Soy: Superstar Health Food or Really Bad Idea?

Thursday Mar 12 | BY |
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edamame, boiled green soy beans, japanese food

Studies have shown mixed results on soy—should we avoid it or not?

In a 2011 survey, about 81 percent of consumers rated soy as healthy. About a quarter said it was beneficial for heart health and a fifth mentioned it was a good source of protein.

Many also stated it was low in fat, helpful for menopausal women, and good for those looking to reduce their dietary cholesterol.

Those reading this blog may vehemently disagree.

Soy, good for you? It’s all a marketing ruse, you might say. Soy is a hormone disruptor, with ties to thyroid disease, cancer, and digestive issues.

It’s true that industry players looking for profits pulled the “everyone should eat more soy” bandwagon for years. But then came the studies suggesting soy wasn’t all it was cracked up to be, and too much could cause more health harms than benefits.

When the dust clears, we’ll likely see that soy, like most foods, has a good and bad side. The key is to know when and how it may be beneficial—or harmful—for you.

A Brief History of Soy in the U.S.

The U.S. began importing soybeans in the early 1900s, and soon after, found they were a good source of protein and oil. Farmers also discovered soy could help replenish soils with nitrogen and minerals, making it a good choice for “rotation” planting.

In the 1920s, scientists used it to develop meat substitutes, and by the 1940s industry experts were using it to make plastics for automobiles. Soybean meal (the waste product after soybean oil is made) became the preferred choice of protein for animal foods in the 1950s, because it was high in protein and affordable. Farmers were soon feeding it to chickens, turkeys, cattle, and hogs. Soybean meal remains a staple in animal feed today.

In the 1990s, genetically modified soy took hold in the U.S., and by 2004, 85 percent of soy crops were GMO crops (bred to resist the Roundup pesticide). Though these crops reduce soil erosion and increase yield per plant, they may also increase risk of potential health problems and spawn the growth of “superweeds” that can resist pesticides.

Today, there are more than 72 million soybean acres grown in this country.

How Did Soy Become So Popular?

Starting in the late 1990s and moving through the first decade of the new century, soy enjoyed a gradual rise in popularity as newspapers, magazines, and health writers proclaimed its many health benefits.

In 1999, the FDA approved the health claim that soy protein lowers cholesterol, giving the food’s healthy image a powerful boost. Similar claims were soon approved in other countries, including Korea, Brazil, the United Kingdom, and more.

Scientists jumped on the fact that people in places like Japan, China, and Singapore had lower rates of breast cancer, prostate cancer, heart disease, and osteoporosis than people in the West. Since these populations all consumed soy foods, perhaps that was the key?

A number of studies during this time seemed to prove that soy was something all health-minded citizens should be adding to their daily diets:

  • Cancer: For one, soy-containing diets seemed to have a positive effect on cancer rates. In 2005, for instance, an animal study showed that rats that consumed soy protein had lower incidences of breast and colon cancer. An earlier 2000 study found similar results—diets rich in soy reduced breast tumors by 20 percent. In a 2000 study of Japanese people, those who ate more soy had lower rates of stomach and colorectal cancer. Soy provides a concentrated source of isoflavones—compounds with a weak estrogenic activity (they can act like estrogen, the female hormone, in the body) that could inhibit the function of estrogen enough to potentially reduce the risk of estrogen-driven cancers like those of the breast and prostate. Some laboratory studies also showed these isoflavones to inhibit the growth of cancer cells.
  • Heart Disease: People who consumed more soy in their diets seemed to have a lower risk of heart disease. In a 2000 study, for instance, researchers analyzed soy intake and mortality from heart disease in Japan. They found those who ate more soy had a lower risk of death from heart disease. A 2003 study of Chinese women found similar results—those who reported consuming more soy foods had a lower risk of coronary heart disease and a lower risk of heart attack. In a 2001 study, researchers found that soy protein helped control LDL “bad” cholesterol by activating LDL receptors in the liver, resulting in a lower level of cholesterol in the blood. An earlier 1995 meta-analysis of 38 human trials showed that eating about 50 grams of soy a day instead of animal protein reduced LDL cholesterol by about 13 percent, and also reduced total cholesterol and triglycerides.
  • Osteoporosis: Because the isoflavones in soy can act like weak estrogens in the body, scientists theorized they could help post-menopausal women avoid the effects of menopause, one of which is bone loss. Laboratory studies showed these isoflavones could support the maintenance of bone, and some studies suggested they could help support bone mineral density in postmenopausal women.
  • Menopause: Again, because of their estrogenic activity, isoflavones were believed to help dilute the symptoms of menopause. Some studies seemed to support this theory. In a 2001 study, for example, researchers found that in Japanese women, soy intake reduced the occurrence of hot flashes. A later 2012 review of 19 trials reported that consuming soy isoflavone supplements for six weeks to 12 months significantly reduced the frequency of hot flashes by about 20 percent compared to placebo. The study also showed that the isoflavones reduced the severity of those hot flashes that did occur by about 26 percent.
  • Diabetes: Some studies showed that a diet high in legumes (including soybeans) could help reduce risk of type 2 diabetes. In 2008, for instance, researchers followed nearly 65,000 women with no history of type 2 diabetes, and found that those who ate more peanuts, soybeans, and other legumes were less likely to develop type 2 diabetes as they aged.

