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Soy and the Thyroid

A Look at the Controversy Over Soy and Thyroid Health

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Updated June 30, 2014

Soy and the Thyroid

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

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Who Should Thyroid Patients Believe? What Should Thyroid Patients Do?

Until we have the sort of definitive, rigorous, high-quality experimental and human studies into soy toxicity that soy experts Daniel Doerge and Daniel Sheehan called for, it's not advisable to assume that soy is universally safe for thyroid patients. It's also clear that soy does have the potential to cause thyroid problems in a segment of the population that is susceptible, due to iodine deficiency or other conditions.

If you feel it's necessary to include soy in your diet, here are some guidelines.

  • Be sure that you are not iodine deficient. This is tricky, however, because the only way to really determine if you are deficient in iodine is to have a urinary iodine clearance test. (The process of how to assess iodine deficiency is described well in Dr. David Brownstein's book, Iodine: Why You Need It, Why You Can't Live Without It). Be careful not to just decide to supplement with iodine, without clearly establishing that you are deficient, however, because just as iodine deficiency can trigger a thyroid problem, excess iodine can also aggravate and worsen thyroid problems.

  • If you have elevated thyroid antibodies or autoimmune thyroid disease that is not being treated, be aware that soy can be a trigger for developing hypothyroidism.

  • If you are a thyroid patient with optimized thyroid treatment, and you're still suffering from hypothyroidism symptoms, consider eliminating soy from your diet to see if that helps relieve symptoms.

  • If you are eating soy foods, you may want to avoid genetically-modified soy, until the debate over their safety has been resolved.

  • If you are going to eat soy, select fermented and food forms of soy, for example tofu, tempeh, and miso. Avoid processed soy products -- including soy powders, protein shakes, and other processed forms of soy.

  • Limit soy and isoflavone consumption to less than 30 mg per day, at most. Ideally, limit soy foods to several servings per week.

  • Do not eat soy foods within three to four hours of taking your thyroid hormone replacement medication, to avoid any interference with your thyroid medication.

  • Do not use soy or isoflavone supplements.

  • Be careful about the overall quantity of goitrogenic foods that you consume raw, especially if they are in addition to soy foods, which are known goitrogens.

Keep in mind that soy is one of the most common allergy-triggering foods, so even if it is not affecting your thyroid specifically, it may be triggering symptoms of an allergic response, which can include acne, swelling, a stuffy nose, diarrhea, stomach pains, heart palpitations, skin rashes, itching, hives, swelling in the throat, fatigue, and episodes of low blood pressure.

Also, remember that if you do not have a thyroid gland (due to congenital hypothyroidism or surgery) or you have a totally non-functioning gland (due to radioactive iodine ablation treatment), you don't need to be concerned about the effects of soy on your thyroid gland. Soy can, however, still interfere with absorption of your thyroid hormone replacement medication, so be sure to take your medication at least three hours apart from soy foods.

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