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Soy and Women’s Health: The Truth About Soy Benefits and Safety

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I have received hundreds of questions about soy safety. They include:

I’m pregnant and vegetarian and am trying to get enough protein in my diet. Is soy safe for me and my baby? I’ve heard it can cause hormonal problems and interfere with my nutrient absorption.

I’ve heard soy can cause thyroid problems.

I’m approaching menopause and am having horrible hot flashes. My doctor told me to drink soymilk butI’m just not sure that it’s safe.

My mom had breast cancer and I’ve heard that eating soy could increase my risk…

In the past decade, vegetarianism, including veganism, has become in vogue, and with this, soy has received a lot of positive – and negative – press. Touted health benefits include cholesterol reduction, the prevention of osteoporosis, heart disease, and cancer, and the prevention and treatment of menopausal symptoms. Yet critics have called it a “poison,” with the nutrition author Sally Fallon questioning whether soy is “the next asbestos.”

In a hurry? For my bottom line on soy, you can skip to the end of this article.

Bit of a health geek? Read on for the whole soy story…

 

Background: My Own Soy Odyssey

My first intentional encounters with soy were as a 15-year old vegetarian in 1981. I knew I needed protein and back then, the road to healthy eating wasn’t as clear as it is now and info was not as readily accessible. Tofu was an obvious choice – it was inexpensive, easily available, and packed a lotta’ protein in a small amount. And it didn’t require me to soak it and pressure cook it the way beans did.

Frankly, I pretty much hated tofu from the get-go, in just about all forms except the firm style, heavily seasoned with tamari and garlic. I’m still not a huge soy fan, though I pushed myself to eat it through my four vegetarian pregnancies to get enough protein for my growing babies. I don’t think it tastes that great, and it’s not the easiest food to digest. So I eat traditional forms, on rare occasion. I’ve always been a bigger fan of the other, and in my opinion, more flavorful beans such as black beans, garbanzos, and kidney beans, as well as nuts and seeds, for my protein.

As a mom raising 4 vegetarian kids, and through teaching thousands of patients how to eat healthy, plant-based diets over the past 25 years, including thousands of pregnant women, I’ve done quite a bit of research on the health benefits – and risks — of soy.

So what’s the deal? Is soy healthy? Dangerous? Somewhere in between? Many of you have written me with questions and concerns. I found myself thinking: “Soy veh! I’d better write an article!” This piece will hopefully dispel your soy-confusion and give you some practical advice on whether and how to eat soy, safely.

Soy in the Diet
Miso Vats for fermentation

Miso Vats for fermentation

Soy has been a staple in the traditional Japanese diet for centuries. Okinawans, who consume more soy in their diets than any other people in the world, 1-2 portions daily, have more centenarians (folks alive over 100 years old) than any other culture on the planet. They also suffer lower rates of heart disease, osteoporosis, dementia, and breast cancer than Americans.

However, soy is only a small part of an overall healthy lifestyle. Okinawans eat all foods in moderation, following the Hara Hachi Bu rule of eating only to 80% full, and a low caloric intake diet is known to promote longevity. They eat a predominantly plant-based diet, with meats and traditional soy products as a complement, not an “entrée.”

They also exercise regularly, have psychospiritual practices that minimize stress, and have other lifestyle habits that promote health and longevity. So yes, traditional soy foods are a part of the equation of their healthy long lives, but only a small part.

Soy products can be divided into 3 main categories:

1. Traditional soy foods: Traditional forms of soy include tempeh, natto, miso, and tamari – all of which are fermented – tofu, and soymilk (yes, soy milk is a traditional food). Traditional daily soy intake appears to range from 25-40 g, roughly equivalent to 100-160 mg of isoflavones, the natural plant chemicals in soy that are thought to be beneficial to our health. In the US these foods are generally made from organic, non-GMO (genetically modified organism) soybeans.

2. “Frankensoy”: These are soy alternatives to common meat and dairy products, for example, tofu hot dogs, soy cheese, sweet soy milk in all sorts of flavors, soy yogurt, soy ice cream, soy bacon, soy sausage links, and soy burgers. Even when made from organic, non-GMO beans, these are generally highly processed soy junk foods and not part of a healthy diet. Soy protein isolates, often used to boost nutrition in protein shakes, and in menopausal supplements, are also, generally, forms of Frankensoy.

3. Processed, GMO, junk filler soy: Approximately 90% of the soy produced in the US is genetically modified to be resistant to herbicides, namely, Roundup, produced by Monsanto. Since soy is one of the most common ingredients in mainstream foods, this is a big deal!

There are many concerns about consuming genetically modified products. The two major health concerns about GMO soy are: 1) higher than legally allowable levels of pesticide residue remain on the crop, which we eventually ingest, and 2) the health effects of eating genetically modified products is unknown – it has even been raised as a health concern by Monsanto. GMO soybeans are nutritionally inferior to natural soybeans, and contain lower levels of the isoflavones that are the primary health-promoting constituent.

