Better Body Clinical Nutrition


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Wednesday, March 27, 2024 12:19 PM

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Photo by Mae Mu un


A singular feature of the modern American diet is its reliance on and love affair with myriad forms of cheap industrially processed soy. As Michael Pollan has observed, “A food scientist can construct just about any processed food he or she can dream up” with soy (as well as corn and “a handful of synthetic additives”).

Long-time Wise Traditions readers will know, however, that soy isoflavones inhibit the enzyme thyroid peroxidase (TPO), that plays a key role in thyroid hormone synthesis, and they also interfere with thyroid hormone production: “This interference can cause a drop in thyroid hormone levels, an increase in thyroid stimulating hormone and stress on the thyroid gland,” which is “a prescription for thyroid trouble.” Even one serving of soy food can pack more of a thyroid-inhibiting punch (“up to three times the goitrogenic potency”) as pharmaceutical drugs intentionally designed for that purpose.  A health writer who has reviewed the body of evidence on soy and the thyroid advises caution with all forms of fractionated soy, particularly because these products also are likely to derive from genetically modified (GM) soy.

In the Journal of Medical Case Reports in 2017, Japanese researchers corroborated soy’s role as an “exogenous food” capable of interfering with thyroid hormone production. They presented (to their knowledge) “the first report of the presence of [soy] isoflavone in the serum of a patient with severe hypothyroidism.” The report described the case of a seventy-two-year-old woman who showed up at the hospital with sudden-onset severe hypothyroidism after six months of regularly consuming a processed soy-containing “health drink.” Because the woman was an ongoing patient, the researchers had access to her frozen serum from five time points before the hospital admission and continuing for several months after admission. This allowed them to pinpoint the soy isoflavones as the culprit for the patient’s sudden decline, leading the authors to conclude that “consuming health drinks that include soy isoflavone powder extract can lead to severe hypothyroidism.” After immediate discontinuation of the beverage, the woman’s thyroid markers gradually returned to more normal levels. 

The ringing endorsement of commercial soy by celebrity doctors such as Andrew Weil and Christiane Northrup has helped perpetuate the erroneous belief that products such as soy milk are healthy, but those days may be numbered. In response to a petition submitted almost ten years ago by the Weston A. Price Foundation, the U.S. Food and Drug Administration (FDA) belatedly has proposed revoking food manufacturers’ ability to claim that soy protein reduces heart disease risk. An FDA representative stated, “This is the first time we have considered it necessary to propose a rule to revoke a health claim,” admitting that “the totality of currently available scientific evidence calls into question the certainty” of the supposedly protective soy-heart relationship. This landmark shift from an ordinarily intractable agency is good news not just for heart health but also for thyroid health. In fact, the two are intricately interrelated. Cardiovascular symptoms are “some of the most characteristic and common” signs of thyroid disease, and thyroid dysfunction can explain “changes in cardiac output, cardiac contractility, blood pressure, vascular resistance and rhythm disturbances.”
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