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Iodine on a plant based diet: what the doctors say
Iodine on a plant based diet: what McDougall, Barnard, Goldhamer and Rogers say about seaweed, iodized salt and pills, with sources.
Updated . For education only, not medical advice.
Our view
Iodine is a mineral, so plants do not make it; they take up whatever the soil holds, and McDougall notes that crops grow without it, which is how a whole region can come up short12. A century ago the land around the Great Lakes was known as the goiter belt for that reason, an example McDougall, Novick and Rogers all bring up134.
Fewer doctors on this site speak about iodine than about B12 or vitamin D, and those who do split on how much it should worry a plant based eater56. McDougall, Rogers and Novick think food shipped from many regions now makes a shortfall unlikely, while Barnard warns that people who skip iodized salt and never eat sea vegetables may run low5738.
We give most weight to the low-fat clinicians, and their common ground is practical: have a known source, whether a little seaweed, iodized salt or, if needed, a supplement9610. On kelp we lean to the caution of Novick and Rogers, who point out that it can carry far more iodine than a person needs1112.
Where they agree
All of them treat iodine as a soil and sea mineral: McDougall and Novick describe inland soils poor in it, and Lisle links coastal living, with its fish and sea vegetables, to plenty of iodine and inland living to goiter1313. Barnard explains why it matters: the thyroid gland needs iodine to make its hormone6.
They also agree that the sea is where iodine is concentrated; Barnard names wakame and nori, Goldhamer names nori and kelp, and Novick warns about kelp and kombu precisely because their levels run so high61411. Barnard and Rogers both mention iodized salt as a simple source64, and Barnard adds that sea salt, Himalayan salt and kosher salt carry no added iodine unless the label says so8.
Where they differ
The doctors differ on how likely a shortfall is, which sea vegetables are safe, whether salt matters and whether a pill is ever the right answer515816.
How common a shortfall is
McDougall argued in 2015, and again in 2022, that people in modern countries eat produce from many places, so a food grown in poor soil is offset by the next one52. Novick said much the same in 2009, and Rogers called low iodine fairly uncommon in 2024310. Barnard sees more risk: in 2020 he said someone raised far from the sea who rarely eats seaweed may get a little low6. Goldhamer sits between them, saying in 2025 that a varied diet grown in soils with enough iodine generally covers it16.
Which sea vegetables
Goldhamer’s center serves a sea vegetable like nori weekly, and in 2025 he named nori and kelp as very rich sources914. Barnard pointed in 2025 to the nori on sushi and the wakame in miso soup17. Novick, writing in 2012, saw nori as low in iodine and advised against kelp and kombu, which concentrate it from seawater, and against hijiki for its arsenic1115. Rogers is the most wary: in 2022 he warned that seaweeds sold for iodine may carry contaminants, and in 2024 he said kelp can hold enough iodine to push the thyroid too far, and that he is nervous about algae because of a natural toxin1812.
Salt
Barnard credits iodized salt, sold from around 1925, with ending deficiency in the US almost at once, and worries that people now cutting sodium or buying specialty salts lose that source8. Rogers, who avoids salt, said in 2024 that iodine has never been a problem for him, and listed leafy greens, carrots, oats and green peas among plant sources7. When he does mention iodized salt, he asks people to choose one without aluminum as an anti-caking agent410.
Pills or food
Barnard put the need at 150 micrograms a day and in 2020 suggested iodine as a third supplement for people who get neither sea vegetables nor iodized salt6; in 2023 he noted that health food stores sell iodine pills usually made from kelp or other seaweed19. Goldhamer said in 2025 that routine iodine pills should not be needed and that plant sources are, in his view, better than a supplement1416.
What each expert says
JMJohn McDougall
McDougall counts iodine among the few minerals that can truly be lacking, because it depends on soil, and he recalls the Great Lakes goiter belt and rural parts of Africa where iodine is still supplemented1. He reasons that in modern countries food arrives from many regions, so one poor soil is made up by the next, naming corn from Idaho and apples from Washington5. He returned to the goiter belt in a 2022 talk on supplements2.
Barnard names seaweed and iodized salt as the main sources and warns that many people now get neither68. He says the iodine in cow’s milk comes largely from iodine disinfectant on the udder and from supplements fed to the cows20. He gives 150 micrograms a day as the need, from kelp based pills or seaweed itself19.
Goldhamer’s 2022 outline of a healthy day includes a sea vegetable such as nori once a week to cover iodine9. In 2025 he said sea vegetables are rich enough that routine supplements should not be needed, and that he prefers plant sources to a pill1416.
Rogers sees iodine as a small issue for vegans now that food comes from many places47. He suggests iodized salt free of aluminum for anyone concerned, but avoids salt himself and keeps away from kelp and other algae1012.
Writing about seaweed in 2012, Novick advised against kelp and kombu for their very high iodine, while describing nori as low in both iodine and sodium1115. In 2009 he used the old goiter belt as his example of a soil short in a mineral, but rated the present-day risk as slight3.
Speaking in 2021 about how early humans spread, Lisle noted that groups living along the coast would have eaten fish and sea vegetables rich in iodine, while those who moved inland could end up with goiter13.
On a fully plant based diet, we make sure iodine has a known source, as these doctors discuss: a modest amount of sea vegetables, iodized salt or a supplement96. We stay away from kelp and other very high iodine seaweeds, following Novick and Rogers1112. Which source suits you, and whether you need a pill at all, are questions for your own doctor, especially before pregnancy or with a thyroid condition. This page is education, not medical advice.
Each small number links to its reference below: the video at the exact second, or the page where it was said.