Soy has infiltrated the American diet as an inexpensive meat and dairy alternative, and a nearly ubiquitous cheap commercial food filler, protein fortifier, and oil. My 18-year old daughter, raised vegetarian eating whole, natural foods, with a modest amount of soy on occasion, recently bemoaned that practically all of the foods in her college cafeteria list soy as an ingredient. She’s right – it’s in practically everything.

The good news is that most traditional, organic soy products in the US are made from non-GMO soybeans. The Non-GMO Project is a non-profit organization “committed to preserving and building sources of non-GMO products, educating consumers, and providing verified non-GMO choices.” You can find a list of good quality soy products on their website. Avoid all GMO soy products. 

Are There Health Benefits to Eating Soy?

The answer to this, based on extensive review of the scientific and popular literature, is a resounding YES, there are. Here’s a breakdown of some of the major benefits of soy for women:

Breast Cancer Prevention

Studies have shown that Asian women who have consumed traditional soy products since childhood or adolescence, indeed, have significantly lower rates of breast cancer. Some studies on the breast cancer preventing effects of soy have been conflicting. Overall, however, large reviews of studies called meta-analyses show that soy consumption either has a beneficial impact on breast cancer development, or no impact, but it does not pose a risk.

The breast cancer protective effects of soy are primarily attributed to a group of chemical constituents in soybeans known as isoflavones, which in turn belong to a class of chemicals known as phytoestrogens. They are strikingly similar in structure to the estrogens produced by our bodies, but are weaker than human estrogen, competitively bind with estrogen receptor sites in breast tissue, preventing the stronger “endogenous” estrogen from binding – thus possibly blocking them from causing cancerous changes in the tissue.

Treatment and Prevention of Menopausal Symptoms

Studies on the benefits of soy isoflavones on various menopausal related symptoms have shown generally favorable improvements in perceived vasomotor symptoms, particularly hot flashes. Studies on cognitive function have been mixed; some have shown improvement, however, a single study of older women living in Japan, eating a traditional Japanese diet, had worse cognitive function than women eating a western diet; Hawaiian, though conclusive information cannot be gleaned from this singular study.

Prevention of Osteoporosis

Several smaller, and one large study have shown that the soy isoflavones, especially genestein, reduce bone loss, though no studies have been done over a long enough time to look at fracture prevention. Approximately 3 cups of soymilk, 6 oz. of tofu or tempeh, or 3 oz. dry roasted soybeans (edamame) would provide roughly the amount of soy isoflavones used in the studies.

Cholesterol Reduction and Heart Disease Prevention

Soy makes a reliable positive contribution to a heart healthy diet, especially through cholesterol lowering effects. The recommended amount is 25 grams/day of soy. The FDA approves this health claim. Eating soy may also help lower high blood pressure. In general, a plant-based diet, not just soy, can have these benefits, but soy is an easy addition.

Are There Health Risks to Eating Soy?

A number of concerns have been raised in the popular media about the safety of soy, especially about fertility, thyroid function, and nutrient absorption. Any health risks associated with eating traditional soy foods as a modest part of the diet appear extremely minimal. Here’s a quick review:

Breast Cancer Risk: Eating soy in normal dietary amounts does not appear to increase the risk of breast cancer in any populations, in any study. More likely than not, it has some protective effects. But if it worries you, don’t eat it. Remember, many plant-based foods contain similar phytoestrogens.

Fertility: There has been no evidence of decreased fertility in women or men consuming traditional dietary amounts of soy. No feminizing effects have been seen in men consuming normal amounts of soy foods.

Soy and Thyroid Problems: A review of the literature demonstrates that women with normal thyroid function and normal dietary iodine intakes are not at risk for developing thyroid problems. Even eaten up to 3 times/week in pregnancy, it does not affect thyroid function in otherwise healthy women. Make sure you are getting enough iodine in your diet through iodized salt, seaweeds, or your vitamin supplement. If you do have thyroid problems, soy may not be for you. If you are on thyroid medication, your doctor may need to adjust the dose if you supplement with soy foods, as soy can interfere with the medication’s activity.

Soy allergy: Soy is a common food allergen. If you are allergic – or even sensitive (you have digestive or other symptoms after you eat it) — avoid it, or work with your primacy doctor to see if an elimination diet with later re-introduction is a possibility. Organic, non-GMO soy may be less allergenic.

Interference with Nutrient Absorption: Phytic acid is found within the hulls of nuts, seeds, grains, and beans, including soy. It is an indigestible form of phosphorous that can bind to and interfere with mineral absorption. Phytates are reduced somewhat by cooking, and when consumed in normal dietary amounts in those with an adequate nutritional status, should pose no problems with nutrient absorption. Soy has not been shown to interfere with normal growth. Lactobacilli and other organisms in probiotics contain phytase, which help to break down phytates in the intestine.

