I was a vegetarian for about 12 years.  I didn’t expect to keep up that self-imposed dietary constraint when I went off to college.  But, alas, I found myself in vegetarian heaven – Ithaca, NY.  Lets just say, ever since then, I love my tofu.

So after a healthy dose of soy last night, it occurred to me –
“Oh, crap, soy = phytoestrogens.”

Quick definition:  phytoestrogens are plant-based compounds that have a similar structure to the estrogens that our own endocrine system produces.  This similarity allows such compounds to go galavanting around, hitting up the estrogen receptors strategically placed throughout our bodies, mimicking estrogen or blocking our own estrogen.  This is not actually entirely a bad thing in adults – there is quite of bit of research coming out showing the beneficial properties of phytoestrogens on aging and cancer and alleviating other health problems.

Back to my pregnancy question.

What is the protocol for eating (or not eating) soy during pregnancy?  Am I dosing the seahorse (our affectionate nickname for the growing fetal form) with estrogenic compounds and screwing with the development of this little thing’s reproductive system? Its reproductive behavior? All the other developing systems that are primed and ready to respond to an estrogenic signal?

First, to Google where this gem rose to the top:
http://healthybabycode.com/5-myths-about-pregnancy-nutrition-4-soy-is-a-healthy-alternative-to-meat-dairy

Ugh, really? If you didn’t click on the link, don’t bother.  The post is USELESS.  The papers they cite are OLD and have NOTHING to do with eating soy during pregnancy.  Just scary points from studies dosing up babies with soy formula. And, no, I didn’t even bother clicking through the “For a thorough discussion of the dangers of soy products…” link.

Ok, onto the scientific literature.

I searched quite a bit and wasn’t completely satisfied with what I found.

In one paper by Yu et al. published in Behavioural Pharmocology in 2010, the researchers found a masculinizing effect on female behavior for those females exposed to phytoestrogens in utero.

Another paper from 2002 by Klein et al. in Molecular Medicine showed increased spleen and thymus weight for male rat pups born from mothers fed super high concentrations of phytoestrogens.  They also found lower testosterone in the male pups even if their mother rats were fed low doses.
Uh oh.

But, wait, these are rats.  Rats fed chow laced with the compounds being studied.  They have no other choice than to eat this every day.  What about humans?  On a normal human diet?   Even I don’t eat tofu every day!

I found the most promising data set in a 2012 paper by Jarrell and colleagues published in Obstetrics and Gynecology International. The researchers were mainly interested in the overall presence of phytoestrogenic compounds that could reach baby from mama.  They measured phytoestrogen content in the amniotic fluid during pregnancy and in umbilical cord blood and mother’s plasma at birth.

Phytoestrogens were detectable in the cord blood but at concentrations 3x lower than levels in the mom’s plasma.
But this measurement includes all women measured, whether or not they were active soy-eaters.

For those mamas who disclosed their soy intake, only those eating soy on a daily basis showed any difference in the amniotic fluid as compared to the pregnant ladies who claimed to never eat soy (no comparison shown for cord blood).  Even those mamas who ate soy on a weekly basis showed absolutely no difference from the I-never-eat-soy group.   A 24 hour clearance? A limited ability of the phytoestrogens to build up in the amniotic fluid with reduced intake?  For future research to determine….
Also important to note, ALL the pregnant women, even those in the I-never-eat-soy group, had measurable amounts of phytoestrogens in the amniotic fluid.  The cord blood data suggests the same since it is impossible to tease out who is who from the data provided.

So, even if you don’t enjoy a good tofu pup every now and again, you are probably still getting some soy sneaking into your diet.

Interestingly, those mamas carrying female nuggets had higher phytoestrogen content in the amniotic fluid than those carrying male nuggets.  How that one works out physiologically is still a mystery.

My take home from this – Unless you manage to eat that tofu just at the precise moment when an estrogenic spike would screw up a key estrogen dependent fetal programming step, you are probably in the clear.

On the positive side of soy consumption – A 1998 paper from Fritz et al. in Carcinogenesis found that rat mothers chowing on a “physiological dose” of a phytoestrogenic compound actually conferred benefits to their daughters.  Female rat pups dosed in the womb had reduced susceptibility to developing cancer in their mammary tissue.  In humans this could translate to decreased risk of breast cancer!

Advice to myself – I will keep eating tofu… in moderation.