The Benefits of Seaweed (And When To Avoid It)

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The benefits of seaweed and how to use it in recipes
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Most of us are familiar with seaweed in our sushi, and the accompanying miso soup. But beyond the delicious taste, have you ever wondered about the health benefits of seaweed?

Incredibly rich in antioxidants, vitamins, and minerals, seaweed packs a serious nutritional punch.

What Is Seaweed?

Seaweed, or algae, belongs to a group of plant-like organisms that grow in the sea.

Some algae are one-celled organisms such as microalgae, which means that they are more like bacteria that also generate energy through photosynthesis.

Most of the seaweed that we consume as food have many cells. Seaweed is part of a healthy diet and is used in herbal medicines in many traditional cultures.

What Are the Different Types of Seaweed?

Scientists have categorized types of seaweed into different categories based on their pigments, cell structure, and other traits. The groups (or phyta) of seaweed that are commonly consumed include:

How to Cook and Eat Seaweed

If you live near an Asian market or Chinatown, you may be able to find fresh seaweed. Otherwise, you may find many types of dried seaweeds in the supermarket and online, such as on Amazon.

Dried seaweed would need to be soaked in hot water, and rinsed well before use. Some thicker and tougher seaweed like kombu might be better sliced thin or boiled.

Seaweeds are very versatile. Here are a few different ways to enjoy them:

  • Snacking out of a bag – Nori and dulse can just be eaten out of a bag. You will want to check the labels and watch out for some brands of snacking nori that contain a lot of MSG though. Seasnax is a good brand for this that uses seaweed from Korea and clean ingredients.
  • Salads – Most types of seaweed can be made into a Japanese-style salad with vinegar, sesame oil, ginger, and garlic. Try this recipe.
  • Soups – Seaweed tastes delicious in bone broth, which makes it seaweed soup.
  • Sprinkled on other foods – Seaweed flakes can be sprinkled on salads, rice, soups, or any other dishes.

Most seaweed is not bitter. Some types are a bit sweet and may even have umami flavors, which means that it may be easier to get some picky eaters to eat seaweed than vegetables.

Benefits of Seaweed

The unique properties of seaweed make it beneficial to the body in several ways. Here are a few seaweed benefits:

Vitamins and Minerals

Seaweed is much more nutrient dense than any land vegetables. It is an excellent source of micronutrients including folate, calcium, magnesium, zinc, iron, and selenium. More importantly, seaweed is a great source of iodine.

DHA and EPA omega-3 fatty acids

Unlike land plants, seaweed contains preformed omega-3 fatty acids DHA and EPA, so seaweed or algae oil can be a reliable source of omega-3 for vegetarians.

Aids with Digestion

Beans can cause gas and stomach upset for many people. This can be easily fixed by adding kombu, a particular kind of seaweed, to the beans when cooking.


Seaweed contains many antioxidants. As part of a healthy diet, seaweed can help protect against oxidative stresses and prevent chronic diseases such as cancer and digestive problems.

Fiber and Prebiotics

All plants contain fiber, but seaweed also has other odd types of carbohydrates that we lack the digestive enzymes to digest. These include  carrageenan, fucan, galactan, and many more. These carbohydrates then become foods for the bacteria (see this study for a more detailed explanation).

What you eat directly influences which bacteria dominates in your gut. The types of bacteria that can feed best on the foods you choose to eat will grow better (read more on this fascinating topic here). This explains why some cultures handle different types of food better than others. In fact, scientists found that the gut bacteria in healthy Japanese people are higher in bacteria that can digest the types of carbohydrates in seaweed (source).

Potential Risks from Eating Seaweed

There are a couple potential concerns to be aware of when consuming seaweed:

Too Much Iodine Can Cause Thyroid Problems

Iodine is a very important mineral for thyroid functions, and seaweed is a great source of iodine. While the thyroid can adjust to higher intakes of iodine, it is possible to develop thyroid problems from too much iodine. This may be especially true if you are susceptible to thyroid issues (like me).

