Expert: Mary Shomon - 10/2/2004

Question
Hi.  Have you read all the internet stuff on how soy is "goitrogenic" and sends people into hypothyroidism?  What do you think of all that info out there on the internet about it? (you can find a lot of it on the westonaprice.org site)

Answer
Isoflavones, the key components of soy that make them so potent as a posible substitute for hormone replacement, mean that soy products, while touted as foods and nutritional products -- often are used and act as like a hormonal drug.

If you have a diagnosed or undiagnosed thyroid problem, or a history of autoimmune disease, overconsumption of soy isoflavones can potentially trigger a thyroid condition. Soy foods can worsen an existing diagnosed thyroid problem in many people. In both cases the symptoms such as fatigue, weight gain, and depression or moodiness are often overlooked and hard to diagnose.

A recent study found that as millions of Americans -- perhaps as many as more than 10 million -- have an undiagnosed thyroid condition. The vast majority of thyroid patients are women over 40. This is the same group that, responding to marketing claims that promote soy as helping to prevent breast cancer, reducing the risk of high cholesterol or heart disease, or as a treatment for symptoms of menopause, are turning to soy foods and isoflavone supplements in vast numbers.

Here is more information regarding soy and its relationship to the thyroid.

FDA's Soy Experts Speak Out Against Soy

"there is abundant evidence that some of the isoflavones found in soy, including genistein and equol, a metabolize of daidzen, demonstrate toxicity in estrogen sensitive tissues and in the thyroid. This is true for a number of species, including humans.

Additionally, isoflavones are inhibitors of the thyroid peroxidase which makes T3 and T4. Inhibition can be expected to generate thyroid abnormalities, including goiter and autoimmune thyroiditis. There exists a significant body of animal data that demonstrates goitrogenic and even carcinogenic effects of soy products. Moreover, there are significant reports of goitrogenic effects from soy consumption in human infants and adults."

Official Letter of Protest to the FDA Letter of protest from researchers Daniel Doerge and Daniel Sheehan, two of the Food and Drug Administration's (FDA) key experts on soy, to the FDA, protesting the health claims approved by the FDA on soy products

America's Foremost Alternative Doctor Warns Re: Soy

America's leading alternative doctor, Dr. Andrew Weil, has said about soy, at his Ask Dr. Weil website

"…you're unlikely to get too many isoflavones as a result of adding soy foods to your diet -- but you probably will take in too much if you take soy supplements in pill form. At this point, I can only recommend that you avoid soy supplements entirely."

David Zava, Ph.D., a biochemist and an experienced breast cancer researcher stated in an interview:

"In studying the literature on soy I found there are about five types of plant chemicals in the soybean that can be toxic to humans if they are not removed by special processing… the fifth antinutrient in soybeans is called a goitrogen. This is a chemical that latches on to iodine, preventing it from absorbing into the body from the gastrointestinal tract. Iodine is needed to make thyroid hormone. Low thyroid function has been associated with poor brain development. Anyone who has been deficient in thyroid hormone understands quite well what impact this can have on normal brain function, especially at a time in life as we grow older and "fuzzy thinking" creeps into our vocabulary."

North American Menopause Society Won't Endorse Soy Products

In a press statement, the North American Menopause Society has said:

"Our review found that scientific data are inconclusive regarding whether the observed health effects in humans are attributable to isoflavones alone or to isoflavones plus other components in whole foods… women may wish to consume whole foods that contain isoflavones, especially for potential cardiovascular benefits.

However, scientific data supporting the use of isoflavones for hot flashes are conflicting, and inadequate data exist to evaluate their effect on breast and other female cancers, bone mass and vaginal dryness… Our evaluation also pointed out that a level of caution needs to be observed, especially in the use of isoflavone supplements, powders and pills…More studies documenting benefits and safety need to be conducted."

Also, I've written quite a bit about the goitrogenic and estrogenic effects of soy at my website http://thyroid.about.com and in my books.

Hope that helps

Mary