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I have already asked the question on Quora in the past, yet I have not received satisfactory answers. See the link here.

I'd like to consume miso soup often, however, the dashi for the soup (Japanese broth, the basis of many Japanese soups and sauces) is made from boiled kombu seaweed, which is very high in iodine.

I have read that if one pre-soaks kombu in water it removes a lot of iodine, yet does not comprise the taste much, however I was not able to locate the daily recommended dose of dashi made from kombu, nor any other recommendations (e.g. use kombu 2x10 cm long, boil for 20 seconds - this will be approximately 60% of your iodine daily intake).

Also, the Japanese often eat tofu and other foods that contain several chemicals that suppress the high iodine intake, though, again, no real numbers.

Are there any real studies/numbers on this? Of course, the iodine concentration in such broth strongly depends on the kombu used, the length of boiling etc., yet I believe there must be some average values one can take into consideration in order to maintain thyroid health.

  • I think the variations you mention in the last paragraph make study virtually impossible. You also seem to be treating a food as if it were a medication with profit potential. Who would fund such studies and why? – Carey Gregory Jan 22 '18 at 19:47
  • @CareyGregory Thank you for your comment! (I am unsure how I used food as a medication with profit potential?) I believed there had to be some studies since virtually everyone in Japan consumes foods with high iodine content. Hence I believed that there sure was a way how to establish safety measures (use this amount of kombu and boil for this long, eat 400 ml max a day). Maybe I was mistaken? – Fipah Jan 22 '18 at 23:08
  • I'm sure iodine levels have been studied in Japan, but I doubt it's been studied in the way you're looking for. I could be wrong, of course, but it's very hard to quantify the things you're looking for, so such a study would be very difficult. Who would fund it? – Carey Gregory Jan 22 '18 at 23:26
  • Sure, hence you'd say there is no way of telling how much iodine can one consume from typical Japanese foods a day? – Fipah Jan 23 '18 at 11:15
  • I really think google is your friend on a topic like this...but here is something to get you started: ncbi.nlm.nih.gov/pmc/articles/PMC3204293 – user12676 Jan 23 '18 at 12:51
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This study from Australia https://www.mja.com.au/journal/2010/193/7/iodine-toxicity-soy-milk-and-seaweed-ingestion-associated-serious-thyroid indicates that iodine toxicity has been documented in people consuming soy milk made with kombu and illustrates the dangers of importing a foreign diet or manufactured food substance.

We report a series of cases of thyroid dysfunction in adults associated with ingestion of a brand of soy milk manufactured with kombu (seaweed), and a case of hypothyroidism in a neonate whose mother had been drinking this milk. We also report two cases of neonatal hypothyroidism linked to maternal ingestion of seaweed made into soup. These products were found to contain high levels of iodine. Despite increasing awareness of iodine deficiency, the potential for iodine toxicity, particularly from sources such as seaweed, is less well recognised.

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  • Thanks! I have seen that before, yet there are no kombu/dashi concentrations and recommendations, but thanks! – Fipah Feb 23 '18 at 14:02
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There are no studies looking at iodine concentrations of that specific soup broth that I could find. But this study, published in Nutrition Journal 2 years ago, looks at iodine intake in various Japanese dietary groups.

In one type of diet, participants consumed more than 1 bowl of miso soup and 2 servings of seaweed a day, and their daily iodine intake was about 650 micrograms, right in the middle of the recommended range of 150-1100 micrograms a day.

So you should be just fine eating plenty of miso soup and/or seaweed.

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  • Thank you! I have already read it, though some time ago, that is why I asked the question here, but I will recheck it, thank you! – Fipah Jan 23 '18 at 21:32
  • Many people are prone to be too low in iodine. The "(typical groups of) Japanese" part makes a less than ideal match to "you" without clarification. Not counting hereditary/genetics: esp the late/sudden introduction of high levels of iodine (in a diet) might necessitates more care, guidance, and monitoring of thyroid function. Kombu, nori etc might pack quite too much of a punch! If no analysis label is on the stuff intake should very probably be limited somewhat. A general 'clean' bill is ill advised. – LаngLаngС Feb 3 '18 at 4:47

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