There is increasing media attention on the effects of soy, which has become evermore pervasive in our modern diets, on our endocrine systems. Specifically, there is a claim that compounds present in soy and soy-derived products like tofu, soymilk, and tempeh, mimic estrogen in the human body and might lead to undesired health consequences.
What's in Soy That's Estrogen-Like?
Compounds like genistein and daidzein that naturally occur in soybeans and other beans are part of a class of molecules called isoflavones. They are phytochemicals, meaning they are chemicals produced by plants, and they also act as antioxidants, in that they accept singlet oxygen, a destructive free radical that can damage living tissue.
Isoflavones are also classified as phytoestrogens, which means they are plant-derived materials which act like estrogen. They bind to estrogen receptors in a wide variety of tissues, in both male and female, similar to estrogen. Isoflavones are about 0.1-1% as potent as estradiol, natural estrogen (Molecular Pharmacology)
There are two types of estrogen receptors: alpha and beta. Alpha receptors can be found in tissues such as the ovarian stroma and breast cancer cells in women, the efferent duct epithelium and in male testes. Beta receptors are found more broadly in such organs and tissues as the kidneys, brain, and blood vessel endothelium in both men and women. Genistein and daidzein tend to have a higher affinity to beta receptors than alpha receptors (Endocrinology).
Are Phytoestrogens Just Like Estrogen?
Phytoestrogens do not act exactly like estrogen, but because they bind to the same estrogen receptors as estrogen but act more weakly, they can have certain effects on the body. When estrogen levels are high, soy isoflavones can lower estrogenic effects, by binding to receptors and preventing the more powerfully-acting estrogen from binding to them. Similarly, when estrogen levels are low, isoflavones bind to estrogen receptors and can exert some estrogenic activity where there wouldn't be much otherwise.
Why Are Soy Products Suggested for Menopause?
This is why soy products are suggested for menopausal women: their isoflavones can deliver a more stable estrogenic response in the body than wildly-fluctuating natural estrogen levels women experience after menopause.
Do Soy Isoflavones Pose Any Health Threat to Women?
The research so far has pointed to isoflavones showing both helpful and harmful effects on women's health. Here's what studies have suggested so far.
Good for women's health:
- Helps maintain bone density (reduces risk of osteoporosis)
- Provides some relief from menopausal vasomotor symptoms (hot flashes)
- Helps inhibit certain types of cervical and breast cancer (and other types of cancer, not limited to women)
Bad for women's health
- Might promote breast cancer via different pathways (the genesis and proliferation of breast cancer involves a complex system of mechanisms, some of which might be accelerated by isoflavones)
- Can decrease the effectiveness of letrozole and tamoxifen, two popular treatments for breast cancer
What About Men?
"Estrogen" is not something that men like to associate with their own health, even though men do produce (much smaller) amounts of estrogen, and phytoestrogens like soy isoflavones are not human estrogen. However, controversy on the effect of substances like genistein and daidzein on men has continued to rage, and the contradictory nature of the effect of these substances on the complex balance of male hormones has led to people both cheering and booing soy in men's diets.
The weak estrogenic effect of phytoestrogens suggests a more "feminizing" effect on men who have lower serum estrogen levels than on those with higher serum levels of female hormones, similar to the effect seen in women. Lab studies have shown that genistein induces apoptosis (cell death) in testicular cells, although in a dosage-dependent manner that might not implicate soy for men who consume it in moderation. Another study showed no observable effect on men's endocrine levels or semen quality after consuming soy for 2 months. This was the conclusion of a fairly extensive meta-study: no effect of isoflavones on men's testosterone or other reproductive hormones. Another study confirmed this but pointed to a cognitive ability increase among soy-eating young men.
So What To Do? Eat Soy or Avoid It?
The jury's still out whether soy has a net positive or net negative benefit on health, so it might be understandable—maybe even wise—to moderate your consumption of soy products until more research is done. Remember when margarine was considered much healthier than butter because it lacked cholesterol? Hopefully, future research will not be quite so damning of soy; at least it's a natural food, having been consumed by Asian populations for thousands of years.
