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How soy can kill you AND save your life...

Posted Sep 17 2008 12:50am 1 Comment

"Eating soy will kill you!"


Well, yes... but only if you're a mouse with no ovaries and no immune system, eating highly processed soy extracts in mega doses that humans were never meant to eat.

Scan some media reports and surf the Internet, however, and you're bound to come across scary claims like:

-  Soy will give you breast cancer...
-  Soy formula is dangerous to babies...
-  Genetically modified soy foods may modify you...
-  Soy foods block your thyroid function...
-  Soy prevents the absorption of minerals and blocks digestion...
-  Tofu causes Alzheimer's disease.

On the other hand, you may also have heard:

-  Broccoli has natural pesticides that will kill you...
-  Grapefruit contains naringenin, a potent compound that can have toxic interactions with medications...
-  Celery contains toxins that damage the immune system...
-  Spinach contains oxalates that bind calcium and prevent calcium absorption...
-  Mushrooms contain toxic compounds that cause cancer...

With mixed messages like these, no wonder so many of us are confused!

Let me clear things up for you. 

I have reviewed reams of research and many claims for and against soy foods.

What have I discovered?

Well, there's some good news and some bad news.

From the studies available, I can tell you that soy is neither as good as the proponents say, nor as evil as the critics claim.  I wish we had more convincing science to report, but we don't.  The key is to take all the available evidence together and see what shakes out.  I have done that for you. 

If you want an excellent, unbiased, scientifically sound review of all the relevant human data on soy, I recommend reading the 100-page report from the Agency for HealthCare Research and Quality entitled, "The Effects of Soy on Health Outcomes" ( ), which reviewed thousands of studies based on rigorous criteria for scientific validity. 

Its conclusion was this:  There is no evidence of significant benefit or harm based on the quality of evidence that exists today. 

So what's a confused consumer to do?  Give up on soy until we know for sure?  Or chow down on soy nuts? 

Don't panic.

To me, there ARE some things we do know about soy, both good and bad.

First, you should know that the amount of soy used in many of these studies was much higher than what we normally consume -- the average dose of soy was equivalent to 1 pound of tofu or 3 soy protein shakes a day.

That's a lot of soy!

Most people just don't eat like that. So when you read negative things about soy, remember that many of those claims are based on poorly designed studies that don't apply to real-world consumption.

You could apply that thinking to other studies, too -- like those that show that broccoli contains natural pesticides or that celery is high in toxins. Sure, those foods might cause you some problems -- but not in the amounts that most of us eat. The same is true for soy.

Now I'd like to talk to you about 4 common claims about soy.

  ==> "Soy causes breast cancer."

Because soy foods contain natural plant compounds (called isoflavones) that appear to work like hormones, some people worry that they could increase hormonally driven conditions like breast cancer.

But that doesn't seem to be the case.

In fact, research findings suggest just the opposite:

- All population studies (studies of groups of people) of soy either show reduced breast cancer risk or no effect.

- The only studies to show increased cancer risk are on mice with no ovaries or damaged immune systems and who eat high amounts of processed soy.

- Studies in mice WITH ovaries and functioning immune systems show inhibition of tumor growth.

- Mice studies may not reflect the effect of soy on humans (in case you didn't notice, mice and humans are not the same species).

- High breast tissue density is linked to a higher risk of breast cancer. Breast tissue density increases with estrogen replacement, but decreases with isoflavone consumption in postmenopausal women. That's a good thing.

- Eating soy foods at an early age (childhood and the teen years) appears to have a significant protective effect against breast cancer.

If you really want to reduce your risk of breast cancer, drink less alcohol and eat less trans and saturated fats - all of these compounds may raise risk in high amounts.

If it's a choice between chicken nuggets and tofu, I recommend tofu!

  ==> "Soy formula could harm a baby's development."

Some 20 million infants have used soy formula since the 1960s -- but some people are concerned that the isoflavones it contains could affect a child's growth and reproductive development.

Yet the only large, long-term study on humans, published in the Journal of the American Medical Association, found that there were no major health differences in 811 men and women between the ages of 20 and 34 who had been fed either soy or milk formula as infants.

More recently, a report issued this year by the National Toxicology Program Center for the Evaluation of Risks to Human Reproduction concluded that there just isn't enough human or animal data to say for sure whether soy formula harms a baby's developmental or reproductive health.

So what should a mother do?

First, breastfeed if at all possible, for as long as possible -- ideally until your child is one year old.

