How does soy affect estrogen levels? Is it safe to let your kids drink soymilk? Nutrition Diva looks at the competing claims and misinformation about soy's effects on children's development.
Nutrition Diva podcast listener Kristin writes,
"My daughter struggles with acid reflux. As an experiment we replaced dairy with soy products to see if it would help. My doctor told us to switch back to dairy because he felt it was not good to give a young girl so much estrogen. I would love to hear your thoughts on this."
Does Soy Contain Estrogen?
Soy does not contain any estrogen. Soy contains isoflavones, which are also often referred to as "phytoestrogens," or plant estrogens, because the molecules are very similar in shape to estrogen molecules. So similar, in fact, that they can fit into specially shaped estrogen receptors in the surface of our cells. Eating soy does not affect estrogen levels in the body, but it may affect estrogen activity in the body - in mostly beneficial ways.
Phytoestrogens Can Block Excess Estrogen
Phytoestrogens may help mitigate the effects of too much circulating estrogen, for example, by occupying some of the estrogen receptors on our cells, thereby dampening the effect of the estrogen. This may explain why soy intake appears to be protective against breast and other estrogen-driven cancers.
Although breast cancers survivors were once told to avoid soy, it now appears that moderate consumption of soy actually reduces the risk of cancer recurrence.
This protective effect seems to be most noticeable in pre-menopausal women, which makes sense because estrogen levels are higher before menopause. And although premenopausal breast cancer is much less common, it also tends to be more aggressive - so it's especially good to prevent it. Further studies have found that soy intake early in life, before girls hit puberty, appears to have the greatest protective benefits.
Finally, although breast cancers survivors were once told to avoid soy, just in case it might have estrogenic effects, it now appears that moderate consumption of soy actually reduces the risk of recurrence in breast cancer survivors.
Phytoestrogens May Compensate for Low Estrogen
At the other end of the spectrum, phytoestrogens may also be helpful for those with too little circulating estrogen, because it can plug into estrogen receptors that would otherwise remain empty. Although the effects of phytoestrogens are extremely weak compared to the effect of human estrogens, it may be enough to ameliorate some of the symptoms and effects of menopause, when natural estrogen production plummets.\
Although the effects are somewhat inconsistent, soy intake can help lessen hot flashes and other unpleasant effects of estrogen withdrawal at menopause. And then, over the longer tem, the isoflavones in soy appear to protect the heart against some of the negative effects of low estrogen levels. Unfortunately, it doesn't look like soy helps much with post-menopausal bone loss.
Of course, it's always possible to get too much of a good thing......