In the meantime, you can take a look at a chart that I put together listing common soy-based foods, from the least-processed to most-processed forms, with the amount of genistein and daidzein per serving. Generally, processing tends to reduce isoflavone levels, partly the result of "diluting" the soy component with other substances such as wheat gluten, starches, filler, and flavorings.
edamame (fresh soybeans)
soynuts (roasted, dried soybeans)
veggie hot dog
2 hot dogs
This content is accurate and true to the best of the author’s knowledge and does not substitute for diagnosis, prognosis, treatment, prescription, and/or dietary advice from a licensed health professional. Drugs, supplements, and natural remedies may have dangerous side effects. If pregnant or nursing, consult with a qualified provider on an individual basis. Seek immediate help if you are experiencing a medical emergency.
peachy from Home Sweet Home on August 17, 2020:
Lots of information given, thsnks for the hub.
I heard from doctors that eating soya based products reduces risk of osteoporosis especially over 40s women
J bea on September 21, 2019:
Allergic to Soy. Hives & throat closed.
DeeDeeLaRochelle on September 03, 2017:
Very informative article!
Emily Tack from USA on November 17, 2014:
Very informative article, livelonger. Tofu and I don't seem to "get along" very well, but tempeh is a different story. My body seems to thrive on it, and my conjecture is that it is because tempeh is a fermented food.
I enjoyed reading this, and shall bookmark it for future reference.
Jason Menayan (author) from San Francisco on September 04, 2012:
Thanks, CC! I was happy that they weren't too high in tofu, also, since I like the taste of tofu (but I don't eat as much of it as I used to).
Cynthia Calhoun from Western NC on August 30, 2012:
I've been eating A LOT of tofu lately - for a hub I'm writing, haha - but it's good to see that the genistein and daidzein aren't that high in tofu. This is something I often wonder about - I'm glad I came across your hub. Nicely done and well-researched. Thank you for sharing this.
Melis Ann from Mom On A Health Hunt on February 22, 2012:
Thanks for this hub - very informative. It answers many of the current questions I think many people have swirling around them regarding soy. As with any food controversy, too much of anything isn't good for you. There are probably some benefits, but if your diet is heavily weighted in soy products, then you're probably tipping the scale toward unhealthy. I'm sharing this one. Thanks!
SanneL from Sweden on December 05, 2011:
This is a great hub! You have put so much work into it.
I tend not to eat soy products, since I do not consume anything pre made, and soy-products are most of the time processed food.
However, if I had to choose tofu over meat, I would definitely go for the tofu.
I believe if we eat and drink everything in moderation, we don't have to worry.
Jason Menayan (author) from San Francisco on November 16, 2011:
Thank you, all, for your comments!!
Carolyn Sands from Hollywood Florida on November 11, 2011:
Great information and very much appreciated. I can tell you really did do your research. I've been turning away from meats. I eat a lot of beans instead. Was considering the soy products also, but now I don't know...
Liz Elias from Oakley, CA on November 10, 2011:
Very interesting, indeed.
I hate it when the medical researchers can't make up their minds, and contradict their own studies... oh..it's beneficial/oh..it also poses a risk. Come on, folks..you can't have it both ways.
Every day's news seems to come up with something that's bad or good for us...and that contradicts something that's been preached for years, then turn around and switch it back again.
In the end, I just eat what I like, (in moderation, which is actually the key, here...), and figure I may as well enjoy my life and my food while I'm here, because one thing about life is certain: you don't get out of it alive!
So I don't stress over this kind of information that changes every other week except on the third Tuesday following a blue moon in winter on leap years.
Voted up and interesting.
plinka from Budapest, Hungary on November 10, 2011:
I like this hub. I usually eat tofu with miso soup, it's very healthy. Isoflavones are said to control bad cholesterol level as well, maybe because low estrogen level can cause the increase of cholesterol level. To tell you the truth, I don't believe that isoflavones trigger breast cancer if you eat meals moderately in general. In Asian countries there are less people who suffer from cancer. Great hub! Voted up!
Deidre Shelden from Texas, USA on November 10, 2011:
A nutritionist working with me to reduce affects of food sensitivities on my fibromyalgia is having me start on some soy products. So this caught my eye. I wonder now if this is good, since I'm carrying so much extra estrogen around in my "extra" fat!