Is Soy a Necessary Part of a Vegetarian or Vegan Diet?

Soy is absolutely not an essential ingredient in your diet.

If you feel the jury is out on soy safety, feel free to pass the plate. 3113There are many other excellent vegetarian sources of protein and calcium, particularly other beans and legumes, nuts and seeds, and green leafy vegetables that will adequately meet your nutritional needs. The hormonally beneficial plant compounds found in soy are also found in a variety of beans and leafy green vegetables – eat a wide array of these daily for optimal health.

SUMMARY: Safe Soy Consumption in a Nutshell
  • Eat only organic, non-GMO, traditional soy foods, particularly fermented forms (soy milk may be an exception as a “medical food” for symptom control during the perimenopause), as a small part of an overall healthy, plant-based diet.
  • Eat soy, in moderation, as a small part of an overall healthy, plant-based diet. Soy should only be a complement to your diet, not a mainstay. I generally recommend a maximum of 2-3 servings/week. Emphasize other high quality protein sources for healthy variety in your diet.
  • Completely avoid “Frankensoy” products.
  • If you have thyroid problems, or are on thyroid replacement medication, work with your doctor to monitor your levels if you eat soy regularly (> 1 x/week).
  • Make sure to get adequate dietary or supplemental iodine if you eat soy regularly.

 

Have questions about soy and your kids? Please see my upcoming post, Kids and Soy: Should They Eat It? Have questions about the article or soy? Post ‘em below!

 

References

Atkinson, C. et al. Lignan and isoflavone excretion in relation to uterine fibroids: acase-control study of young to middle-aged women in the United States. Am J Clin Nutr. 2006;84:587–93.

Bruce, B. et al. Isoflavone supplements do not affect thyroid function in iodine-replete postmenopausal women. J Med Food. 2003 Winter; 6(4): 309-16.

Famularo G, et al. Probiotic lactobacilli: an innovative tool to correct the malabsorption syndrome of vegetarians? Med. Hypotheses 2005 65 (6): 1132–5.

Kritz-Silverstein, D. et al. Isoflavones and cognitive function in older women: the soy and postmenopausal heath in aging (SOPHIA) study. Menopause. 2003 May-Jun; 10(3): 196-202.

Jing L. et al. Effects of dietary soy intake on maternal thyroid functions and serum anti-thyroperoxidase antibody level during early pregnancy. J Med Food. 2011; 14(5): 543-50.

Marini H, et al. Effects of the phytoestrogen genistein on bone metabolism in osteopenic postmenopausal women: a randomized trial. Annals of Internal Medicine. 2007 Jun. 146(12): 839-47.

Messina, M. Soybean isoflaone exposure does not have feminizing effects on men: a critical examination of the clinical evidence. Fertility and Sterility. 2010; 93 (7): 2095-2102.

Messina, M. et al. Estimated Asian adult soy protein and isoflavone intakes. Nutr Cancer. 2006; 55(1): 1-12.

Messina, M. and G. Redmond. Effects of soy protein and soybean isoflavones on thyroid function in healthy adults and hypothyroid patients: a review of the relevant literature. Thyroid. 2006 Mar; 16(3): 249-58. 

Messina M et al. Skeletal benefits of soy isoflavones: A review of the clinical trial and epidemiologic data. Current Opinion in Clinical Nutrition and Metabolic Care. 2004, Nov. 7(6):649-58.

Okinawa Centarian Study http://www.okicent.org/study.html

Setchell, K. Assessing risks and benefits of genistein and soy. Environmental Health Perspective. 2006 Jun; 114(6): 332-333

Upmalis, DH. Et al. Vasomotor symptom relief by soy isoflavone extract tablets in postmenopausal women: a multicenter, double-blind randomized, placebo-ctronolled study. Menopause. 2000 Jul-Aug; 7(4): 236-42.

Washburn S, et al. Effect of soy protein supplementation on serum lipoproteins, blood pressure, and menopausal symptom in perimenopausal women. Menopause. 1999 Spring; 6(1): 7-13.

 

 

 

 

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Comments

  1. I’ve learned that it also depends on your hormonal composition – that if soy has an estrogen-mimicking effect, and you need more estrogen, by all means eat good versions of it – if not, be sparing. If you have a thyroid issue, it depends if it’s hypo or hyper thyroidism. This would make sense to me, as everyone should be eating according to their own composition, though I’m not an expert on it, I just did one training. I’d love to know more of what you think in accordance with this line of reasoning. I see what you’re saying that overwhelmingly we have been scared off of soy in even traditional forms and that generally it should be ok, especially in moderation. Thanks!

