Nutrition Articles

The Science Behind Soy

Confused about Soy? You're Not Alone.

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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.

Thyroid Function
The results of over 10 clinical trials demonstrate that soy foods and soy isoflavones have little or no effect on thryoid function in healthy adults. However, it has been discovered that individuals taking synthetic thyroid hormone medication may require about a 25% higher dosage of medication if they consume soy foods. Researchers have suggested that the increase in this medication requirement is due to an increase in the medication being excreted in the stool and/or a reduction in medication absorption—not due to a direct effect on the function of the thyroid. If you consume soy products and use thyroid medication, talk to your doctor for appropriate medical care. The bottom line: Soy doesn't appear to damage the thyroid in healthy people or people with thyroid problems. However, people on thyroid medication should talk to their doctors about soy consumption.

The Joy of Eating Soy
Based on the evidence to date, a variety of soy foods, whether fermented or nonfermented, can be included in the daily diet. Health claims stating that nonfermented soy foods contain toxins that block enzyme activity have not been documented by any scientific research. Here are some suggestions for individuals who choose to include soy in their diets.
  • Food is always better than pills. So in this case, eating soy foods is typically safer and more beneficial than soy supplements or pills.
  • For people who want to eat soy products, up to one to two servings per day is appropriate. Examples of a single serving include:
    • 1 cup soymilk
    • 1/2 cup tofu
    • 1/2 cup soy protein (tempeh)
    • 1/2 cup edamame
    • 1/2 cup roasted soy nuts
       
  • For people concerned about GMO (genetically modified organisms) or pesticide exposure, organic soy products are non-GMO and free of pesticides.
  • Be wary of ads and too-good-to-be-true claims for soy-based pills, powders and supplements.
  • For those with a high risk (or history) of estrogen-dependent cancer, soy may be the wrong food. Discuss possible soy consumption with your health care provider, along with medical history, risk factors and treatment options.
While it is not a miracle food, moderate amounts of soy can be part of a healthy diet. As the research on soy continues, it is best, like many things in life, to exercise moderation and caution.
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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

  • 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
  • SWISSWEGIAN
    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
  • RACEWELLWON
    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
  • 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
  • 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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