Soy Isoflavones: Superfood or Toxic Killer?
Imagine walking into a room where there were crop farmers dressed in head-to-toe John Deere green giving what-for to dairy farmers, in their high rubber boots and workman’s gloves.
Would you walk away, thinking they were crazy and completely removed from you and your life?
What if it was suit-clad lobbyists representing each group of farmers? Still think it wouldn’t apply to you? You’d likely assume they were battling over farm land, acreage, and other stuff than has nothing to do with you.
But you’d be wrong.
They are arguing over the benefits and dangers of soy. And they are going out of their way to convince you that soy is either the messiah of health or the devil itself. So who’s right?
The Controversy about Soy…
When it comes to soy, there are VERY strong opinions on both sides of the table. On one side, you have the soy advocates touting soy for its menopause and heart-protective benefits.
On the other side, you have the naysayers claiming that soy increases your risk for female-related cancers, thyroid complications, and digestive upset.
Then, add to the already murky waters the fact that many of the pro-soy studies are funded, in part, by John Deere and other companies that have a vested interest in soy production.
On the flip side, some of the anti-soy studies are funded, in part, by the dairy lobby, which has an interest in less soy, more dairy.
Given all this, the only thing to do is to look at the facts and review the studies on each side.
Soy advocates point to two key areas that this controversial bean may show some benefits: decreasing cholesterol levels and relief from menopause symptoms. Let’s first take a look at the cholesterol claims.
Can Soy Help Improve Your Cholesterol?
Advocates point out that more than 30 clinical studies have been performed since 1968, all showing that soy is highly effective for decreasing cholesterol levels. A meta-analysis from the New England Journal of Medicine1 confirmed these findings.
After reviewing 38 placebo-controlled clinical trials, researchers concluded that individuals who consumed an average of 47 grams of soy protein per day had a 13 percent decrease in LDL cholesterol, a 10.5 percent decrease in triglycerides, and a 9 percent decrease in total cholesterol levels.
While this is clearly strong support in favor of soy’s ability to lower cholesterol levels, what it doesn’t lay out is the form of soy protein. Was it a powder? The actual soybean itself? Tofu (soybean curd) or tempeh (fermented soy)? Or was it a textured, processed soy food? As odd as it may sound, the form of soy really does matter…as you’ll soon see.
In another study2, researchers gave 42 participants with high LDL cholesterol levels four different diets, fed in randomized order for six weeks at a time over the course of 24 weeks. Diets contained:
At least 25 grams of animal protein a day,
- At least 25 grams of isolated soy protein,
- Trace amounts of soy isoflavones, or
- 50 mg of soy isoflavones.
Researchers found that soy significantly reduced total and LDL cholesterol and triglyceride levels in participants with very high cholesterol levels. However, it had only a modest effect on those participants with elevated, but not severely high, cholesterol.
They concluded, “Although potentially helpful when used to displace products containing animal fat from the diet, the regular intake of relatively high levels of soy protein had only a modest effect on blood cholesterol levels and only in subjects with elevated LDL cholesterol levels. Soy-derived isoflavones had no significant effect.”
In other words, eating soy (but NOT taking a supplement) helps those people with elevated cholesterol, but doesn’t really help someone with moderately high cholesterol.
What the researchers fail to mention is that simply reducing the consumption of animal protein (particularly with no regard for the quality of that animal protein), regardless of the soy substitute, may have had the same effect. It would be interesting to see the results of that type of study.
A similar study from the November 2001 issue of Archives of Internal Medicine3 followed more than 9600 men and women for 19 years. They found that those who ate legumes (all legumes, not just soy) four times or more per week compared with less than once a weekwas associated enjoyed a 22 percent lower risk of coronary heart disease and an 11 percent lower riskof cardiovascular disease.
Researchers concluded that increased legume intake may be an important part of a dietary approach to preventing CHD.
What is interesting about this study is that it includes ALL legume consumption, not just soy. And since legumes (beans, peas, etc.) are high in fiber, it could be the legumes themselves, not the soy per se, that is responsible for the decreased risk of heart disease.
Still, it was these types of studies that, in 1999, led the FDA to authorize of the use of health claims on the labeling of foods containing soy protein.
The ruling was based on research that suggested such foods might reduce risk of coronary heart disease by lowering blood cholesterol levels.
