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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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The humble soybean has come a long way. Today, soy is everywhere and in every possible form—beans, nuts, milk, yogurt, cheese, flour, tofu, tempeh, and “meat” analogs, to name a few. You can eat soy alone, cooked, or combined with other ingredients for a fantastic high-protein, low-fat snack or meal. In fact, one in four Americans eats a soy-containing food at least once a week.

Soy is a powerful plant food, packed with valuable protein, essential fatty acids, numerous vitamins and minerals, and fiber. It also contains phytochemicals such as isoflavones, phytate, saponins, and phytosterols. As one of the most widely researched foods for potential health benefits, soy has been touted as a miracle food that may fight cancer, heart disease, osteoporosis and more. But lately, this innocent bean has become the center of confusion and controversy. Several soy studies have yielded inconsistent results and consumers have been bombarded by mixed messages from the media. So here is the rundown on the science behind soy.

Heart Health
In 1999, the Food and Drug Administration (FDA) concluded that adding soy protein to a diet low in saturated fat and cholesterol could decrease the risk of coronary heart disease (by lowering blood cholesterol levels). The American Dietetic Association (ADA) also released a statement recommending 25 grams of soy protein daily to help reduce the risk of heart disease. But current research has been unimpressive, finding that soy protein only decreases LDL (bad) cholesterol by three percent and does not increase the HDL (good) cholesterol.  The bottom line: Soy’s role in improving cholesterol is small. Even though soy has a relatively modest effect on cholesterol levels, it still can be included as part of a heart-healthy diet.

Breast Cancer
For consumers, the connection between soy and breast cancer may be the most confusing. After over 15 years of research on this topic, we don’t have any clear-cut answers. In theory, the plant estrogens in soy foods act as anti-estrogens. This means they may block natural estrogen from reaching the cells’ estrogen receptors. Therefore, soy is probably beneficial when the breasts are developing during childhood, making them less vulnerable to cancer. Later in life, when pre-menopausal women experience high levels of natural estrogen, the estrogens in soy may compete with natural estrogen resulting in positive benefits.

Post-menopause women, however, have low levels of natural estrogen. Adding plant estrogens at this time may increase the risk of breast cancer. Soy isoflavones may enhance tumor growth in women who have (or have had) estrogen-dependent cancers (like some breast cancers). The bottom line: Studies have not reliably demonstrated an increased or decreased risk of breast cancer among women eating soy. The American Institute for Cancer Research (AICR) states that soy consumption early in life may help protect against breast cancer later in life. The American Cancer Society suggests that those at risk for breast cancer should not consume soy isoflavones.
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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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