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The Soy Controversy: Is soy dangerous? Answers for men and women.

by Janel Ovrut, M.S., R.D., L.D.N.


Q. I have a question about the dangers of soy. I'm a man who loves soy products, but I've read about several people who referenced thyroid problems. I did an Internet search and saw all sorts of scare stories—estrogen, cancer, you name it. Could you give some insight?
Robert, Colorado

A. Soy is no stranger to speculation: For all the scare stories, there are equally as many studies showing soy's benefits. In fact, soy is rich in vitamins and minerals and a good source of fiber. It's is also a complete protein, meaning that it's a good meat substitute for vegetarians.

And then you read it can cause cancer.

It's no wonder people are confused!

WORRY #1: Does soy cause thyroid problems?

Soy can affect the thyroid in some people. So can peanuts, strawberries, spinach and sweet potatoes. These are all goitrogens: foods that can promote goiter formation—an enlarged thyroid. If you have thyroid problems, talk to your health-care provider about this issue.

Some goitrogens may also be able to slow thyroid function or even trigger thyroid disease. Research suggests that for soy to have this effect, other factors need to be involved, such as already having a tendency to thyroid disease.

A good rule of thumb is that too much of anything is not healthy. Even in people on medicine for their thyroid, most experts don't say they have to stay away from goitrogens completely.Newsletter

WORRY #2: Does soy cause or affect breast cancer?
In some forms of breast cancer, tumors may grow from contact with estrogen. Soy contains isoflavones, which are weak estrogens, but we don't know whether they stimulate tumors or of real estrogen on the tumor. The latter may actually be beneficial.

More research needs to be done since some studies have even shown soy to lower breast-cancer risk. But until we have more-conclusive evidence, many experts recommend that women who have breast cancer, or have a high risk for breast cancer, limit soy intake.

WORRY #3: Does soy cause male infertility?
The jury is still out on whether soy causes infertility, but many men have both eaten soy and fathered children. Shaky studies have sent mixed messages about soy and a lower sperm count, without taking into consideration other factors such as obesity, which can render males more infertile. It's also unclear what forms of soy men reported they were eating.

Soy obviously needs more investigation. But the bulk of research on humans shows that two to three servings per day for normal, healthy people is safe and possibly even protective of some diseases.

Enjoying all foods in moderation is, after all, one of the keys to good health!

is a registered dietitian working in corporate wellness in the Boston, Mass., area.

Last updated and/or approved: February 2010. Article originally appeared in the September/October issue of the former print magazine.

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Comments (2)add comment
The Bottom Line
written by T Gray , June 07, 2013

...needs more investigation. I hear that a lot. You would think that we have advanced further than that. How difficult is it to study something so simple. Millions of dollars (your tax dollars and donations) are going into medical research, and we still don't have enough data concerning a controversial staple consumed in large quantities all over the world? I understand why the pharmaceuticals are not interested; they don't benefit, but there has to be other stake holders out there.
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Soy causes male infertility, Really?
written by David , September 14, 2011

Chinese, Japanese, Koreans, Thais, in fact all East Asians have been eating Soy products from Soy Sauce, Tufu to Endamame for 5000 years! Over 2Billion of us occupy the Earth today. Do you know the population of China today?
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