There is no evidence that men who eat moderate amounts of soy experience any feminizing effects, which is what I am guessing you are concerned about. Certainly we don’t see these effects in cultures where daily consumption of soy is common.

There is some evidence that vegetarian men have somewhat lower blood testosterone levels than omnivore men. There are several possible explanations for this. Soy consumption could certainly be one of them but the evidence for this is not very clear. The higher fiber intake of vegetarians could also affect testosterone levels. Also dietary fat and obesity increase testosterone levels and vegetarians tend to eat less fat and be slimmer.

But before you bolt for dinner at the nearest steakhouse, let’s put this into perspective. There is no evidence that vegetarian men have testosterone levels that are too low. There is a range of what is normal and as long as you are in that range, there is no advantage to being at the higher end of the range. In fact, being at the lower end of the normal range could have benefits. For example, lower testosterone levels are associated with reduced risk for prostate cancer in some studies. And, not surprisingly, there is evidence that consuming soy reduces risk for prostate cancer. This compares to the situation in women. Evidence suggests that vegetarian women have lower estrogen levels–perhaps for the same reasons noted above for testosterone. And this might help to protect against breast cancer.

Because the average American is a meat-eater, we have a tendency to base our ideas of what is normal or optimal based on what occurs in meat-eaters. Of course, we know that for many things this is not true. For example, "normal" cholesterol levels–the levels typically seen in meat eaters–are too high for good health. The situation for testosterone may be similar. Judging these levels based on those that occur in people eating an unhealthy diet doesn’t make sense.