A Japanese study found that women who regularly consumed 15 – 30 grams of kombu had elevated TSH, and reduced free T3 and T4. When these women stopped consuming seaweed, then their TSH and thyroid hormone levels returned to normal. Therefore, the authors of this study recommended not to exceed 3 mg of iodine (a serving of seaweed typically contains 20 – 50 mg).

Asian cuisines typically serve seaweed along with foods that contain goitrogens that inhibit iodine absorption by the thyroid. These include the common Asian staples such as tofu, soy milk, and cruciferous vegetables. This might explain why most Japanese and other Asian people can consume seaweed without any problem (source).

Those with existing thyroid disease (or those predisposed to it) should monitor total iodine intake. This is especially important for those who live in countries that fortify foods and table salts with iodine. Generally, consumption of seaweed on occasion (2 – 3 times a week) as a condiment (1 – 2 tablespoons) generally will not exceed the 3 mg limit of iodine.

To be safe, monitor thyroid hormone levels with your doctor as you introduce seaweed into your diet to see if eating seaweed will possibly cause a thyroid problem for you.

Digestive Problems from Seaweed Carbohydrates and Fibers

Seaweed contains many types of carbohydrates our digestive system can’t digest. These carbohydrates are passed down to our gut bacteria. For people prone to digestive problems or with small intestinal bacterial overgrowth, these carbohydrates cause significant issues.

The food industry widely uses these carbohydrates, such as carrageenan and agar, to stabilize or texturize foods in the food industry. Carrageenan, in particular, is very problematic. It causes inflammation both in the gut and throughout the human body. It is therefore very wise to avoid carrageenan as a food additive.

While pure carrageenan has been linked to health problems, there is no study linking carrageenan in whole food sources to the same problems that have been linked to carrageenan in isolation. It is perhaps best to avoid seaweeds that are higher in carrageenan content such as Irish moss and occasionally enjoy other seaweeds in moderation.

Radioactive Levels from Fukushima Radiation

A high iodine diet can protect against radioactivity. This is why when the Fukushima nuclear plant melted down, the Japanese government gave iodine supplements to aid workers and evacuees.

Chris Kresser discusses the topic of Fukushima radiation in Pacific seafood in this blog post. He states that the levels of radiation in the US Pacific coast are rather insignificant when compared to other background sources of radiation that already exist in the US, or compared to our exposure flying on an airplane. Bottom-feeding fish near the coasts of Japan show more contamination, but even then the levels of radioactivity fall below the international dose limit.

In fact, Maine Coast, a seaweed purveyor that regularly tests their products for toxins, found that their products only have background levels of radioactivity even right after the Fukushima event in March 2011 (source).

Because seaweed is at the bottom of the food chain (where it is eaten by other animals), the concentration of toxins in seaweed is much less than in fish or other animals that eat the seaweed.

Toxic Heavy Metals

While rich in beneficial minerals, seaweed also can contain toxic metals. This likely depends on the type of the seaweed, where it is harvested from, and the variation of toxin levels in the water. Several reports detail the heavy metal content of seaweed:

  • Heavy metals in laver, seatangle, sea mustard, hijiki, and gulfweed from the South Korea coast are below safety limits (source, and source).
  • Hijiki, regardless of brand, contains arsenic that is above the safety limit (source).
  • A Spanish study extensively compared various types of seaweed imported from Japan, China, Korea, and Chile that are sold in Spain. They concluded that most seaweed products are safe with respect to WHO guidelines. However, some species such as Hijiki and H. fusiforme may be high in arsenic (source).

Heavy metals levels in seaweed can really vary from batch to batch. The best way to know for sure is to purchase your seaweed from companies that regularly third-party lab test their products for heavy metal levels. One company I like that does this is Maine Coast. They publish their test results on their website here.

Remember that heavy metal exposure also comes through other sources like the environment and foods like fish and seafood. Everyone’s ability to remove these heavy metals from their bodies differs. If you are concerned about heavy metal levels, it might be wise to avoid seaweed and seafood altogether.