According to the FDA, foods must contain 6.25 grams per serving of soy protein in order to qualify for the claim, and a daily intake of 25 grams is recommended to achieve a significant cholesterol-lowering effect.
While the studies surrounding cholesterol and soy are compelling, there are serveral obvious holes some the studies and questions remain. Let’s see if the studies around soy and menopause symptoms can help answer those questions.
Can Soy Help Ease Menopause Symptoms?
On the menopause front, there are also good studies showing that soy helps to alleviate menopause symptoms. In fact, its effects are similar to that of a drug, something we’ll discuss in a second.
In one double-blind, randomized, placebo-controlled study4, researchers divided 180 menopausal women into two groups. The first received 80 mg soy isoflavones and the other received a placebo. At the end of 12 weeks, those taking the soy isoflavones reported a 41.2 percent reduction in hot flashes, as compared to a 29.3 percent reduction in the placebo group.
The soy appears to be more effective than placebo at reducing hot flashes. While the results appear to be promising, there is only a 12 percent difference in the results.
Which makes us wonder, how would soy stack up against something known to reduce hot flashes? Researchers at the State University of Campinas, Brazil, wondered the same thing.
Researchers there performed a double-blind, randomized, placebo-controlled study on 60 healthy, postmenopausal women5. Their goal was to see if soy worked as well as conventional hormone therapy at relieving menopause symptoms.
They divided the women into three groups. One received 90 mg of soy isoflavones, one received 1mg estradiol and 0.5 mg of noresthisterone acetate, and the third received placebo.
At the end of 16 weeks, researchers found a statistically significant improvement in hot flashes, muscle pain, and vaginal dryness in both the estrogen and soy groups. Also, there was no statistically significant difference between these groups.
Researchers concluded, “Dietary soy supplementation may constitute an effective alternative therapy for…symptoms of menopause.”
So, here we have a “gold standard” study indicating that a fairly high dose of soy isoflavones worked as well as conventional hormone therapy at reducing some of the main complaints of menopause, namely hot flashes and vaginal dryness.
But we have to ask the question…is a high dose of soy isoflavones safe? This is the key argument for those opposed to soy. Let’s see what they have to say.
The Argument Against Soy…
On February 19, 1999, two researchers from the Food and Drug Administration (FDA) signed a letter of protest against the FDA’s approval of soy6. They pointed to a number of animal studies showing a connection between soy consumption and many health problems, including cancer.
In their letter, they take issue with soy isoflavones’ estrogenic effects. They point to the fact that soy isoflavones “demonstrate toxicity in estrogen sensitive tissues and in the found 31 dose-response curves for hormone-mimicking chemicals that also fail to show a threshold.”
They go on to say, “Our conclusions are that no dose is without risk; the extent of the risk is simply a function of dose.”
What does this scientific gobbledygook mean? It simply means that tissues that are estrogen sensitive (i.e. breast, uterus, cervix, ovaries, etc.) read soy as an estrogen mimic and as toxic, possibly even cancer-causing.
Moreover, there is no upper or lower dosage that indicates toxicity. And that no matter how much or how little you eat (if the food) or take (if in supplement form), soy always poses a risk.
To put the risk issue into context for you, it would be like swimming in shark-infested waters. Whether you just go in for a five-minute dip or splash around for an hour, you are a risk of getting bitten. Your risk is less if you just jump in then out, but there is a real risk nonetheless.
When listing their reasons for asking the FDA to pull back on their blanket recommendation of soy without discussing the dark side, these concerned FDA researchers point to three specific areas of concern:
- the possible connection between soy and estrogen-dependent cancers,
- a possible link between soy and thyroid issues, and
- the use of soy for infants.
Soy and Cancer…
On the cancer front, soy advocates point to the fact that the Japanese, who eat significantly more soy that Americans, have a lower incidence of breast, uterus, and prostate cancers7.
But, what they fail to mention is that this same Japanese population have higher rates of other cancers, namely esophageal, stomach, pancreatic, thyroid, and liver cancer8, 9. This inconvenient fact is something you almost never hear about.
Also on the cancer front, in a study from the May 2002 issue of Cancer Research10, researchers investigated the interactions between dietary genistein and tamoxifen (an estrogen antagonist used in the treatment of estrogen-dependent breast cancer).