If that's not possible and you have to use soy- or dairy-based formula, don't beat yourself up about it. If there are any risks, they are likely to be very small. Hopefully, continuing research will shed more light on this question.

  ==> "Soy is a thyroid poison."

I think this claim makes a mountain out of a molehill. Yes, there's no doubt that soy can affect your thyroid gland -- the real question is, how much does it take?

If you've read that soy is bad for your thyroid, you're probably reading claims based on a few poorly-designed studies that have been blown out of proportion.

Instead, consider this:

A recent review of the research published in the journal Thyroid found no significant effects of soy on the thyroid -- except in people who are iodine deficient, which is rare in this country.

Another well-designed study in the American Journal of Clinical Nutrition studied the effect of realistic amounts of soy protein on hormones, including thyroid hormone. It found that soy had no significant effects on these hormones.

Based on my assessment of this and other research, I am convinced that normal amounts of traditional soy foods pose no risk to thyroid function.

  ==> "Fermented soy is better than non-fermented soy."

Now here's a claim that DOES have some basis in fact.

That's because soybeans -- along with other beans, nuts, and seeds -- contain compounds called phytates, which bind to minerals inside your body and contain some potentially harmful compounds. 

The Asian cultures that have traditionally consumed soy typically ferment it first. This process breaks soy down and makes it easier to digest. Plus, fermentation adds extra nutrients and probiotics ("good" bacteria) to soy.

For these reasons, I prefer fermented soy foods, like miso, natto, tempeh, tofu and some brands of soy milk.

So, should you eat soy?

My answer is YES -- but with two very important guidelines:

Guideline #1:  Say YES to whole, real soy. The Okinawans are the world's longest-lived people, probably in part because of their diet. For more than 5 millennia, they've eaten whole, organic and fermented soy foods like miso, tempeh, tofu, soy milk, and edamame (young soybeans in the pod). One to two servings a day are fine.

Guideline #2:  Say NO to processed soy. That includes soy protein isolate and concentrates, genetically engineered soy foods (typically made from Monsanto's Roundup soybeans), soy supplements, and soy junk foods like soy cheese, soy ice cream, soy oil, and soy burgers. They don't have the thousands of years of traditional use that whole soy foods do, are processed, and contain unhealthy fats and other compounds. I have real concerns about THESE types of soy.

Yes, good human studies on soy are limited -- but those we do have suggest that soy may help lower cholesterol, prevent cancer, increase bone density, protect the kidneys of people with diabetes, and relieve menopausal symptoms like hot flashes.

Here are some things I want you to remember about soy:

1. The dangers of soy are overstated (and the benefits may be, too).

2. We eat FAR too much processed soy (and processed foods in general). Stay away from those in your diet including soy protein concentrates or isolates, hydrolyzed or textured vegetable protein, hydrogenated soy bean oil, non-organic sources of soy, and soy junk food like soy cheese and ice cream. Don't eat them.

3. Whole soy foods can be a source of good quality protein and plant compounds that help promote health.

4. Eat only organic soy -- stay away from genetically modified versions.

5. Replace soy oil with olive oil, fish oil, nuts, and seeds.

6. Breastfeed your child.  I prefer that no one feed dairy or soy formula to their babies, but if you have to, try not to worry about it.

7. Don't worry about soy's effect and breast cancer if you eat it in the forms and amounts I recommend. It has even shown to protect against breast cancer if you start eating it at a young age.

8. The effects on the thyroid are not significant or relevant unless you are deficient in iodine (which you can easily get from eating fish, seaweed or sea vegetables, or iodized salt).

I'm eager to see more research on the effects of soy on our health. But as we wait for more studies, there's no need to pass up this healthful and delicious food.

Have you experienced any health problem because of eating soy?

Have you experienced any health benefits from consuming soy?

Or do you agree or disagree with any of the arguments about this controversial subject that I've listed?

Let me know your thoughts by posting a comment below.

To you and your good health,

Mark Hyman, MD

Comments (1)
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I have a friend that has just started the Maximized Living Nutrition Plan and in it it has a section that discusses soy. In this chapter they have used Dr Kaayla Daniel, author of The Whole Soy Story, for the basis of why soy is not good and to stay away from everything that has soy in it and my friend has really gone over the edge about this and will not eat anything that has soy in it.  She has given me papers she has copied from the book and that I need to stay away from it as well.

How correct is this woman's research and is her scare tactics reasonable??   (I really do hate those that go out and scare people about things like this.)

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