Soy is becoming an increasingly common inclusion in the American diet. Those that want to focus on reducing their intake of meat or animal-based products find soy to be an excellent alternative. This is because soy contains a high amount of protein and provides many benefits such as reducing the risk of heart disease, improving glucose and cholesterol levels, and helps regulate fat. However, despite its many benefits, those with thyroid disease, or at risk for thyroid issues, may need to avoid soy. Being familiar with the thyroid disease and the potentially harmful influence that soy has on thyroid function is an important part of protecting wellness.
What is The Thyroid?
The thyroid is a small gland located in the neck that regulates numerous bodily functions including but not limited to metabolism, mood, and cognitive function. The powerful gland regulates these areas through the production of various thyroid hormones such as T4, T3, and Reverse T3. A lapse in thyroid function or disruption of thyroid hormone activity can have a notable impact on functions throughout the body resulting in many forms of dysfunction.
Reduced thyroid production or poor prevalence of thyroid hormones may result in the development of hypothyroidism. As one of the most common forms of thyroid disease, many Americans experience symptoms related to this type of dysfunction including weight gain, an inability to lose weight, muscle pain and weakness, fatigue, and difficulty thinking clearly – get a full list of thyroid disease symptoms here. Sadly, it appears that soy may contribute to the development of thyroid issues including hypothyroidism.
The Impacts of Soy on the Thyroid
Several studies suggest that consumption of soy can negatively affect thyroid function and disrupt the efficacy of thyroid medications. Soy is categorized as a goitrogen meaning that it has qualities that impede thyroid hormone production and contribute to thyroid enlargement or goiter. Researchers have yet to uncover why, but soy appears to more significantly disrupt thyroid function in women compared to men.
Currently, the thyroid-disrupting mechanisms of soy are not entirely understood. However, research shows that it clearly has an impact. In a 2016 study published in Public Health Nutrition, it was found that the risk of elevated TSH levels was four times higher among individuals who ate two servings of soy every day when compared to those without soy in their diet. Another 2016 article found in the Journal of Clinical Endocrinology and Metabolism showed that eating just 16 milligrams of soy on a daily basis is enough to triple the risk of developing overt hypothyroidism.
Soy contains compounds that may significantly impede thyroid activity. The isoflavones genistein and equol, both found in soy, inhibit an enzyme called thyroid peroxidase. This substance is used in the creation of thyroid hormones. Disrupting thyroid peroxidase activity can limit the number of thyroid hormones produced. Studies suggest that the thyroid-disrupting effects of soy occur when intake of isoflavones found in soy surpass 30 mg per day. This is concerning as recent research indicates that some individuals in the United States consume between 80 to 100 milligrams of soy isoflavones daily, which is likely to trigger notable thyroid disruption.
Iodine is one of the essential minerals used in the construction of thyroid hormones. Goitrogens such as soy inhibit thyroid hormone production because they block the delivery of iodine to the thyroid gland. This can cause a notable decline of thyroid hormone values. As levels decline, a feedback loop prompting greater secretion of TSH is established. When working correctly, this promotes production of thyroid hormones. However, if the thyroid is unable to properly by synthesize thyroid hormone, TSH levels may continue to increase to a dangerous degree resulting in the development of a goiter or other thyroid issues. These problems are typically accompanied by the development of hypothyroidism or hypothyroid-like symptoms.
General Concerns and Benefits of Soy
Depending on individual patient factors soy may be beneficial or harmful to your health. Currently, most people who consume soy are doing more harm than good. That is because the majority of soy used in common products and consumed in our diets contain toxins and disruptive agents such as phytoestrogens. Phytoestrogens mimic the effects of estrogen in both men and women, which can contribute to significant hormonal imbalances and thyroid malfunction.
Some forms of soy can be beneficial. Fermentation increases the number of probiotics found in foods, which contributes to greater gut health and by extension better bodily function. Natto is a specific type of soy commonly consumed in Okinawa, Japan. This fermented soy product is considered exceptionally beneficial because it is filled with probiotics and vitamins such as K2, which supports bone building, brain health, regeneration, and longevity.
Soy Safety as a Thyroid Patient
In some cases, thyroid patients may be able to include soy in their diet. However, the majority likely need to limit their intake or avoid it entirely.
Hypothyroidism is often treated using thyroid hormone replacement therapy. Typically, this involves taking a once daily pill first thing in the morning. Ideally, the thyroid hormones contained in the pill make up for the deficit caused by poor thyroid production. Some studies show that soy impedes intestinal absorption of thyroid medications thereby reducing their effect. This may also cause doses to appear inconsistent as the amount of soy consumed and at what time may influence the efficacy of the medication.
As a general guideline it is best to take thyroid medication on an empty stomach and wait an hour before consuming anything but water. Foods that contain soy should not be eaten within three to four hours of taking thyroid medications. Doing so may interfere with absorption thereby disrupting thyroid function. Furthermore, those with a thyroid issue should limit their soy intake to under three times per week or avoid it entirely.
Support your Thyroid by Practicing Soy Safety
Soy is a natural source of healthy protein that provides many notable benefits. But, as with all things, it is best to enjoy it in moderation. Multiple studies have shown the thyroid-disrupting effects of soy, particularly regarding medication efficacy. If a person has already been diagnosed with thyroid disease or is at risk of developing it, they may need to eliminate soy form their diet entirely. Protect your thyroid and overall health by being mindful of soy intake.
1. de Souza Dos Santos MC et al. “Impact of flavonoids on thyroid function.” Food Chem Toxicol. 2011 Oct;49(10):2495-502.
2. Sathyapalan T et al. “The Effect of Phytoestrogen on Thyroid in Subclinical Hypothyroidism: Randomized, Double Blind, Crossover Study.” Front Endocrinol (Lausanne). 2018 Sep 11;9:531.
3. Sathyapalan T et al. “Soy Protein Improves Cardiovascular Risk in Subclinical Hypothyroidism: A Randomized Double-Blinded Crossover Study.” J Endocr Soc. 2017 Apr 3;1(5):423-430.
4. Sathyapalan T et al. “The Effect of Soy Phytoestrogen Supplementation on Thyroid Status and Cardiovascular Risk Markers in Patients with Subclinical Hypothyroidism: A Randomized, Double-Blind, Crossover Study.” J Clin Endocrinol Metab. 2011;96(5):1442-9.
5. Tonstad, S. et al. “The association between soya consumption and serum thyroid-stimulating hormone concentrations in the Adventist Health Study-2.” Pub Health Nutr. 2016;19(8):1464-70.
6. Divi RL et al. “Anti-thyroid isoflavones from soybean: isolation, characterization, and mechanisms of action.” Biochem Pharmacol. 1997 Nov 15;54(10):1087-96.
7. Doerge DR, Sheehan DM. “Goitrogenic and estrogenic activity of soy isoflavones.” Environ Health Perspect. 2002 Jun;110 Suppl 3:349-53.
8. Dr. Josh Axe, DC, DMN, CNS. “Is Soy Bad for You?” Dr. Axe.