Soy and it's effect on testosterone in men

[TravisGM]

If this has been discussed before on this forum please let me know.

The small amount of research I've done on eating soy and whether or not it effects men's testosterone seems scattered. On the one hand, I've read articles like this: http://www.sciencedirect.com/science...71531706000182

...that show no effect on plasma testosterone in young men taking a soy protein supplement (not the only article I've read, just the only one I care to cite at the moment).

Yet, I've read on countless other sites that talk about a real effect that men should be aware of. They claim things like "if you eat soy everyday you can lower your testosterone levels significantly".

Anyone have any science that points more strongly to one side or the other?

I ask because I'm a vegetarian who avoids soy foods (tempeh, etc.). I don't want to avoid soy if it's not neccessary because it's a good source of protein.
Thanks for any responses!

[DetachedLad]

Might be relevant – http://www.bodyrecomposition.com/res...function.html/

[TravisGM]

Originally Posted by DetachedLad

Might be relevant – http://www.bodyrecomposition.com/res...function.html/

Thanks for citing that.

As said in the article itself...

"The effect of phytoestrogens in men is far less studied and understood. While many are concerned that the phytoestrogens present in soy may negatively impact on testosterone levels the reality is that the studies done to date, using moderate doses of soy/phytoestrogens, have found little to no impact (higher doses are often seen to cause issues)."

AND, most importantly

"Again, I’m not going to focus on all of the potential effects of soy (e.g. on hormones such as testosterone) here; I only want to look at the impact, or potential impact of soy protein on thyroid hormone metabolism."

So I guess now my question would be; how high does the dose of soy need to be in order to negatively impact T levels in men, even a little bit?

[Solis]

In that article and in the protein book, Lyle recommends up to 1-2 servings of 20-25 grams of soy per day, so 40-50 g maximum and 20-25 may be safer.

That's the rough threshold he came to from studies before there are some slight decreases in T levels, and even there 1 study (giving 56 g of soy protein per day to men) was mixed with one subject with very high T levels showing a massive decrease while several others had a slight increase.

[lylemcdonald]

In moderate doses, don't worry aabout it.

[TravisGM]

Thanks everyone!