&#x2F;content&#x2F;107&#x2F;3&#x2F;987.short" rel="nofollow">http:&#x2F;&#x2F;jap.physiology.org&#x2F;content&#x2F;107&#x2F;3&#x2F;987.short</a>
<a href="http:&#x2F;&#x2F;ajcn.nutrition.org&#x2F;content&#x2F;86&#x2F;2&#x2F;373.short" rel="nofollow">http:&#x2F;&#x2F;ajcn.nutrition.org&#x2F;content&#x2F;86&#x2F;2&#x2F;373.short</a>
<a href="http:&#x2F;&#x2F;www.biomedcentral.com&#x2F;content&#x2F;pdf&#x2F;1743-7075-9-57.pdf" rel="nofollow">http:&#x2F;&#x2F;www.biomedcentral.com&#x2F;content&#x2F;pdf&#x2F;1743-7075-9-57.pdf</a><p>There is also some data suggesting vegans have slightly lower free testosterone and free IGF-1 than omnivores too, though at the highest levels rampant steroid use probably makes this a moot point.