The Dark Side of Soy

Is America's favorite health food making us sick?



Image by Mo Riza, licensed under Creative Commons.

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As someone who is conscious of her health, I spent 13 years cultivating a vegetarian diet. I took time to plan and balance meals that included products such as soy milk, soy yogurt, tofu, and Chick'n patties. I pored over labels looking for words I couldn't pronounce--occasionally one or two would pop up. Soy protein isolate? Great! They've isolated the protein from the soybean to make it more concentrated. Hydrolyzed soy protein? I never successfully rationalized that one, but I wasn't too worried. After all, in 1999 the Food and Drug Administration (FDA) approved labeling I found on nearly every soy product I purchased: 'Diets low in saturated fat and cholesterol that include 25 grams of soy protein a day may reduce the risk of heart disease.' Soy ingredients weren't only safe--they were beneficial.

After years of consuming various forms of soy nearly every day, I felt reasonably fit, but somewhere along the line I'd stopped menstruating. I couldn't figure out why my stomach became so upset after I ate edamame or why I was often moody and bloated. It didn't occur to me at the time to question soy, heart protector and miracle food.

When I began studying holistic health and nutrition, I kept running across risks associated with eating soy. Endocrine disruption? Check. Digestive problems? Check. I researched soy's deleterious effects on thyroid, fertility, hormones, sex drive, digestion, and even its potential to contribute to certain cancers. For every study that proved a connection between soy and reduced disease risk another cropped up to challenge the claims. What was going on?

'Studies showing the dark side of soy date back 100 years,' says clinical nutritionist Kaayla Daniel, author of The Whole Soy Story (New Trends, 2005). 'The 1999 FDA-approved health claim pleased big business, despite massive evidence showing risks associated with soy, and against the protest of the FDA's own top scientists. Soy is a $4 billion [U.S.] industry that's taken these health claims to the bank.' Besides promoting heart health, the industry says, soy can alleviate symptoms associated with menopause, reduce the risk of certain cancers, and lower levels of LDL, the 'bad' cholesterol.

Epidemiological studies have shown that Asians, particularly in Japan and China, have a lower incidence of breast and prostate cancer than people in the United States, and many of these studies credit a traditional diet that includes soy. But Asian diets include small amounts--about nine grams a day--of primarily fermented soy products, such as miso, natto, and tempeh, and some tofu. Fermenting soy creates health-promoting probiotics, the good bacteria our bodies need to maintain digestive and overall wellness. By contrast, in the United States, processed soy food snacks or shakes can contain over 20 grams of nonfermented soy protein in one serving.

'There is important information on the cancer-protective values of soy,' says clinical nutritionist Ed Bauman, head of Bauman Clinic in Sebastopol, California, and director of Bauman College. Bauman cautions against painting the bean with a broad brush. 'As with any food, it can have benefits in one system and detriments in another. [An individual who is sensitive to it] may have an adverse response to soy. And not all soy is alike,' he adds, referring to processing methods and quality.

'Soy is not a food that is native to North America or Europe, and you have issues when you move food from one part of the world to another,' Bauman says. 'We fare better when we eat according to our ethnicity. Soy is a viable food, but we need to look at how it's used.'

Once considered a small-scale poverty food, soy exploded onto the American market. Studies--some funded by the industry--promoted soy's ability to lower disease risk while absolving guilt associated with eating meat. 'The soy industry has come a long way from when hippies were boiling up the beans,' says Daniel.

These days the industry has discovered ways to use every part of the bean for profit. Soy oil has become the base for most vegetable oils; soy lecithin, the waste product left over after the soybean is processed, is used as an emulsifier; soy flour appears in baked and packaged goods; different forms of processed soy protein are added to everything from animal feed to muscle-building protein powders. 'Soy protein isolate was invented for use in cardboard,' Daniel says. 'It hasn't actually been approved as a food ingredient.'