They implanted estrogen-dependent breast cancer cells in mice who had had their ovaries and thymus removed. This is important, because your ovaries and thymus produce estrogen. By removing these, researchers were trying to ensure that any estrogen effects were coming from the soy.
Researchers found that genistein either negated or overwhelmed the inhibitory effect of tamoxifen. Based on these findings, they urged postmenopausal women to exercise caution when consuming dietary genistein while taking tamoxifen.
In other words, women taking tamoxifen to help stop the growth or spread of breast cancer were completely undoing the positive effects of the medicine by eating soy.
Soy and Thyroid Disorders
On the thyroid front, soy opponents like to refer to studies that show that consuming isoflavones may lead to development of thyroid disease…in animals. To highlight this, let’s look at one study that tested the effects of genistein (the major isoflavone found in soy) on thyroid function in rats11.
Researchers gave rats a genistein-fortified diet then tested their thyroid function. They found that “genistein was measured in the thyroid at levels that produced dose-dependent and significant inactivation of rat thyroid peroxidase (TPO)… Furthermore, rat TPO activity was dose-dependently reduced by up to 80 percent.”
In layman’s terms, the soy isolate practically shut down the rat’s thyroid function. But rats, it was a study on just that, rats.. It would be nice to see a study showing this effect in humans.
And the researchers themselves were not blind to this. And yet they concluded that even the possibility that widely consumed soy products may cause harm in the human population is of concern.
The Concern With Soy-Infant Formulas…
While the studies on soy and cancer and thyroid are concerning enough, the issue that has most soy opponents up in arms has to do with soy and infants.
And on this front, one study in particular really presents some shocking findings.
Researchers at the Children’s Hospital Medical Center in Cincinnati, Ohio, performed a random, double-blind study12 to see how much phytoestrogen 21 four-month-old infants received from soy-based formula.
They divided the infants into three groups. One received soy-based formula, one received cow milk formula, and the third had human breast milk. For the soy formulas, researchers tested five different brands, all of which showed similar soy isoflavones content and proportion of soy isolate.
They found that those infants receiving the soy formula had 214 times more genistein (a key isoflavone found in soy) in their blood than found in the infants receiving cow’s milk, and 244 times more than that found in infants receiving breast milk.
The infants receiving soy also had 140 times more daidzen (another key isoflavone in soy) than those found in the infants receiving the cow’s milk formula and 210 times more than in the infants taking the breast milk.
Researchers concluded that the “daily exposure of infants to isoflavones in soy infant formulas is six to 11 fold greater on a bodyweight basis than the dose that has hormonal effects in adults consuming soy foods.”
Worse yet, they go on to say that “circulating concentrations of isoflavones in the seven infants fed soy-based formula were 13,000 to 22,000 times higher than plasma oestradiol concentrations in early life, and my be sufficient to exert biological effects.”
Wow! That’s a lot of unnatural estrogen floating around in those little bodies. And we wonder why girls are developing so much earlier than they did 20 years ago and why boys seem to be behind the curve. Could it be all that excess estrogen?
Finally, those that are opposed to soy also point to the number of soy allergies and digestive problems soy can cause, including gas, cramping, bloating, or intestinal discomfort, that indicate that soy may not be in our best interests..
What Does It All Mean?
The reality is there are good studies on both sides of the fence. Soy does seem to have cardio-protective benefits, and it clearly helps ease menopause symptoms. However, the very reason soy works so well for lowering cholesterol and relieving hot flashes is because it is an effective estrogen mimic.
That being said, it stands to reason it could be a concern for those with estrogen-dependent cancers or thyroid issues. And, most problematic, feeding those estrogens to infants whose little bodies aren’t prepared for the estrogen onslaught.
Or, in the words of those FDA researchers, “While isoflavones may have beneficial effects at some ages or circumstances, this cannot be assumed to be true at all ages. Isoflavones are like other estrogens in that they are two-edged swords, conferring both benefits and risk.”
Therefore, taking a commonsense approach, we side with the soy opponents, and encourage the vast majority of people to avoid soy, especially those with a personal or family history of estrogen-dependent cancer or thyroid disease. And, under no circumstances, use soy-infant formulas.
Another way to think about soy is that whatever benefits there MAY be to consuming soy, those benefits can be replicated through other natural means, such as by consuming other plants that have cardio-protective and cancer-preventing phytochemicals.
