So, should you avoid soy all together for just eat it in moderation? Soy protein has been used to replace animal protein for centuries now, and vegetarians are very quick to point out that soy is a complete protein source - some even say it's better than animal protein. However, for an athlete or middle-aged man looking to raise testosterone levels, it isn't recommended that you eat soy protein. Just for the simple fact that it mimics estrogen and possibly lowers testosterone in the body.
For the vegetarian looking to pack on pounds of muscle, it can be diffiuclt as you don't have many choices for protein. Soy is the only complete protein source that doesn't come from meat or eggs, so you will probably have to stick with soy, but only eat it in moderation - not multiple times a day. There are many other types of beans which contain protein and you might want to eat them as much as possible.
If you aren't a vegetarian and you want to lower your estrogen levels then you should probably consider dropping soy from your diet, as it has the potential to harm your testosterone levels. Stick with whey protein, as it is the best source of protein. Casein protein is also great, especially as a before-bed protein shake. So ultimately, soy protein is inferior to other types of protein and should be avoided at all costs. For aging men who need to keep their testosterone levels optimal, it is not worth it to have all those isoflavones running through your body mimicking estrogen.