Nutrition Articles

The Science Behind Soy

Confused about Soy? You're Not Alone.

By Becky Hand, Licensed & Registered Dietitian         
Page 2 of 3

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.
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About The Author

Becky Hand Becky Hand
Becky is a registered and licensed dietitian with almost 20 years of experience. A certified health coach through the Cooper Institute with a master's degree in health education, she makes nutrition principles practical, easy-to-apply and fun. See all of Becky's articles.

Member Comments

  • Yay, Becky! Count on you to present the scientific evidence instead of the mainstream headlines. Thank you. - 1/11/2016 12:17:58 PM
  • I have been eating and cooking with soy for almost 3 years and have seen quite a bit of health improvements. - 7/13/2014 8:31:23 PM
    It's obvious that all human bio-systems are not created equal. We have different blood types and genetic compositions. What is good for one may not be so for another. For instance, some of us are actually allergic to Benedryl - a med that is commonly prescribed to counteract many allergic reactions. In addition, at 58, I have come to realize that my own system continually changes from decade to decade, requiring modification of diet in order to function normally. Most of what we know about nutrition and exercise - good or bad -can be individually applied based on what our own bodies tell us. Minimizing stress and NOT trusting our government's involvement in our diets is probably a good start.... - 1/5/2014 11:45:52 AM
  • I am at a point where I question anything the government agencies tell us. FDA - a lot of what they tell us is hype, something to keep us addicted to sugars, grains, etc. I will do my research and believe what I learn. It is time we as consumers let the government and businesses know we do not want everything "they" think is good for us. It is my money and I am now in the business of eating healthy - organic, non-GMO, non-processed. - 11/24/2013 3:40:03 PM
  • The majority of the soy grown in the USA is genetically-modif
    ied and for that reason alone I will not eat it. As someone who teaches genetics at the college-level I am greatly concerned as NONE of the GM foods have been adequately tested (despite what you have heard in the media). Independent studies have found serious links to environmental damage and health problems. - 10/11/2013 7:13:06 PM
  • Before believing anything that is written on any website you need to do your own research. Evidence based practice shows soy to be causing children to have menarchy earlier than average and women to have harder times to get pregnant and going to term. I love Sparkpeople but please make sure to do your own research as well and to decide yourself what is true or not. - 10/11/2013 5:22:07 PM
  • I wish you would've included something on soy's effect on acne! - 10/11/2013 4:20:02 PM
  • I only have soy in limited amounts because I take thyroid meds, but I find that it helps me feel better when I have PMS symptoms, so I'll only eat/drink soy-based foods around that time. - 10/11/2013 11:54:49 AM
  • Never really new that much about soy. Thanks - 9/2/2013 1:04:21 PM
  • 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
  • WoW! Looks like soy does everything but cure back-aches and the common cold...hmmmmm. - 5/14/2013 1:09:15 PM
    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
  • 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
  • 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
    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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