How Safe is Soy?

By far, soy is the most controversial plant food. You may have heard the following: “If men eat soy they will get man-boobs” or “Soy causes breast cancer.” Do a quick web search and you will find hundreds of pages on the “dangers of soy.” There are over 10,000 peer-reviewed journal articles on soy making it one of the most researched foods. With this much research, one could make a case against soy by highlighting a handful of outlier studies. Dietary recommendations, however, are made based on a comprehensive review of the research. Let’s see what the research has to say on the following questions:

Is eating soy the same as taking estrogen?

Soybeans contain isoflavones, which are classified as phytoestrogens, or plant estrogens. However, unlike the hormone estrogen, isoflavones selectively bind to one type of estrogen receptor. Depending on what type of receptor dominates in a given tissue, isoflavones can have estrogen-like effects in some tissues, anti-estrogen effects in other tissues, or no effects at all. Conclusions about the health effects of soy cannot be made based on how estrogen behaves in the body.

Does soy cause feminization in men? soyfoods3

In two case studies, men consuming extremely high amounts of soy (14-20 servings per day) developed tender, enlarged breast tissue. In contrast, evidence from randomized controlled trials indicates that soyfoods (up to six servings per day) do not affect testosterone or estrogen levels and isoflavone consumption does not affect sperm concentration, count or motility.

Does eating soy increase risk for breast cancer?

Because hormone therapy increases risk of postmenopausal breast cancer, it was thought that women with estrogen sensitive tumors and those at increased risk of breast cancer should not consume soy. However, research indicates that soyfoods do not have harmful effects on breast tissue. In fact, two large studies found that soyfood intake is associated with the improved prognosis of breast cancer patients, including reductions in risk of death and disease recurrence. The position of the American Cancer Society is that breast cancer patients can safely consume up to three servings of soyfoods daily.

Does soy negatively affect thyroid function?

The evidence clearly shows that soyfoods do not adversely affect thyroid function in healthy people. For those with hypothyroidism on medication, changes in soy intake may require small changes in thyroid medication since soy protein affects medication absorption.

Discussions about the safety of soy continue to appear in the scientific and popular media. Research to date indicates that soyfoods can be safely incorporated into the diets of essentially all individuals.

Soy facts:

  • Soyfoods have been consumed in Asia for at least 1,500 years.
  • Soy protein is considered equivalent to animal protein – it is highly digestible and its amino acid pattern closely matches human requirements.
  • Moderate amounts of traditional soy foods can reduce the risk of prostate cancer and can lower LDL cholesterol.
  • Young girls who consume soy have a lower lifetime risk of breast cancer.
  • The calcium in fortified soymilk is absorbed as easily as calcium from cow’s milk.
  • Only about one out of 2,500 American adults is allergic to soy protein.

For more information:

http://www.veganhealth.org/articles/soy

“Isoflavones” and “Safety of Soyfoods” RD Resources for Consumers. Vegetarian Nutrition Dietetic Practice Group http://vegetariannutrition.net

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Carolyn Tampe

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Comment on this post

20 Comments

  1. Mikael on January 28, 2013 at 2:47 pm

    Wow, this is really great info! I hope a lot of people end up reading this important article that cuts through the soy myths out there. Thanks!



  2. Ginger Hultin Ginger Hultin on January 28, 2013 at 4:07 pm

    So many soy-related myths! Thanks for the clarity 🙂



  3. Douglas on January 28, 2013 at 10:12 pm

    Well informed article that addresses the misconceptions about soy consumption. An illuminating piece for all to read.



  4. on January 29, 2013 at 10:10 am

    Soy has been a controversial topic for so long. Its great that you highlighted some of the fallacies with some of the weaker research and highlighted better studies.



  5. Oliver on January 30, 2013 at 8:32 am

    Great article! This is helping me move towards a totally plant-based diet, which is better for me, the animals, and the Earth. Thank you!!



    • Carolyn Tampe on January 30, 2013 at 6:09 pm

      Thank you for the comment. I have met many people following a vegetarian or vegan diet who were avoiding soy unnecessarily. Happy tofu eating!



