Is soy milk bad for men?

Isoflavones (components of soy) have been a part of the diet in different populations for centuries. They belong to a class of compounds known as phytoestrogens due to their structural and functional similarities to human estrogen. The consumption of soy protein in the diet has been reported to have many health benefits; however, due to its estrogenic qualities, many theories have been suggested regarding the negative hormonal effects in healthy men (e.g. increasing estrogen levels).

Two studies tested this theory (Habito et al, 2000 and Mitchell et al, 2001) and found that soy intake did not have a significant effect on estrogen levels in men. Therefore, at this time it appears safe for men to consume normal quantities of soy protein and soy products (1-2 servings daily if desired as part of a meal). Additionally males in many different cultures have been consuming large quantities of soy for centuries with no signs of estrogen-related problems.

Whether or not drinking soy milk affects hormone levels in men is a tough question.  If you're just drinking soy milk and only get a little bit of soy in your overall diet, it may be beneficial.

Soy is a phytoestrogen. Your body treats certain molecules in soy like estrogen. In men, estradiol (a form of estrogen) is associated at a certain level with being heart healthy. Just don't go overboard. In moderation, soy is absolutely fine. However, if you're drinking soy shakes and have a high soy protein intake, then that might be starting to push the edge.

High estrogen levels cause lower testosterone levels.  An estrogen-testosterone imbalance in men can affect sex drive.  You must eat a lot of soy to affect that estrogen balance, however. I don't recommend cutting all soy out of your diet.