Soyfoods, Iodine and Thyroid Function in Vegans

Soyfoods, Iodine and Thyroid Function in Vegans

By | 2008-02-21T14:06:00+00:00 February 21st, 2008|Tags: , |8 Comments

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.


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

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

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

    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 - Reply

    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 - Reply

    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.

  5. AmberSP June 5, 2016 at 11:18 am - Reply

    I found out about you through the Unnatural Vegan on Youtube. She promotes yourself and Jack Norris as reliable sources for diet and nutrition advise. I love all the foods containing goitrogens(i.e. tofu, cabbage, broccoli) is the asian stir frying method of cooking enough heat to destroy/convert/attenuate the goitrogens? I am curious to ask because I have a thyroid condition: take meds, exercise and have been avoiding favorites in fear of negative outcomes.

  6. Sheena August 3, 2016 at 12:59 am - Reply

    Hi, I’ve been vegan for about 10 months and I’m having some problems with fatigue etc. It might possibly be iodine? I’m taking B12, am pretty careful to eat iron-rich meals, and take an iron tablet occasionally. On the other hand I do eat a lot of soy. I’m in Ireland and the salt isn’t iodised, so I thought I’d use seaweed. I got dillisk – I was thinking kombu might give me too much? When I looked it up it said dillisk has 150-550 ppm of iodine. So should I aim for about 1g of dillisk a day? This is how I worked it out:

    The European Union has set a recommended daily allowance for adults of 150 µg iodine, with a maximum of 600 µg per day.
    Dillisk – 150ppm – 550ppm
    Bag of Dillisk is 28g, so it contains between 4200 µg – 15400 µg Iodine
    To get 150 µg: Between 1g (if 150ppm) and 0.27g (if 550ppm)
    Maximum to avoid going over 600 µg: 4g if 150ppm; 1g if 550 ppm
    – Aim for 1g?

  7. Vee July 23, 2017 at 1:24 am - Reply

    What are the dangers of excess iodine? A friend wants to take upwards of 5,000 to 10,000 mcg of iodine because she says that’s what the average Japanese person consumes. And most of them seem pretty healthy.

    • Ginny Messina July 28, 2017 at 5:58 pm - Reply

      No, that’s not what the average person in Japan consumes. There have been some cases where Japanese people have had very high intakes and they have developed thyroid problems. Too much iodine is very dangerous, so you should stick with the RDA which is 150 micrograms per day. And you’re already getting some of that from foods you eat.

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