I don't know about you, but I've felt inundated these past 5 years or so with warnings about the estrogens (phyto-estrogens, mainly isoflavones) in soy foods. Although most studies show the isoflavones in soy to be beneficial - helping fight breast and reproductive cancer, for example - the hype keeps coming.
So I found it interesting to stumble across this study in the American Journal of Clinical Nutrition (September 2010), which found young girls who consumed the most isoflavones entered puberty significantly later than their counterparts who had lower levels of isoflavones.
This makes sense, since plant estrogens, such as isoflavones, act very differently in the body than real estrogen. When our real estrogen levels are high, plant estrogens (or phyto-estrogens) block the cell receptor sites from estrogen uptake, lowering total estrogen levels. This would explain why girls who had higher levels of soy estrogens entered puberty later - as opposed to earlier - than those with lower levels.
In the study, isoflavone levels had no effect on the timing of puberty for boys. To view the abstract of the study for yourself, click here.
So let's all take a big sigh of relief that soy will not cause early puberty in girls, which leads to a higher risk of breast cancer later in life.