Soy is everywhere in our food supply, as the star in cereals and health-promoting foods and hidden in processed foods. Even if you read every label and avoid cardboard boxes, you are likely to find soy in your supplements and vitamins (look out for vitamin E derived from soy oil), in foods such as canned tuna, soups, sauces, breads, meats (injected under poultry skin), and chocolate, and in pet food and body-care products. It hides in tofu dogs under aliases such as textured vegetable protein, hydrolyzed vegetable protein, and lecithin--which is troubling, since the processing required to hydrolyze soy protein into vegetable protein produces excitotoxins such as glutamate (think MSG) and aspartate (a component of aspartame), which cause brain-cell death.

Soy also is one of the foods--in addition to wheat, corn, eggs, milk, nuts, and shellfish--most likely to cause allergic reactions. Most people equate food allergies with anaphylaxis, or a severe emergency immune response, but it is possible to have a subclinical sensitivity, which can lead to health problems over time (and is exacerbated by the lack of variety common in today's American diet).

'People can do an empirical food sensitivity test by eliminating the food for a period of time and reintroducing it to see if there's an immune response, but most don't do this,' says Bauman. 'Genetically modified (GM) soy is the most problematic, and that's probably what most people are eating if they're not paying attention. People can develop sensitivity to a food that has antigens or bacteria not originally in the food chain, as is the case with GM foods.'

Yet avoiding GM soy doesn't mean all is well, Daniel says: 'One question I get all the time is, ?What if I only eat organic soy?' The assumption is that GM soy is problematic and organic is fine. Certainly, organic is better, but the bottom line is that soybeans naturally contain plant estrogens, toxins, and antinutrients, and you can't remove those.'

The highest risk is for infants who are fed soy formula. 'It's the only thing they're eating, they're very small, and they're at a key stage developmentally,' says Daniel. 'The estrogens in soy will affect the hormonal development of these children, and it will certainly affect their growing brains, reproductive systems, and thyroids.' Soy formula also contains large amounts of manganese, which has been linked to attention deficit disorder and neurotoxicity in infants. The Israeli health ministry recently issued an advisory stating that infants should avoid soy formula altogether.

Antinutrients in soy block enzymes needed for digestion, and naturally occur-ring phytates block absorption of essential minerals. This is most worrisome for vegans and vegetarians who eat soy as their main source of protein, and for women in menopause who up their soy intake through supplements.

Soy contains phytochemicals--plant nutrients with disease-fighting activity--called isoflavones. Studies claim isoflavones can mimic the body's own estrogens, raising a woman's estrogen levels, which fall after menopause, causing hot flashes and other symptoms. On the other hand, isoflavones may also block the body's estrogens, which can help reduce high estrogen levels, therefore reducing risk for breast cancer or uterine cancer before menopause. (High estrogen levels have been linked to cancers of the reproductive system in women.)

Although soy's isoflavones may have an adaptogenic effect (contributing to an estrogen-boosting or -blocking effect where needed), they also have the potential to promote hormone-sensitive cancers in some people. Studies on the effects of isoflavones on human estrogen levels are conflicting, and it's possible that they affect people differently. In men, soy has been shown to lower testosterone levels and sex drive, according to Daniel.

Bauman believes processed soy foods are problematic but maintains that soy has beneficial hormone-mediating effects. 'People are largely convenience-driven,' he says. 'We're looking at this whole processed-food convenience market and we're making generalizations about a plant. Is soy the problem, or is it the handling and packaging and processing of the plant that's the problem?

'Primary sources of food are a good thing. Once there was a bean, but then it got cooked and squeezed and the pulp was separated out, and it was heated and processed for better shelf life and mouth feel. Soy milk is second or third level in terms of processing.'

Bauman's eating-for-health approach calls for a variety of natural and seasonal unprocessed whole foods, including soy in moderation, tailored to individual biochemistry and sensitivities. 'Using soy as part of a diet can bring relief for perimenopause, for example,' he says. 'Throw out the soy and you throw out the isoflavones.' (It is possible to obtain plant estrogens to a lesser extent from other foods, such as lima beans or flax.) 'The literature is extensive on the benefits of soy, and that should always be stated, just as the hazards should be. That's science. These studies are not ridiculous or contrived, but take a look at them. Who's funding them?' asks Bauman.