Considering all these benefits, food manufacturers saw a cash cow. Soon the grocery store aisles were lined with just about every soy product you could think of, from milks to meatless burgers to tofu to edamame to soy nuts and more.

Of course, in America, if some is good, more must be better, so we soon had soy protein showing up in just about everything, including pasta, breakfast cereal, baked goods, whipped toppings, meat products, imitation cheeses, yogurt, and more.

But Wait…

Then the other shoe dropped. As always happens with food fads, new studies poked holes in soy’s previous stellar healthy reputation.

  • Soy Doesn’t Really Help Prevent Heart Disease or Cancer: In a 2006 study, researchers reviewed the current literature, and found that while 50 grams a day of soy (about 8 glasses of soy milk or 1.5 pounds of tofu) did reduce LDL “bad” cholesterol, it was by less than three percent. Meanwhile, soy had no effect on HDL “good” cholesterol or triglycerides. They added that it was not established that soy could help prevent or treat breast or prostate cancer, and that some studies had shown it could actually have an adverse effect. Finally, they stated that soy protein and isoflavones were not shown to reduce symptoms of menopause, and concluded that the use of isoflavones in food or supplements “is not recommended.”
  • The Jury is Still Out on Soy and Menopause: In theory, soy’s isoflavones could provide an estrogen boost during menopause, helping to reduce symptoms like hot flashes. So far, study results have been mixed. A 2004 review of 25 clinical trials concluded that phytoestrogens from soy foods, soy extracts, and red clover extracts did not improve hot flashes or other menopausal symptoms. An earlier 2002 review of 29 studies found similar results. A 2012 meta-analysis, though, as noted above, did find that soy extracts could help. (The extracts contained at least 54 milligrams of soy isoflavones.)
  • We Still Have No Solid Evidence on Soy and Cancer: According to the American Cancer Society, human studies are under way to determine if the isoflavones in soy may yet prove beneficial against breast, endometrial, and prostate cancer. The University of Maryland Medical Clinic adds that while Asian women may enjoy reduced cancer rates because of soy, Western women receive only a small benefit, if any at all. For now, we have no solid evidence that consuming extra soy helps prevent or treat cancer, and there is some evidence that it could cause harm, particularly in post-menopausal women.
  • Soy Doesn’t Help with Osteoporosis: Despite the promise of early laboratory and epidemiological studies, more recent research has found no reliable evidence that soy can help postmenopausal women avoid bone loss.
  • It’s Unclear Whether Soy Helps with Diabetes: We have mixed results on soy and diabetes, as well. A 2010 study, for instance, found that soy supplements did not improve blood glucose control in women with prediabetes, or women diagnosed with type 2 diabetes. A 2009 study, though, reported that foods rich in soy isoflavones decreased blood glucose levels and improved glucose tolerance in those with diabetes. A later 2014 study also found that soy protein supplements improved blood pressure in men with type 2 diabetes.
Might Soy Cause Harm?

