Over 5,000 years ago, soybeans were grown to feed animals and enrich the soil in China. In their non-fermented state, humans do not easily digest soybeans. Nina Plank, author of Real Food, describes the discovery of the fermentation process in China approximately 3,000 years ago that enabled people to begin eating soy. Items such as miso, tempeh, and soy sauce are fermented, and not believed to interfere with thyroid function.
During the past 90 years in the United States, the soybean has gone from a relatively unknown legume designed to feed animals, to an amazing health food designed to replace everything from milk, cheese, hot dogs and turkey. This is a true testament to the juggernaut we call marketing! In a relatively short period of time, we have been led to believe that soy is a wonder food – capable of preventing breast cancer and providing us with a healthy source of protein. Sadly, unless you are consuming soy in it’s fermented form, it is likely doing you more harm than good.
In his book Overcoming Thyroid Disorders, Dr. David Brownstein recommends people at least limit their consumption of non-fermented soy products, but ideally, avoid it all together. The trouble with soy is that it interferes with the body’s ability to convert T4 thyroid hormones into T3 hormones. Fortunately, eliminating non-fermented soy from your diet for one month will allow the body to resolve the hypothyroid symptoms in previously healthy people.
If you are taking thyroid medication, consuming soy milk (such as in your morning coffee or breakfast cereal) within four hours of taking your morning dose of thyroid medication may severely limit the effectiveness of the medication. Therefore, if you find your thyroid medication is not as effective as it once was, examine your diet to see if you have begun consuming more soy – read the labels of the foods you eat as it is often a hidden component.
Of further concern is infant soy formula. While soy milk may be easier for babies to digest, research suggests that it also plays a harmful role in the baby’s production of thyroid hormones. Nina Plank reports that soy formula causes babies to develop hypothyroidism and goiter. It may also “stunt growth and disrupt hormones, sexual development, and immunity.” One soy expert from the Food and Drug Administration called soy infant formula “a large, uncontrolled, and basically unmonitored human infant experiment.” As the first generations to be raised on soy formula have reached adulthood, it seems likely the increased incidence of hypothyroidism may be linked to early consumption of soy formula. Plank says emphatically, “I certainly would not feed soy to babies or children…”
The evidence is clear, non-fermented soy food products interfere with the production of thyroid hormones. Resist the urge to be drawn into the marketing machine that wants us to believe soy is healthy. As the food advocate Michael Pollan urges us, “Don't eat anything your great-grandmother wouldn't recognize as food.”