'There are a lot of problems with these studies,' Daniel says, adding that the 1999 heart health claim was an industry-funded initiative. 'Even if there is positive information, and even if these studies are well designed, we need to weigh that against the fact that we've also got really good studies showing the dangers. Better safe than sorry is the precautionary principle. Possible bene-fits are far outweighed by proven risks.'

Daniel and Bauman agree on the benefits of variety. 'My experience as a clinical nutritionist is that people who have a varied diet tend not to get into trouble,' says Daniel.

'We like to demonize certain foods in this society,' says Bauman. 'If you want to find a fault, you'll find it. The bottom line is: What is a healthy diet?'

Reprinted from Terrain (Spring 2007), published by Berkeley's Ecology Center. Dedicated to fine feature writing about environmental issues, Terrain is distributed free throughout Northern California. Subscriptions: $15/yr. (3 issues) from 2530 San Pablo Ave., Berkeley, CA 94702;

Soy 'Nuggets'

Soy milk, curdled and pressed into cubes of varying firmness. Often used as meat substitute. A nonfermented product, tofu contains antinutrients, which can block absorption of essential minerals.

Fermented soybean paste, used in soups and sauces. Rich in probiotics, good bacteria that aid vitamin absorption. Miso is high in sodium but is considered one of the healthiest soy products.

Soybean Oil
To extract oil, soybeans are superheated, ground, pressed, mixed with chemicals, and washed in a centrifuge. Soybean oil accounts for 80 percent of all liquid oils consumed annually in the United States.

Soy Milk
A processed beverage made of ground soybeans mixed with water and boiled, which removes some toxins. Sugar is added to improve flavor. An eight-ounce serving contains up to 35 milligrams of isoflavones, which may change estrogen levels and hormonal function.

Snack Food
Highly processed, a source of trans fat. Check your labels: Potato chips, tortilla crisps, and many other deep-fried things have been cooked in soy oil--straight up or partially hydrogenated.

Whole soybeans pressed into loaves, which are then fermented. Often used as a meat substitute. Tempeh is rich in B vitamins, minerals, and omega-3 fatty acids.

Fast Food
A source of hidden soy. Processed soy proteins extend some burgers and chicken (nuggets, patties, even 'grilled breasts'). Buns contain soy oil and to a lesser extent soy flour and lecithin. Soy oil also appears in dressings and dips, in American 'cheese,' and as the No. 2 ingredient in fries. There's even soy in Big Mac's secret sauce: Soybean oil nets top billing.

Whole soybeans, commonly boiled in the pod and eaten as a snack. Most commercial edamame has been preheated to make digestion easier, but it still contains antinutrients.

Image by Mo Riza, licensed under Creative Commons

Want more? Read the rest of Utne Reader's July/August package on the secrets of soy:

  • How Much Is Too Much?
    Clinical nutritionist Kaayla Daniel on the Dos and Don'ts of soy consumption
    interview by Mary Vance, from Terrain
  • Whole New Diet
    A health-savvy cookbook shows how to get away from processed foods
    by Julie Hanus
  • Biofuel's Big Bean
    How large-scale soy is threatening the environment and a South American way of life
    by April Howard and Benjamin Dangl, from In These Times
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2/4/2014 11:34:24 AM

I can only speak from my personal experience, I have always love tofu, soy milk and soy products but made sure it was moderate and not overloading myself with soy. After getting married, my husband is great fan of soy milk and soy products and we started to take lots of lots of soy in our diet.The result is GYNECOMASTIA for my husband and irregular periods for me. Have been to the doctors, had ultrasounds of the breast, thyroid and the reason is because of Soy, which contains large amounts of ISOFLAVONES that mimic estrogen, am not saying soy is bad but I would suggest not eating too much of soy or for that matter anything, the idea is to have a wide variety of different kinds of foods in moderation. It has been a few days that we stopped soy intake, we should wait and see how it goes.

