Soyfoods, Iodine and Thyroid Function in Vegans

Many foods—including soy, broccoli, and millet—contain goitrogens, which are compounds that interfere with thyroid function. Most people can eat these foods regularly without problems. Problems do occur in people who have low intakes of the mineral iodine, which is needed for a healthy thyroid.

In the 1950s approximately 10 cases of goiter—a symptom of thyroid problems—were identified in infants consuming soy infant formula. These 50-year-old studies have been used to fuel arguments that soy is dangerous for infants—but in fact, they have no relevance to infants who are currently fed soy infant formula. Today’s formula is fortified with iodine and is processed differently than older formulas. As a result, there has not been one case of goiter reported in the medical literature in the more than 20 million babies fed soy infant formula over the past 40 years.

Soy doesn’t adversely affect thyroid function in healthy adults either. As long as people meet the recommendations for iodine intake, consuming large amounts of soy has not been shown to have adverse effects. Whether soy is harmful to those who have deficient iodine intakes hasn’t been determined. But if this turns out to be the case, the answer will be to consume adequate iodine, not give up soy.

This can be a relevant issue for vegans, however, since those who don’t consume milk can sometimes have low iodine intake. It really depends on where you live (or where your food comes from) since the amount in fruits and vegetables varies according to where they are grown.

The most consistent and reliable sources of iodine are milk (often held in tanks that are cleaned with an iodine solution) and seafood. Sea vegetables are one good source of iodine in vegan diets, although the amount varies greatly and some types may contribute excessive amounts of iodine. The most reliable source of this nutrient is iodized salt—or an iodine supplement. The recommended intake for iodine is 150 micrograms per day for adults, an amount that is included in many multivitamin tablets.

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4 Responses to Soyfoods, Iodine and Thyroid Function in Vegans

  1. opiate addiction help December 4, 2010 at 2:37 pm #

    Really good writing! love your post. You are doing awesome work.

  2. Anna November 12, 2011 at 11:35 am #

    If you’re looking for blog fodder I’d love your take on this:

    I was especially perplexed by the part that mentioned a prison system that was serving 100 grams of soy protein a day (per person, I assume). I don’t know what other protein sources they’re using, but assuming it’s not 100% soy-based that means they’re serving more than 100 grams of protein per day, which seems high to me. But I’ve heard conflicting information on how much protein is actually necessary.

  3. LcoyoteS December 19, 2011 at 8:28 am #

    Hi Ginny,

    A recent blood test seemed to confirm that my thyroid is functioning normally, but I’m not convinced. I’m cold most of the time, even in the summer. I don’t have a lot of energy and I have been chronically depressed since childhood. I also have a family history of hypothyroidism on my mother’s side.

    I’m not sure what to do about this problem. I keep hearing over and over again that the only really effective treatment for thyroid problems is desiccated thyroid hormone. Naturally, this would not be an option for me even if my doctor agreed to do something about my complaints. Do you know of any vegan-friendly options for someone in my position?

    I have not tried taking vitamins or supplements of any kind, since they are so expensive and my family is always struggling to make ends meet.


  4. Liz October 18, 2013 at 10:07 am #

    I am newly vegan and I have Hashimoto’s Thyroiditis. I was wondering if consuming large amounts of soy is ok for this condition as long as I get enough iodine. Soy seems to be the best vegan protein source out there, so I am hoping I can eat it without issue as long as I have enough iodine.

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