In addition to the mixed results on soy and its potential health benefits, we have some evidence that certain forms of soy may be linked with some health problems.

  • Thyroid disease: Could consumption of soy could have negative affects on the thyroid? A small 2011 study found that patients who already had “subclinical” hypothyroidism who consumed soy protein (30 grams—a realistic daily intake for vegetarians and vegans) were at a higher risk of developing overt hypothyroidism. A 1990 study also found an association between soy formula feedings in infancy and an increased risk of autoimmune thyroid disease later in life. Other studies have found that soy can suppress thyroid function.
  • Digestive issues: There’s also some evidence that GMO soy can cause digestive inflammation, and may result in symptoms like constipation and diarrhea. A 2013 study found that pigs fed a combination of GMO soy and corn suffered more frequent severe stomach inflammation than those who ate a non-GM diet. Because human and pig digestive systems are similar (really!), researchers suggested further study. Soy is also known to contain protease inhibitors that suppress some key digestive enzymes. Some studies have also suggested these inhibitors to be linked to pancreatic cancer.
  • Cancer: Some animal and human studies have shown that soy can encourage the growth of breast cancer, but these were usually conducted with isolated soy protein, not with natural soybeans. Still, this is a concern, as isolated soy protein is present in many of today’s processed foods. Studies on women consuming natural soy foods typically show a reduced risk of breast cancer.
  • Male hormone issues: Some animal studies have shown that soy isoflavones in the womb may negatively affect sexual development in males. Studies on soy and testosterone levels in adult males have been mixed, with some showing that large amounts of daily soy can reduce testosterone and semen quality, and others showing no effect.
Recommendations for Today’s Healthy Diet

We know that in its basic, wholesome form, soy is just as nutritious as other beans. It’s high in protein and fiber, low in fat, and is a good source of vitamin B, calcium, vitamin K, and omega-3 fatty acids.

But like so many of today’s foods, the soy we’re most often presented with in our modern-day diet has been messed with in a number of ways that may alter its composition and potentially cause health problems. Soy protein, for example, is made from what’s leftover after soybean oil is processed, and then further processed to make it work in milks, baked goods, cereals, and more. All this processing robs soy of its natural compounds that are likely to create health benefits.

On top of that, soy is everywhere—soy protein, soy oil, and other processed soy products appear in all sorts of today’s foods. If you’re eating protein bars, cereals, bottled dressings, vegan meat substitutes, fast foods, and mayonnaise, you’re probably consuming some form of soy in all of those.

Considering everything we know so far, we can come up with the following guidelines for enjoying soy in our daily diets:

  • Go natural: Choose only the whole food (soy beans), and make sure you’re getting non-GMO. Look for organic.
  • Choose fermented: Fermented soy is easier on the digestive system, boosts beneficial bacteria in the gut, and is also the preferred form of the food in Asian populations, which seem to benefit from soy. Choose miso, tempeh, fermented tofu, and natto.
  • Ditch the extra soy products: The reality is we can all end up consuming more soy than we think because it’s so ubiquitous in our foods. Read labels, and try to avoid all the excess soy in your daily diet. Look for terms like: soy oil, soy protein isolates, soy protein, soy lecithin, and textured vegetable protein (TVP). Always buy organic. Choose grass-fed beef.
  • Think moderation: A bit of edamame on your salad, a splash of non-GMO soymilk in your coffee, or other healthy forms can be good for you, but think moderation when approaching soy in your diet.
  • If you have thyroid disease: You may want to avoid soy entirely.
  • If you’re sensitive: If you experience digestive symptoms after eating soy, try consuming some digestive enzymes with it, or you can choose to avoid it.
  • If you have cancer: Those already fighting an estrogen-based cancer like breast cancer or prostate cancer may want to avoid soy to reduce the risk of any potential increase in estrogen-like activity.
  • What do you think of the research on soy so far? Do you avoid it or include it for its natural health benefits?