Therefore, simple common sense says that if you can get those same benefits naturally somewhere else, there’s little point in consuming something with such well-documented dangers.
The only exception we see for soy is those women going through menopause who DO NOT have any of the following issues:
- personal or family history of estrogen-dependent cancer, such as breast, uterine, cervical, or ovarian cancer;
- thyroid or family history of thyroid disease [link to thyroid article];
- soy allergies; or
- problems digesting soy or other legumes.
For this small population, soy may confer some benefit. If you fit into this group, avoid soy supplements and processed soy foods and limit your soy consumption to organic soybeans (edamame) and organic, fermented soy foods, such as:
- tamari, or
The organic element to soy is critical. Ninety-one percent (yep, 91) of all soybean crops grown in the U.S. are genetically modified.13
In case you aren’t familiar with genetic modification (always referred to as GMO), it means that a company (the largest of whom is Monsanto) genetically alters the plant, usually to be herbicide tolerant. As you can imagine, this creates a whole cascade of health concerns, all of which are hotly debated by the GMO developers and medical researchers.14
Not sure what’s to debate. One animal study alone found that hamsters that were fed a GMO-soy diet for two years (and three generations of hamsters) had not only lost their ability to have babies, but those pups that were born had higher “infant” mortality rates and slower growth. Some of the third generation pups even had hair growing inside their mouths.13
All of this just makes it more and more clear that you should simply say no to soy. If you would think twice about popping a few birth control pills at lunch or slugging back some hormone replacement pills with dinner, then you shouldn’t be using soy either.
Treat soy like the true estrogen it is.
1Anderson, JW et al. “Meta-analysis of the effects of soy protein intake on serum lipids.” N Engl J Med. 1995;333:276-82.
2Lichtenstein, AH et al. “Lipoprotein response to diets high in soy or animal protein with and without isoflavones in moderately hypercholesterolemic subjects.” Arteriosclerosis, Thrombosis, and Vascular Biology. 2002;22:1852-8.
3Bazzano, LA et al. “Legume consumption and risk of coronary heart disease in US men and women.” Arch Intern Med. 2001;161:2573-8.
4Ferrari, A. “Soy extract phytoestrogens with high dose of isoflavones for menopausal symptoms.” J Obstet Gynaecol Res. 2009 Dec;35(6):1083-90.
5Carmignani, LO et al. “The effect of dietary soy supplementation compared to estrogen and placebo on menopausal symptoms: A randomized controlled study.” Maturitas. 2010 Sept 10 [Epub ahead of print].
6Sheehan, DM and Doerge, DR. 1999 Feb 18. Letter to FDA in reference to Docket #98P-0683.
7Natural Medicine News (L&H Vitamins, 32-33 47th Avenue, Long Island City, NY 11101), 2000 Jan/Feb p. 8.
8Harras, A (ed). Cancer Rates and Risks. National Institutes of Health, National Cancer Institute, 1996, 4th edition.
9Searle, CE (ed.). Chemical Carcinogens. ACS Monograph 173, American Chemical Society, Washington, DC, 1976.
10Ju, YH et al. “Dietary genistein negates the inhibitory effect of tamoxifen on growth of estrogen-dependent human breast cancer (MCF-7) cells implanted in athymic mice.” Cancer Res. 2002 May 1;62(9):2474-7.
11Doerge, DR. “Goitrogenic and estrogenic activity of soy isoflavones.” Environ Health Perspect. 2002 June;110 Suppl 3:349-53.
12Setchell, KD et al. “Exposure of infants to phyto-oestrogens from soy-based infant formula.” Lancet. 1997 Jul 5;350(9070):23-7.
13Smith, J. Genetically Modified Soy Linked to Sterility, Infant Mortality in Hamsters. The Huffington Post. April 20, 2010.
14de Vendomois, JS, et al. Debate on GMOs health risks after statistical findings in regulatory tests. Int J Biol Sci. 2010 Oct 5;6(6):590-8.
Incoming search terms:
- soy isoflavones side effects (1459)
- isoflavones side effects (205)
- soya isoflavones side effects (163)
- side effects of soy (156)
- genistein side effects (136)
- side effects of soy isoflavones (131)
- soy isoflavones benefits (108)
- soy isoflavones acne (55)
- soya isoflavones benefits (45)
- isoflavone side effects (41)
Love or Hate this Article?
Either Way, Do These 2 Things Right Now!