Shari from New York, NY on November 10, 2011:
I have never been a huge fan of soy. Actually when I see products with 'soy' I get somewhat turned off. I have never liked margarine (looks like plastic) and always opt for butter, but in moderation, which is what I think we should do with anything we eat. Im a true believer that balance is the key and rather go with to go with the natural product! Great information here and like Simone I love the chart!
Wesman Todd Shaw from Kaufman, Texas on November 10, 2011:
I'm more inclined to the Paleo diet - too many un natural things in modern foods.
That said, I sometimes enjoy a glass of silk - simply because it tastes so good.
India Arnold from Northern, California on November 10, 2011:
This hub has it all, outstanding information on the soy estrogen debate. I learned sooo much by reading this. I don't eat a ton of soy, but I do use a soy based cream for hot flashes --getting old is h*ll, but far better than the alternative. The Soy cream seems to help me...um...and those around me. ;) This is one for bookmarking LL. Thanks for such a thorough presentation; and that chart is right in my wheelhouse, LOVED IT!
Shalom and HubHugs of course~
Lorna Lorraine from Croydon on November 08, 2011:
This was a well explained hub. I have considered returning to soy milk because of how well they contained my hot flashes. I believe it is safe and beneficial in the amounts that I use. Other than tofu, those are the only soy products I continue to consume.
Jason Menayan (author) from San Francisco on November 06, 2011:
Thank you, everyone, for your comments.
Simone: Yeah, when you look at the research, it looks like phytoestrogens have an impact on an incredibly complex endocrine system that we still haven't figured out. It's hard to say if it's a net-positive or a net-negative, and that would depend on whether you're talking about men or women, and at different stages of your life.
Claudia: Now I wish I had entered that as an option!
Lily Rose: I'm very glad that you've conquered cancer, and I can certainly understand your and your oncologist's ambivalence about soy. I hope the research continues so we can understand soy's impact on the body fully, and so solid recommendations can be made. My gut says, given the size and impact of the soy lobby, it's more likely that soy is a net-negative and this is being suppressed, than the converse.
kerlynb from Philippines, Southeast Asia, Earth ^_^ on November 04, 2011:
I've always been a fan of tofu so I really appreciate this hub. I like tofu for its soy proteins, makes me able to substitute meat with something healthy and filling. Wow, there are possibly bad effects of eating tofu? Thanks for mentioning. So I need to eat tofu in moderation.
Lily Rose from A Coast on November 04, 2011:
This topic is close to my heart, as I've been unable to determine, since having breast cancer, whether or not I should eat soy products. My Oncologist, too, is unsure - can you blame her though given what you explained above?? It can help prevent breast cancer while at the same time it can cause it!
I take Femara (Letrozole) and my cancer was estrogen fueled, so my gut tells me that I'm probably better off just staying away from it. I'm okay with that because I'm not a huge fan of tofu or soybeans, but there are several foods that I like that are "diet-friendly" that are made with soy and I'm never quite sure if it's okay to eat them.
This is definitely a great topic to write about and a great hub, I just wish there was a more difinitive answer! :-)
Claudia Tello from Mexico on November 04, 2011:
I was going to vote in your survey but the option of "I occasionally eat soy products" wasn't there, that would be my case. For me, the problem with soy products is that they are almost always packaged process food, and I tend to avoid premade food in which I can't control the quality or the amount of ingredients in it (specially undesirable sugar , fat and salt). I occasionally eat tofu and I love dried soy beans as well as edamame.
Simone Haruko Smith from San Francisco on November 04, 2011:
Love this Hub, and love the chart! I just listened to a podcast on the subject, so the whole soy-estrogen issue is fresh in my mind. Your explanation is fabulous!
The way I've heard the 'health/safety' issue framed is that at first the consensus was that soy made a negative impact, then people kept finding positive impacts, and some of the latest studies suggest that it makes no sort of significant impact at all. Will we ever figure the issue out? Meeerrr... someday... but I don't think I'm going to change my habits. Hahaa!
drbj and sherry from south Florida on November 04, 2011:
Fascinating information, livelonger. Thank you for your meticulous research. Voted up.