9/23/2013 6:17:47 PM

I developed a soy allergy after a year of mild soy intake. It does happen and I believe it's because of the way we are over processing soy.

9/22/2013 7:22:11 AM

'We fare better when we eat according to our ethnicity. Soy is a viable food, but we need to look at how it's used.' What is this - diet advice for racists? This article is five screens full of junk science, fear mongering, and plainly bizarre advice such as the quote above.

9/18/2013 1:37:29 AM

I have been living in Japan for 25 years, and although I can't comment on the depressing scene in the US with its GM beans and highly processed forms of soy, I can tell you that although Japanese may not eat tofu daily, contrary to claims I have seem on some websites, they do eat it on a regular basis, and the young beans (edamame) are consumed on a regular basis as well(when in season). (I just ate a small tub of tofu with edamame, chopped tomato and cucumber, and dressing for lunch!) So, based on the fact that they have been doing so for hundreds of years and are among the healthiest/longest living people on the planet, I would say either Japanese physiology is completely different (highly unlikely), the anti-soy studies have been poorly done or are biased, or the problem is US made. My feeling is that the last suggestion is the most likely one, possibly in combination with the second.

9/15/2013 12:15:56 PM

i ve been vegetarian 3 years and my diet, even before that, contained a large amount o soy---like a half-gallon of Silk terribly Vanilla each 5-6 days, soy cheese, soy nuggets, soy, soy, soy, boy. 2 things once reading this article: No, soy hasn't crumpled my physical attraction, to mention the smallest amount. And, two, i feel it is the explanation for my fucking beginner moobs despite my long commitment to exercise. so I abandoned soy a month ago; currently it's beans, almond milk and legumes, till somebody comes around and says those things cause your intestine movements to glow within the more

8/4/2012 2:39:50 PM

'Soy is not a food that is native to North America or Europe, and you have issues when you move food from one part of the world to another,' Bauman says. That's NO SENSE! According to that we should stop eating bananas, pinapple, potatos, tomato and corn in Europe!

jola zandecki
6/22/2012 2:09:52 PM

Interesting article. Although the anecdotal evidence in this article seems to indicate that many individuals are in fact sensitive to soy products, I am not to convinced of the science behind the author’s claims. For a bit more scientific and balanced view on soy I highly recommend folks check out It “is the first non-commercial, science-based website to provide free daily updates on the latest discoveries in nutrition.” To learn more about soy specifically you can follow this link:

drcarlos gonzalez
3/20/2012 12:26:49 PM

There will usually always be critics like Anna520 below (probably works for Soy Silk). If you read all the comments below the majority all report negative experiences with soy.

drcarlos gonzalez
3/20/2012 12:20:11 PM

This is probably the best article on Soy I have come across! Great job!

10/18/2011 1:40:09 PM

Thanks for this! I always love different views.

5/10/2011 12:29:20 PM

I'm rather appalled that Utne Reader would publish such obvious junk science. The only two sources referred to by name -- Daniel and Bauman -- don't strike me as reliable authorities. Bauman in particular doesn't seem to stand up to scrutiny once you actually try to find information about the college he directs (it seems more like a platform for marketing snake oil than the website of an institution for higher learning). Vague references to unnamed "studies" fill the gaps, leaving the reader frightened but unable to follow up on the claims. While a lot of the claims here are incredibly scary, the fact is that when you look at high-quality studies in peer-reviewed journals, soy seems to be much more benign than either its proponents or detractors make it out to be. Probably not the magic bullet for menopause symptoms, but it's not going to kill you either. Here are some places to start: Hamilton-Reeves, J.M., et al. (2009). Clinical studies show no effects of soy protein or isoflavones on reproductive hormones in men: results of a meta-analysis; Hooper, L., et al. (2009). Effects of soy protein and isoflavones on circulating hormone concentrations in pre- and post-menopausal women: a systematic review and meta-analysis; Messina, M. (2010). Soybean isoflavone exposure does not have feminizing effects on men: a critical examination of the clinical evidence.

bob due
4/7/2011 4:52:51 AM

There is a big difference in the way soy is processed. Most of the soy in food and supplements is solvent extracted and done with heat. If the soy is water extracted with LOW heat, then it is a totally different product. I have been using a soy protein powder since 1970 that has been handled this way and would not want to be without it.