  6. Carolyn Tampe on January 30, 2013 at 6:29 pm

    Hello Fellow RDs,

    Click on the above link for a FREE webinar on “2010 Dietary Guidelines, MyPlate and Plant-Based Eating” approved for 1 CPE credit through the Commission on Dietetic Registration.



  7. Carolyn Tampe on January 30, 2013 at 6:30 pm

    Apparently the link did not show up. Here it is: http://soynutrition.com/category/resourcestools/

    Click on Continuing Education



  8. Amber O'Neal on January 30, 2013 at 6:56 pm

    Really informative article that I plan to share. I get asked about soy consumption ALL the time!



  9. Riley on January 30, 2013 at 7:13 pm

    This is good stuff, thanks. What is the best tofu to buy?



  10. queenfluff on January 30, 2013 at 7:39 pm

    Thanks for this article! I keep having someone tell me that the reason a womens periods may be bad is because eating too much leads to estrogen dominance. I don’t think that makes sense. Plant estrogen isn’t the same as human estrogen.



  11. beautifulife on January 30, 2013 at 8:26 pm

    Great information. Unfortunate that the issue of GMO soy and non GMO soy wasn’t brought up. >90% of the soy Americans consume is GMO soy, making most of the soy available dangerous and harmful. The Asian population has been consuming non GMO soy for hundreds of years and have one of the lowest incidences of breast cancer. Probably also related to healthy exercise and lifestyle differences, but largely in part because of the quality of food.

    Next time you think about consuming soy, make sure you know the source.



  12. Dave Grotto, RD on January 30, 2013 at 8:54 pm

    Brava, Carolyn…Brava!! I’m so proud of you! Thanks for this great primer on the use of soy and health.



  13. Liz on January 31, 2013 at 7:39 am

    I love soy and it is a staple in my plant based diet. Thank you for the reassuring info! I will pass this article on to weary friends.



  14. Clive watson on January 31, 2013 at 11:51 am

    Both of the sources listed are corporations interested in the sale of soy products, where are the MEDICAL journal study results? People keep referencing vegetarian and nutritional magazine sources, who have an obvious bias.



    • Carolyn Tampe on February 3, 2013 at 2:13 pm

      Actually neither of the sources listed have any affiliation with the soy industry. Vegetariannutrition.net is run by a practice group of the Academy of Nutrition and Dietetics (largest group of Registered Dietitians). The fact sheets are evidence-based with citations to journal articles. Veganhealth.org is run by a Registered Dietitian and everything on the site has citations to journal articles published in medical journals.



  15. Matt on February 7, 2013 at 9:33 am

    Obviously, the meat industry fears soy products. We do their work for them when we parrot their bogus claims.
    http://whyveganoutreach.blogspot.com/2013/01/clubs-soy-and-choice-we-face.html



  16. Xhris on February 15, 2013 at 3:06 am

    Great article. Yet I ponder 2 questions.
    Do our bodies fully utilize/digest/absorb properly if NOT fermented soy? Esp “Stink tofu” which is hard for most westerners to eat or smell.

    Also researched so much on soy protein isolate and concentrate as it has become an overused protein source in many so called energy bars and faux meats. Wondering if these types of ingredients are truly indigestible for us and protein never gets absorbed, again, unless fully fermented.

    Thanks!



    • Carolyn Tampe on February 17, 2013 at 3:05 pm

      Thanks for your comment Xhris. Soy protein is actually highly digestible regardless of whether it is fermented or not. According to a ranking system that ranks proteins based on their amino acid pattern and digestibility, it is the most highly rated of all plant proteins. Raw soy beans do have compounds in them that reduce digestibility, but these are deactivated by cooking. All of the commonly consumed forms of soy are cooked.

      Some people who write about soy suggest that fermented soy foods are the most healthy and that isolated soy proteins are the most unhealthy. Fermented soy foods are tempeh, miso, and natto. Actually, for the most part, the evidence does not suggest that fermented soy foods are healthier than traditional non-fermented soy foods (such as tofu and soymilk). And most of the research on soy showing health benefits has been performed on isolated soy protein. Furthermore, only about half of the soy eaten in Asia is fermented and the rest is not. The common belief that in Asia, soy is consumed mostly as fermented foods, is not true.