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The Science Behind Soy

Confused about Soy? You're Not Alone.

-- By Becky Hand, Licensed & Registered Dietitian
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Prostate Cancer
Japanese men have lower rates of prostate cancer than men in the United States, and some experts contribute that to the Japanese diet, which is high in soy foods. The results of a few animal studies showed promise in this area. However, two small studies on humans (men) yielded controversial results. Soy isoflavones appeared to lower and improve the PSA (prostate-specific antigen) score for some men. For others, PSA level increased, but at a slower rate. And for certain men, the isoflavones worsened the prostate cancer condition. The bottom line: There are not enough human studies to say whether the isoflavones in soy affect prostate cancer for better or for worse.

Menopausal Symptoms
Does soy relieve hot flashes, night sweats and other menopausal symptoms? Could soy isoflavones be the reason that Japanese women have a lower rate of hot flashes? Current research does not indicate this and study results have been very inconsistent. Roughly 60 percent of trials showed only modest reductions in hot flashes, while the other 40 percent showed no improvements. The bottom line: The claims that soy helps with menopausal symptoms have been blown way out of proportion. The evidence just does not show much benefit.

Bone Health
It is still too early to conclude whether or not soy helps to build bones. There are currently a few long-term studies investigating the area of soy and bone health. Contrary to popular belief, Japanese women experience as much (if not more) osteoporosis as Caucasian women in the United States. They do suffer fewer bone fractures, but this may be due to genetics or the shape of their bones. The bottom line: Although it will be a few years before the long-term studies conclude, it does look like soy may benefit the bones. Although soy probably does NOT reverse bone loss, it may help prevent bone loss and increase bone density.

Brain Power
Does soy improve ones cognitive functioning? Very little research has been conducted in this area. But one small, preliminary study on older adults showed that soy isoflavones did improve cognitive functioning. The bottom line: More investigation is needed in this area.

Weight Control
Although weight management is of great interest to many, very few studies have been conducted in this area. The bottom line: Currently, no studies to indicate that soy protein will enhance weight loss.

Infant Formula
If you search the Internet for “infant soy formula” you’ll find countless reported concerns that center on hormone-related changes observed in studies where animals consumed a high amount of isoflavones. There appears to be a lot of hype without scientific basis. Currently the world’s largest soy formula-feeding study is being conducted in the United States, releasing information as it becomes available. So far, it appears that healthy babies on soy formula grow as healthy children should grow and have normal brain functioning and development. The bottom line: While we wait for the final results of this study, parents should discuss breastfeeding and formula feeding with their infant’s health care provider.
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About The Author

Becky Hand Becky Hand
Becky is a registered and licensed dietitian with almost 20 years of experience. Through her company, An Ounce of Prevention, she makes nutrition principles practical, easy to apply and fun. See all of Becky's articles.

Member Comments

  • CALLMECARRIE
    I like articles like this that give even, thoughtful coverage of available studies. There is no blanket endorsement or rejection of soy here. Thanks Dietician Becky. - 5/21/2013 8:39:22 AM
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  • 6BALLMAN
    WoW! Looks like soy does everything but cure back-aches and the common cold...hmmmmm. - 5/14/2013 1:09:15 PM
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  • RACINGTOLOSE2
    This article really helped me - Soy has often been a difficult subject for me. All issues clear after reading. Being older and in remission from Breast Cancer and on thyroid medications. Soy is not an option . - 12/4/2012 10:52:24 AM
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  • SILVERANGEL6
    No-one has mentioned the way soy is extracted from the bean(?). The traditional way of extracting it means it's an extremely beneficial food for us. But as usual, ,Western manufacturers have taken this & found an easier and cheaper way to do this, thus making it a definitely bad food for us. There's lots of evidence I have read on the Net, which explains the different methods of processing it. Result? It's in almost all packaged foods, try finding stuff without it in there, look at the ingredients list. It's just like sugar. All the big corporations want is our money.
    I won't buy anything with soy in it. I gave up sugar, and soy. Now I feel good again, which I didn't before. I gave up sugar in Sept 2010, gave up soy about 5 - 6 months later.
    Glad I did. I suggest you all do you own research, then you can make up your own mind. I agree with the person who said where was the reference to the research?
    Good try, but not good enough.

