i know alot of vegan bodybuilders who rely solely on soy as their protein source whether as a food or as a supplement i.e isolate etc and have no side effects.
Yes, and they avoid the antibiotics and hormones often given to the cattle as well as the uric acid and lactate trapped in the meat and the uric acid formed from its breakdown. In addition beef presents the problem of possibly getting too much iron if eaten in excess since heme iron is more readily absorbed than plant irons, and men and non-menstruating women in particular do not have a normal means of ridding the body of excess iron.
When I used to race eating beef would totally wipe out my energy after just a few days. So tried to avoid it as much as possible.
The body is not designed to eat large amounts of meat. I have heard numeorus times that it takes about 3 days for a piece of beef to break down in the digestive system. Again the diet of our early ancestors was primarily plant material, not meats. In fact, if all our ancestors ate was meat then what was feeding their beneficial intestinal flora since they feed on fibers?