    * * *

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    Frank M. Sacks, et al., “AHA Science Advisory: Soy Protein, Isoflavones, and Cardiovascular Health: An American Heart Association Science Advisory for Professionals from the Nutrition Committee,” Circulation, 2006; 113:1034-1044,

    Badger TM, et al., “Soy protein isolate and protection against cancer,” J Am Coll Nutr., April 2005; 24(2):146S-149S,

    Hakkak R, et al., “Diets containing whey proteins or soy protein isolate protect against 7,12-dimethylbenz(a)anthracene-induced mammary tumors in female rats,” Cancer Epidemiol Biomarkers Prev. January 2000; 9(1):113-7,

    Nagata C, “Ecological study of the associatio between soy product intake and mortality from cancer and heart disease in Japan,” Int J Epidemiol., October 2000; 29(5):832-6,

    Zhang X, et al., “Soy food consumption is associated with lower risk of coronary heart disease in Chinese women,” J Nutr., September 2003; 133(9):2874-8,

    Cesare R., et al, “Soy Proteins and Cardiovascular Disease,” Current Ahterosclerosis Reports, 2001; 3(1):47-53,

    Anderson JW, et al., “Meta-analysis of the effects of soy protein intake on serum lipids,” N Engl J Med., August 3, 1995; 333(5):276-82,

    De Lemos ML, “Effects of soy phytoestrogens genistein and daidzein on breast cancer growth,” Ann Pharmacother. September 2001; 35(9):1118-21,

    Allred CD, et al., “Soy diets containing varying amounts of genistein stumulate growth of estrogen-dependent (MCF-7) tumors in dose-dependent manner,” Cancer Res. July 2001; 61(13):5045-50,

    Krebs EE, et al., “Phytoestrogens for treatment of menopausal symptoms: a systematic review,” Obstet Gynecol. October 2004; 104(4): 824-36,

    Kronenberg F, Fugh-Berman A., “Complementary and alternative medicine for menopausal symptoms: a review of randomized, controlled trials,” Ann Intern Med. November 19, 2002; 137(10):805-13,

    Atmaca A, et al., “Soy isoflavones in the management of postmenopausal osteoporosis,” Menopause, Jul-Aug 2008; 15(4 Pt 1):748-57,

    Chisato Nagata, et al., “Soy Product Intake and Hot Flashes in Japanese Women: Results from a Community-based Prospective Study,” Am. J. Epidemiol. 2001; 153(8):790-793,

    Taku K, et al., “Extracted or synthesized soybean isoflavones reduce menopausal hot flash frequency and severity: systematic review and meta-analysis of randomized controlled trials,” Menopause, July 2012; 19(7):776-90,

    Sathyapalan T, et al., “The effect of soy phytoestrogen supplementation on thyroid status and cardiovascular risk markers in patients with subclinical hypothyroidism: a randomized, double-blind crossover study,” J Clin Endocrinol Metab. May 2011; 96(5):1442-9,

    Fort P, et al., “Breast and soy-fromula feedings in early infancy and the prevalence of autoimmune thyroid diseaese in children,” J Am Coll Nutr., April 1990; 9(2):164-7,

    Monica Eng, “Pigs fed GM grain suffer health problems, study says,” Chicago Tribune, June 11, 2013,

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    Diane Fennell, “No Diabetes Benefit from Soy Supplements: New Study,” Diabetes Self Management, April 23, 2010,

    Endocrine Society, “Soy supplements appear to be safe, beneficial in diabetic men,” Science Daily, June 23, 2014,

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    Colleen M. Story

    Colleen M. Story

    Colleen M. Story, a northwest-based writer, editor, and ghostwriter, has been creating non-fiction materials for individuals, corporations, and commercial magazines for over 17 years. She specializes in the health and wellness field, where she writes and ghostwrites books, e-books, blogs, magazine articles, and more.

    Colleen is the founder of Writing and Wellness. Her fantasy novel, “Rise of the Sidenah,” was released with Jupiter Gardens Press in September 2015. Her literary novel, “Loreena’s Gift,” is forthcoming in spring 2016 from Dzanc Books. She lives in Idaho.


