For years, weight lifters have done their best to avoid soy protein, and it has been primarily lefts to vegans for an extra protein supplement. The reasons for this is because soy has phytoestrogenicals, which promote estrogen count and thereby inhibit the muscular development sought by other protein sources like whey and eggs. Also, the absorption rate is lower than that of whey, thus making it harder for the body to use it after a work out, when you need it most.

For the estrogen raising point, there have been studies done on rhesus monkeys for years to test the effect soy has on the body (documented at bodybuilding.com). The estrogen count in these experiments have shown that little to no increase was detected. The amount that was increased was not enough to inhibit any sort of muscular growth. Since the estrogen soy exudes is completely different from the human estrogen, it only tends to bind with estrogen receptors if the body is low on estrogen.

One of the few times this occurs is when women are menstruating. The estrogen hits a low, and soy can come in and bind to the receptors, thus bringing some regularity back, and helping to ease the pain and other symptoms during this time. However, for weight lifters or even other people who are not in need of estrogen, and have enough estrogen to fill their receptors, soy will do little to change your levels. So soy is a safe protein for this reason to use after a work out, and for a prolonged amount of use.

When it comes to absorption rate, soy is much slower than whey or albumin (egg). For this reason soy is not quite as good for an after work out protein shake or supplement, because your body is starving for the amino acids and soy will take longer. This could hurt your muscular development, usually not by much, but you will notice slightly better recovery with whey protein.

Should soy protein never be used then? Actually it is still good, but for another reason. On days when you are recovering and not working out, you should have a soy protein shake. Since the absorption rate is slower, it will stay in your body longer and can be there for you when your body needs to absorb it. As where having whey on these days will digest and be gone.

So while not quite as good for a post workout shake, it is still a useful protein source that is good for you and your health. Just use it more during recovery days than workout ones.

Sources:

Information about soy protein located at: http://www.teenbodybuilding.com/todd12.htm

Source: http://www.associatedcontent.com/article/1860267/why_weight_lifters_avoi...