Nutrition Articles

The Science Behind Soy

Confused about Soy? You're Not Alone.

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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 Academy of Nutrition and Dietetics (formerly the American Dietetic Association) 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. 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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