Kathy Bowers posted:

>I have a puzzling case in which mom is not producing enough to exclusively
>breastfeed her 10 day old baby. She drinks soy milk daily. I've searched
>the archives expecting to find a relation between soy protein and low milk
>supply because of the estrogen effect. However, I found a reference to
>Sears' Breastfeeding Book (p 75) 'that studies show 30 gm of soy per day
>can increase mother's milk supply 25%' (paraphrased from archive post). Now
>I'm confused. How can exogenous estrogen(ie birth control pills) cause
>decreased milk supply but soy cause increase in milk supply?

I don't know why soy would cause an increase in milk supply; I do know, 
however, that phytoestrogens are weaker than endogenous estrogens 
(including estradiol in pill form) and that they can act as estrogen 
agonists, partial agonists, or antagonists depending on what else is in the 
system.

I did a quick PubMed search on "lactation" and "soy" but nothing jumped out 
with regard to soy's effects on lactation. I didn't look at all the studies 
on cows and pigs though. Soy's effects in pigs might be applicable to 
humans, but the cow's digestive tract is far too different from the 
human's. Not only is the intestinal microflora, which plays a significant 
role in phytoestrogen metabolism, quite different, but cows have more than 
one stomach. (During my kids' first year, I've eaten like I have more than 
one stomach, but that's different! ;-D)

I wonder if the soymilk might not be a red herring. FWIW, I know several 
vegans who consumed quite a lot of soy and had no problems with 
breastfeeding. In searching for clues, how does the rest of the mom's diet 
look?

Good luck and please do post anything you might find out about soy's 
effects on lactation. Thanks!

regards,
Julia

Julia R. Barrett
Freelance Science Writer & Editor
Mom to Sean (6) and Kira (going on 3)
Madison, Wisconsin

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