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Soy and the Thyroid

A Look at the Controversy Over Soy and Thyroid Health


Updated June 30, 2014

Soy and the Thyroid

There is a continuing controversy over whether soy foods can be harmful to thyroid health.

Mary Anthony, a pro-soy researcher at Wake Forest University School of Medicine in Winston-Salem, NC, told the Los Angeles Times: "There's a tendency in our culture to think if a little is good, then a lot's better. I personally am very concerned about isoflavone pills and soy protein supplemented with extra isoflavones. Isoflavones, after all, seem to act like hormones or drugs in our body--even if for regulatory purposes they are classified as nutritional supplements."

In my book "Menopause Thyroid Solution," nationally-known holistic nutritionist Dr. Annemarie Colbin, said that she feels soy may be oversold. Says Dr. Colbin:

I find it interesting that there's such a push for soy as a health food ever since soybeans became genetically engineered. These big companies have a huge marketing machine. I would not use any of the imitation meat soy foods, or any soy that is extruded, extracted, or genetically engineered. Just miso, a little tofu, tempeh...occasionally.
The issue of genetically modified soy is also controversial, as the corporations that are farming soy claim that genetically modified organisms (GMO) in foods -- including soy -- are safe. At the same time, some nations in Europe are banning or severely restricting use of GMO foods, due to concerns about the potential effects GMO foods may have on health, including causing allergic responses, contributing to antibiotic resistance, producing new toxins, concentrating toxic metals, enhancing the growth of toxic fungi, and molecular or DNA damage. In the U.S., various experts and organizations, including consumer watchdog Public Citizen, holistic physician Dr. Joseph Mercola, and environmental group Greenpeace, among others, have serious concerns about GMO foods, including soy. Activist and author Jeffrey K. Smith's bestselling book "Seeds of Deception" chronicles many of the scientific concerns about GMO foods, and pushback from industry.

Is Soy Actually Safe for the Thyroid?

On the other side of the controversy are those who wholeheartedly support soy. Proponents of soy point to a recent study, frequently touted as evidence of soy's safety for the thyroid, which was published in 2006 in the journal Thyroid. The researchers looked at 14 trials involving soy, and in 13 out of 14 trials, either no effects or modest changes were noted in thyroid function as a result of soy consumption. The researchers claim that the findings provide little evidence that "in euthyroid, iodine-replete individuals, soy foods, or isoflavones adversely affect thyroid function."

The researchers also stated that "there remains a theoretical concern based on in vitro and animal data that in individuals with compromised thyroid function and/or whose iodine intake is marginal soy foods may increase risk of developing clinical hypothyroidism. Therefore, it is important for soy food consumers to make sure their intake of iodine is adequate." They also claim that "some evidence suggests that soy foods, by inhibiting absorption, may increase the dose of thyroid hormone required by hypothyroid patients."

This study is suggesting that soy is safe -- unless you have a thyroid condition, or iodine deficiency. It also suggests that soy foods can inhibit absorption of thyroid medication.

The study also goes on to say that despite these factors, soy foods are in fact safe, and all that is needed is to ensure sufficient iodine in the diet along with regular retesting and dosage changes of thyroid medication to make up for any effect the soy has on the thyroid medication.

The study doesn't address the fact that it's estimated that as much as one-fourth of the U.S. population is now iodine deficient, and that the number is on the rise. At the same time, many millions of Americans also have undiagnosed autoimmune thyroid disease. At minimum, if you accept the premise of this study, that means that more than 75 million Americans with iodine deficiency may be at risk of thyroid problems from soy consumption. If you include the up to 60 million Americans who have a diagnosed or undiagnosed thyroid condition, almost half of all Americans could be at risk of soy-related thyroid problems.

It's also troubling to note that the author of this study -- and several other recent studies claiming soy is not a danger to the thyroid, is Mark Messina, PhD. Messina, though not a medical doctor, also goes by the name "Dr. Soy." Messina had been in charge of grant funding at the National Institutes of Health (NIH), where he oversaw a $3 million grant for soy studies. Soon after he left NIH, he was hired to serve on the scientific advisory boards of both the United Soybean Board, and international soy agribusiness Archer Daniels Midland. He still serves on both scientific advisory boards as a paid advisor. In addition to his work on these advisory boards, Messina is a consultant to the United Soybean Board and editor of its soy-related newsletter, and serves as a paid speaker and consultant to promote the positive benefits of soy for the United Soybean Board's "Soy Connection.". Messina has also published a number of books promoting soy. The "Political Friendster" website, which tracks corporate influence, has documented the close relationship between Messina and the various corporate players in the soy industry.

So, is the study accurate? Honestly, it's impossible to say at this point. There is a clear ethical and financial conflict of interest in commissioning research on soy's safety from someone who is a longstanding representative of, and who is lucratively employed by, the soy industry itself.

Hopefully, more studies will be done by researchers who do not have any ties to the industry, or who do not have a vested interest in presenting a rosy picture of soy vis a vis thyroid concerns.

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