3/29/2011 9:00:29 PM

I've been vegan three years and my diet, even before that, contained a ton o'soy---like a half-gallon of Silk Very Vanilla every 5-6 days, soy cheese, soy nuggets, soy, soy, soy, boy. Two things after reading this article: No, soy hasn't dented my libido, to say the least. And, two, I think it's the cause of my fucking beginner moobs despite my lifelong commitment to exercise. Thus I abandoned soy a month ago; now it's beans, almond milk and legumes, until someone comes around and says those things cause your bowel movements to glow in the dark.

1/26/2011 11:30:37 AM

"We should eat according to our ethnicity." What exactly does that mean? Only Latinos should eat tacos? Only South Asians should eat curry? Only Black people should eat watermelon?

12/16/2010 8:33:53 AM

I switched to a daily serving of light soy milk with my cereal, instead of dairy milk which had been making me feel bloated and uncomfortable. I've been drinking soy for just over a year and I have not experienced any digestion problems or decrease in testosterone. After reading this, I will probably do the occasional substitution with almond milk for a little more soy moderation, though I'm not crazy about the taste.

10/13/2010 11:32:04 AM

I have done extensive reading on the pro's and con's of soy. Maybe you should and you too will figure out that soy is not good for Humans or animals to consume. Unless it is fermented as the Asians ferment it. But here it America it is not done that way and that is why it is NOT a healthy food to eat. But to all you doubters, go ahead and eat it. No one is telling you not to, they are just saying it's bad to eat. When you are sick everyday with mysterious ailments and end up with cancer one of the foods to not eat on the list your oncologist will hand you will be "Soy". Thank you Mary for taking the time out of your day to post this insightful blog.

10/13/2010 11:27:06 AM

I have done extensive reading on the pro's and con's of soy. Maybe you should and you too will figure out that soy is not good for Humans or animals to consume. Unless it is fermented as the Asians ferment it. But here it America it is not done that way and that is why it is NOT a healthy food to eat. But to all you doubters, go ahead and eat it. No one is telling you not to, they are just saying it's bad to eat. When you are sick everyday with mysterious ailments and end up with cancer one of the foods to not eat on the list your oncologist will hand you will be "Soy". Thank you Mary for taking the time out of your day to post this insightful blog.

8/18/2009 2:27:53 PM

This is not crazy. I diagnosed myself 10 years ago, with this problem when no doctor could figure it out...I'd basically replaced all cow's milk with soy and was drinking some everyday. I was also eating tofu. After several months, I began experiencing horrible headaches, and seemed to have perpetual PMS symptoms- irritability, bloating, sore breasts, pimples. I was 30 years old and had always been healthy. It became almost debilitating. Then, one day, I was at the gym and saw an ad posted in the locker room aimed at menopausal women. It said that soy mimics human estrogen and that these women could ease their symptoms by taking a soy supplement. It immediately became clear to me that I was experiencing soy overload. I went to my doctor and asked her about my theory. She said it was plausible. So, I stopped consuming soy completely and after two weeks, all of my horrible symptoms vanished. I avoid soy now and always tell other women about this. I think the problem in this country is that we always want to overdo everything- even what should supposedly be a good thing- without asking questions. Don't just throw yourself into one mindset or diet- ask questions first and be cautious. You can't trust the FDA. They are understaffed and unable to protect the public health.

8/12/2009 2:07:34 PM

Hi, This is crazy I cant believe what i just read.I have been drinking and eating soymilk and edamane beans. And other soy products for years.

katherine heicksen
8/17/2008 6:40:29 PM

I would love to see some sources on this one, and on any articles of this type. Its always nice to be able to review the info one's self. Could you post sources?