Whey vs Soy... have we been tricked?

[robin1]

@UKcheetah

Daidzein is a key isoflavone found in soy that acts as a potent phyto-estrogen. It is structurally a very weak “pseudo-estrogen” (about 1000 times weaker than the body’s primary estrogen estradiol). This is good news to the bodybuilder because weak estrogens like daidzein will compete with stronger estrogens like estradiol for available receptor sites to “bind” to. By binding to the receptor sites daidzein then “blocks” the stronger estrogens from binding to and activating receptor sites. With the daidzein isolflavone attached, estrogen receptor sites remain inactive. This inactivity further minimizes the negative effects of estrogen in the body. Many researchers believe this effect is the reason soy protein is linked to a reduction in the risk for many forms of breast, endometrial, and prostate cancer. This mechanism works similarly to the prescription drug Nolvadex (tamoxifen citrate)–an anti-estrogen staple in the bodybuilding community.

I don’t get this argument. If daidzein is 1000 times weaker than normal estrogens this would be because it binds 1000 times weaker to the estrogen receptor, in which case it would not be able to outcompete endogenous estrogens (unless present at 1000-fold higher concentrations). If there is anything to this theory than it must be more complex than that. Even if this blocking effect is true, however, it would likely result in increased production of endogenous estrogens due to blocking estrogen receptor mediated negative feedback mechanisms (i.e. the body would ‘think’ it doesn’t have enough estrogens and thus produce more).