The Truth About Soy + Fertility, Man Boobs + PCOS
In the second post in my series on the health effects of soy, we’re talking about soy and fertility, PCOS, acne, and so-called “man boobs.”
Welcome to the second post in my three-part series on soy!
If you missed last week’s post, The Truth About Soy + Cancer, be sure to go back and read it (or watch the video) so that you have all the info you need to understand the rest of the soy series.
As we discussed last week, soy is a very controversial food.
However, what we learned last week is that when it comes to soy and cancer, there really shouldn’t be any debate – studies consistently show that soy consumption prevents + fights many cancers.
Today, we’re talking about another hot-button issue surrounding soy – fertility.
Soy and Fertility
Fears about the effects of phytoestrogens on fertility were initially sparked in the 1940’s by the observation that sheep eating large amounts of red clover, a phytoestrogen-containing plant, developed infertility.
Remember, phytoestrogens, specifically, isoflavones, are the chemical compounds found in soy and other plants, that actually possess cancer-fighting properties.
Subsequent animal studies supported the observations in sheep, showing that high levels of phytoestrogens from a variety of sources also affected reproductive functioning.
Studies in mice show that injecting baby mice with high doses of the bioactive phytoestrogen genistein impaired fertility.
However, as we learned last week, the human body does not process phytoestrogens in the same way that animals do and the effects seen in animals are likely due to far higher blood concentrations of these compounds than those reached in humans.
Injecting baby mice with high-dose isolated isoflavones can hardly be compared to the consumption of a moderate amount of whole soy food, by an adult, orally, which requires digestion, absorption, and activation of the isoflavone.
In human females, there is absolutely no evidence that soy consumption impacts fertility. In fact, a recent study of women undergoing IVF showed a 77% increase in the chance of achieving a live birth for women who have a high intake of soy products.
Another randomized controlled trial of couples undergoing infertility treatment showed an increase in live birth rates for those consuming isoflavone supplements.
Alternative health practitioners also frequently advise patients with polycystic ovarian syndrome a common cause of infertility to avoid soy.
However, studies show that soy may actually be beneficial for those with PCOS.
A recent randomized controlled trial of 70 women with the condition showed improved markers of insulin resistance, triglycerides, and oxidative stress which are all believed to contribute to the progression of this disease.
Soy and Men’s Fertility
The effect of soy on men’s fertility is also a common topic of misinformation.
I can’t tell you the number of concerned guys that have asked me whether eating soy will give them man boobs.
Spoiler alert – the answer is NO.
While a couple of poorly done studies with small sample sizes and no control groups found slight decreases in circulating testosterone following consumption of soy products, the bulk of the scientific research has shown absolutely no effect.
A recent meta-analysis of 32 human studies found no changes in testosterone or other sex hormones following consumption of soy or soy products.
Other studies support this showing no impact of dietary phytoestrogens on male reproductive function.
Soy and Acne
Now, the next claim is kind of funny, considering it directly contradicts the previous claim.
Some people say that soy actually increases testosterone by decreasing production of estrogen, which then causes acne.
This is also unsurprisingly not true. There are absolutely no studies suggesting this to be the case.
In fact, soy may actually reduce acne by helping to stabilize blood sugar. High blood sugar levels and insulin resistance are associated with acne.
A recent randomized controlled trial in obese women showed that soy protein helped improve insulin sensitivity to a greater extent than the same amount of protein from meat and dairy.
So, as you can see, the claims that soy affects sex hormones and increases the chance of male or female infertility, PCOS, or acne are clearly unsupported by science.
And that’s it for today’s topic!
In the next and final video of our soy series, I’ll be tackling an issue that is a lot less cut and dry: soy and thyroid health.
There are claims that soy negatively impacts thyroid hormones and leads to hypothyroidism and we’re going to explore those next time. In the meantime, if you missed the first video in this series on soy and cancer, be sure to check it out.
And make sure you SUBSCRIBE to my YouTube channel so you don’t miss the next video!
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Weigh In: Have you heard these claims about soy and fertility? Do you know any guys who are afraid that soy causes “man boobs?!”
amanda -runtothefinish says:
Thank you so much for this!!! First because I laughed but mostly because we have to stop rotating demon foods!
Here’s something you could add to your post: when my husband and I were trying to get pregnant the second time around, we were strict vegetarians. We ate no meat and relied on a lot of soy (tofu) for our protein needs. It took us a year and then we started getting worried. We did a bit of research and came across the soy + male infertility blurbs, and decided to ditch the tofu for a while. Sure enough, within a month or so of no soy products, we got pregnant. Coincidence? We will never know. ;)
Jessica Levinson says:
Great post! Thanks for getting the truth out about this topic!
Alisa Fleming says:
I was so giggling my way through this post with those pics. Love the man “bro” pic. I love the contradicting studies – it’s such an issue with the anti-soy claims.
I have heard so many different things about eating soy! I love edamame and occasionally tofu! So we just practice moderation when it comes to consuming soy around here! But LOL to the man boobs!
Tara | Treble in the Kitchen says:
I absolutely love your scientific breakdown!! :)
Taylor Kiser says:
Great information to help set the record straight! Thanks for posting!
Emily Kyle says:
(Raising my hand) Also literally LOLing at man boobs! But seriously, love love your YouTube videos and your always awesome evidence based approach, you’re amazing Whit!
Whitney E. RD says:
Thank you so much, Emily!! Glad I could get a laugh out of you :)
This is SO interesting, haha! I love that you’re knocking out all of these myths and bringing clarity to all of the debate. Especially love how you break it all down!
Brianna Jj says:
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