  2. thank you for this wonderful information. what are you thoughts on the effects of traditional soy foods for women with endometriosis?

    blessings.

  3. Thanks so much for this. This is very helpful information.

  4. Thanks for this really helpful info, Aviva. What do you think of “soy compound”? The packet says it’s 72% soy, maltodextrin, seaweed, vegetable gum (415), flavour (not stated what, exactly). Made in Australia. My husband is lactose intolerant, and I’m trying to find an ingredient to replace evaporated milk, cream, etc to use in cooking. He can have lactose-free milk, but all other milk products upset his digestive system. Looking forward to your reply.

  5. One of the more balanced viewpoints I’ve read on the subject, thank you.

    • I couldn’t agree more. Thank you for this both evidence-based and holistic discussion of soy. I appreciate your balanced perspective.

  6. P.S. My husband also doesn’t like tofu AT ALL, but can handle soy milk and soy icecream.

  7. I am looking forward to your article about kids and soy. I especially wonder about soy formula for babies? I nursed exclusively for two months but then had surgery and had to start giving some formula. I am working on rebuilding my supply as I know that breastmilk is best but right now my five month old daughter gets about half organic soy formula (Baby’s Only) and half breastmilk. I initially gave her a dairy formula but she experienced a rash each time she drank it. Is soy dangerous for babies to consume regularly? Does it matter that the formula is organic and non-GMO?

  8. Thanks for writing this article, Aviva. I am curious, though, about the hormonal interactions. My understanding has been that the endocrine active phyto constituents in soy may be helpful to menopausal women, or others not producing adequate estrogens, but that it would compete with estradiol for receptor sites, and thus inhibit normal, healthy hormonal activity in young women, those wishing to conceive, etc. I understand your statements were in regard to eating a healthy amount, and that moderation is a factor, but is it not true that it can interfere with fertility and pubescent development, just as it may support the natural decrease in estradiol through the menopausal transition?

  9. I’ve been led to believe that the current rise in thyroid dysfunction in this country is directly related to the increase in soy additives in our processed foods. Has there been any reputable studies to this effect, or do you have an opinion about it?

  10. Aviva, what is your opinion on the idea that there are multiple estrogen receptors and that, rather than competitive inhibition by soy isoflavones, compounds such as genistein (an isoflavone from soy) are actually much stronger agonists of estrogen-receptor-beta than mammalian estrogens are? ER-beta seems to be strongly anti-proliferative, anti-cancer: it is as if phytoestrogens are a naturally-occurring counterbalance to mammalian estrogens. This explains a lot: in menopause, weak ER-alpha activity helps buffer the drop in endogenous estrogens, but the strong anti-proliferative ER-beta activity remains, hence cancer prevention.
    McCarty, Mark Frederick. “Isoflavones made simple-genistein’s agonist activity for the beta-type estrogen receptor mediates their health benefits.” Medical hypotheses 66.6 (2006): 1093.
    http://europepmc.org/abstract/MED/16513288

    • Hi Guido, Well, it’s not a theory that there are multiple estrogen receptors; this is a well established reality. As to whether soy is a stronger agonist of estrogen receptors than endogenous estrogen, this is probably dependent on the type of estrogen we are talking about — I highly doubt it is stronger than estradiol, but it is possibly more potent than estriol, which is rather weak relatively. So in menopause it may very well be the case the genistein and other isoflavones are stronger; but this is unlikely in younger women who are non-pregnant, especially given the fact that we know that soy isoflavones do not lead to endometrial hyperplasia, which is sort of a hallmark of estrogen activity. Thanks for the lead on the article. I LOVE to read and keep up with the literature. And I agree — nature has the most ingenious and marvelous ways of keeping us healthy when we stay in harmony with natural rhythms and lifestyle — especially our foods, and using herbs as foods — something I know we are both fond of! :)

  11. So one of the benefits of soy is breast cancer prevention, and one of the detriments is increased breast cancer risk. How, exactly, does that work? And if it’s the fermentation of soy that makes it safer for us to eat, and non-fermented soy should be avoided, why is soy milk OK when other forms of non-fermented soy aren’t?

  12. Hi,

    I breastfeed my baby but I can not express much milk. I do not want to feed her cow milk based formulas as I do not agree with giving her other animal milk. You can get soya based baby formulas, as a top up to her breastfed an solid food diet when i leave her if needed , do you see any negatives?

    • hi kristy,
      i do not know how old your baby is, but the best thing is just to breast feed her directly unless you have a medical or work reason that you need to pump. but yes, soy milk formulas are an option for babies when needed. overall, the research does not point to anything major hazards or soy formula, but if it is not organic, then there are concerns about contamination from pestidices, and many of us are concerned about GMO products. Be well.

  13. Bindarella says:

    Is the post on ‘Kids and Soy: Should They Eat It?’ out?

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