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    1. I had a terrible experience with soy many years ago; I have Hashi’s and as it was the only change I had made I was able to correlate what was happening to me to what I was ingesting. My health seriously deteriorated, albeit slowly, during the time I was drinking soy milk; about 4-6 times daily in ~ 12 oz. servings. In retrospect, the soy milk I was drinking was in all probability gmo soy milk, which may have been the critical difference; not really sure. I found this article to be well done and well balanced. These days I only use fermented soy products and I make darn sure that they are organic! I will not take any more chances. I use it in moderation only; it is not a daily thing for me.

    2. Peter says:

      Thanks, good report.
      Organic, pure soymilk, just soy, nothing added or make it yourself – then in moderation is great – it is also great in taste!

    3. Diane says:

      I would love to see a digest of the preparation methods for the soy that is consumed in the western diet and how it has changed over time and in different markets. If I understand correctly, most of the soy consumed in eastern diets is either fermented or prepared as tofu, whereas in western diets this is more heavily skewed towards milk consumption. When I was young (think 1950s) we ate a soy-enriched bread that was quite brown in colour. The brown, as it was explained to me, had to do with the use of heat in the preparation of the soy flour, which had the effect of denaturing some of the phytoestrogens and other compounds that are now recognised as not being beneficial. However, brown colouration in soy milk is not looked upon favourably by marketers, and there was a progression towards lesser treatments that produced lighter-coloured milk. Is it possible that one could report benefits from consuming soy prepared in one way, but harm (or lack of benefit) when consuming soy milk produced in another?
      It would be fascinating to discover whether it is the change in preparation method that has brought about this apparent flip-flop in research results. Anyone have any more information?

    4. Liz says:

      I like all things soy & even used to make my own tofu. But since the soy market in the US is so heavily GMO, I’ve chosen to give it up. If the GMO situation shows drastic improvement I’ll have to examine the latest research available at that time.

    5. Martina says:

      Up until last June I had absolutely terrible digestive problems for 15 years, having tried just about every remedy (apart from prescription GERD drugs) and finding nothing relieved the (often quite embarrasing) symptoms. If a had a single coffee or glass of wine on an empty stomach I’d have hiccups and reflux for hours. I spent many thousands on my teeth as acid reflux had destroyed enamel. On a GERD help site I read a recommendation to stop drinking soya milk a few days and see if that made a difference. I had drunk non-GMO soya every day for 15 years (yes – in hindsight “DUH’OH!!”). i switched to coconut and almond milk. Within 48 HOURS all; yes, every bad symptoms vanished. I was incredulous!! The answer was that simple!! I have never felt better and would now not go near a soya product (unless fermented) with a barge pole. In my experience soya milk and tofu have been the most unhealthy products I have ever eaten.

    6. Michele Shohatovitz says:

      It more simple than people think.
      Like everything else in todays food industry the answer is very simple:
      The less processed the soy bean (this includes genetic changes) then healthier it is.
      I must also add its a matter of the correct moderation. In other words a healthy 20 year old girl has different needs than a menopausal 51 year old. Food is an means to an end- it helps you live or can help you die. The amounts of proteins and type of proteins is different for a 20 year old than a 51, 70, and 80 year old….
      This is the same for all kinds of foods. One persons medicine is another persons poison.
      Variation is a must for good health!
      The advice I give to all my clients in my clinic is :
      The rule is this try to feel your needs, listen to your body, and eat real whole foods closer to the way mother nature gave us further from man made foods.

    7. Sondra says:

      Even in natural foods moderation and variety is a wise course.
      It is beneficial to seek nutrients from different whole foods rather
      than relying on just a few.

    8. Soy, like wheat and corn, seems to be one of those things that’s hard to completely avoid but I do so as much as possible by reading labels on “everything”.

    9. Linda says:

      From everything I have read, soy beans need to be fermented to become digestable. So I only consume tempeh in small amounts twice a week. I would rather eat fresh green beans from my organic garden.

    10. Jane Guyette says:

      It is my understanding from the research that soy does not mimic estrogen as you suggest, but shares the same estrogen receptor. The benefit of soy is that because it binds to those receptors, it doesn’t allow the harmful chemicals that do act like estrogen to bind to those sites producing high estrogen effects. It essentially uses up the estrogen receptor sites protecting us from other harmful chemicals.

      I do use organic and fermented soy products periodically.

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