    Silver Angel

    Spread the Love

    - 12/4/2011 1:06:52 AM
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  • FOXSTAR10
    Soy saved my life. I was born lactos intolerant. My mother could not breast feed me and I could not tolerate the regular fomula. It took the doctors about 6 months to figure out what was wrong with me. Once I was started on the soy formula I was fine. To this day I cannot tolerate milk. Butter, cheese and ice cream in small quanties are ok. I think I can tolerate them because of the processing.

    Everyone must make their own choice to use or not to use soy. I do. - 11/25/2011 8:54:56 PM
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  • FLUFF2BUFF
    Really...the millions of asians consuming soy products have very little problems and happen to be some of the healthiest people in the world. I have eaten soy my whole life and it wasn't until I moved out on my own and started eating a more westernized diet that I started gaining all this weight. I'm Korean, btw, and we eat a heck of alot more than 2 tbs of soy products. Just saying, it might not be for everyone but shouldn't blanketed as a bad food. - 11/25/2011 4:56:07 PM
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  • CZECHENS
    Although I had a hysterectomy over 20 years ago, as little as a cup of soy milk will give me breast pain, "menstrual" cramps, the whole deal--just like the bad old days. I avoid soy like the plague and would never ever give it to a child--male or female. - 11/25/2011 9:47:14 AM
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  • SUNNYARIZONA
    I avoid SOY products as MUCH as possible....Soy should NOT be eaten like it is here in America. The countries where it originates from....the people do NOT consume it like we do. One BIG side effect of SOY, is HYPOTHYROID....Th
    at is such a HUGE problem for so many today, plus KIDS....could there be a connection between the injestiong of soy and all sorts of problems kids have today. Scarry. - 11/23/2011 4:42:02 PM
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  • THEMANDIKAT
    In no way do I want to criticize this article.. But I'd REALLY like for there to be a bibliography at the end of articles like this.. Maybe a few peer reviewed journals? This is a current topic, and I'm sure there's new research being conducted on soy every day.. It's a cheap food source that can be made in bulk. The science of foods like soy and corn is always in a state of flux.. I'd love to see where you're getting your information (and who is funding the studies, to ensure impartiality!) - 11/23/2011 10:31:35 AM
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  • HXCJOY40
    Maybe you should read this http://articles.m
    ercola.com/si
    tes/articles/
    archive/2010/
    09/18/soy-can
    -damage-your-
    health.aspx?e
    _cid=20111123_DNL_HTL_soy - 11/23/2011 10:07:18 AM
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  • CRITICALMASS
    GINAV2. Did you actually read the article? It has a whole paragraph on Thyroid function and soy. - 11/23/2011 8:37:12 AM
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  • GINAV2
    I'm very disappointed that this article doesn't mention the thyroid effects on soy. On top of its weak estrogenic activity, soy is also goitrogenic (meaning it contributes to hypothyroidism and goiter formation). IMHO, the nutrition from soy isn't worth the possible risks. I'll take lean meats and veggies over this legume any day! - 11/23/2011 7:16:03 AM
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  • ZMILENA
    I use soy in many forms but I am a bit scared of it. I was wondering if soy use can increase body hair growth in women, since it decreases the estrogen. This is one of my biggest concern.
    As for the GMO please, please you all make sure you eat GMO-FREE products! - 11/23/2011 4:48:59 AM
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  • SUNNYARIZONA
    I recently received a very thorough good pamphlet on Soy, and why we should AVOID IT....
    In the orient, they do NOT consume Soy like Americans. At most maybe 2 tbsps. a day, that is all....Soy is NOT a food we should be eating like we do....BAD stuff...I avoid it myself. - 8/20/2011 9:35:54 PM
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  • GUS4ME
    Until now I had been clueless on Soy anything. Thank you for this article. - 8/18/2011 12:48:10 PM
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