Seaweed as a Superfood: How It Stacks Up

  • There are many benefits of seaweed and it is a very nutritious food.
  • Healthy people can enjoy seaweed as a condiment a few times a week.
  • If you have concerns about thyroid health or digestive function, you may want to speak to your doctor about monitoring your condition as you introduce more seaweed into your diet.
  • With a few exceptions, radioactivity and heavy metal toxicity is of low concern for seaweed.
  • In general, seaweed harvested from the Korean coast is quite safe.

When in doubt, purchase your seaweed from a reputable company that tests their products for contamination, such as Maine Coast.WM-Seaweed-InfoGraph

What is your experience with seaweed? Do you have any concerns about its safety? Please share in the comments below.

Katie Wells Avatar

About Katie Wells

Katie Wells, CTNC, MCHC, Founder of Wellness Mama and Co-founder of Wellnesse, has a background in research, journalism, and nutrition. As a mom of six, she turned to research and took health into her own hands to find answers to her health problems. is the culmination of her thousands of hours of research and all posts are medically reviewed and verified by the Wellness Mama research team. Katie is also the author of the bestselling books The Wellness Mama Cookbook and The Wellness Mama 5-Step Lifestyle Detox.


31 responses to “The Benefits of Seaweed (And When To Avoid It)”

  1. Laura Avatar

    I like much of what you do but please stop citing Chris Kresser. He is a fraud with zero medical credentials and cherry picks science to suit his agenda.

    1. Katie Wells Avatar

      I’m sorry you’re not a fan of his but I fundamentally disagree with you. He’s been a guest on the podcast several times and is one of the smartest people in the natural health space today…

  2. Scott Avatar

    Marine microalgae do have the essential omega 3s, EPA and DHA. However, macroalgae, the seaweeds we eat such as Nori and those used in salads and soups do not have them. It’s an important distinction. We rarely encounter microalgae in our diets.

  3. rachel Avatar

    Hi, thanks for the information. I have been consuming seaweeds for many years. The information I have seen is that because of the iodine in it, it is helpful for women, and helps with preventing cancer. Many years ago soils were much healthier and contained iodine for the plants (and animals). I like putting kombu or wakame in soups or stews, but I also like eating nori (eating too much can lower B12 levels) and dulse (my mom grew up in Maine and remembers eating it as a child). I gave powdered organic kelp to my doggies 2x weekly as a supplement. Seaweed is also nice to add to miso soup.

  4. Joe Avatar

    Ate about 2 cups of seaweed salad yesterday. Today I feel bloated and very uncomfortable like I would feel better if I could vomit or go to the bathroom but I’m having trouble with both. Hot and cold spells like typical food poisoning except usually I can vomit or pass it through without much effort. Sweating in the fetal position on my bathroom floor.

  5. Teresa M Avatar

    Hi Katie

    Having grown up with eating seaweed, it’s fantastic to hear the benefits from consuming it. We would always have it in our soups and the occasional spring roll!
    However, it’s quite alarming to hear the high levels of toxic metals found in them and I appreciate you highlighting this in your thorough and informative article.


  6. Jessica Sequinot Avatar
    Jessica Sequinot

    After seeing reports of plastics in sea salt. I’m wondering if the same applies to seaweed. My son eats two packages of these snacks a day.

  7. Charla Avatar

    You say, “Too Much Iodine Can Cause Thyroid Problems”. I run an iodine group with several thousand members. The ONLY time I have ever heard of iodine causing problems is if someone has autonomous thyroid nodules or if they are not also using selenium, which is critical to absorption of iodine in the body. There are people using information from Dr. David Brownstein, MD and Dr. Jorge Flechas, MD, MPH who have taken hundreds of milligrams a day of Lugol’s iodine, which is a combination of potassium iodide and iodine. I recommend this lecture by Dr. Flechas to other MDs regarding total body iodine sufficiency. There is a protocol recommended by several groups that has specific recommendations of safe use of iodine and excretion of bromine, which blocks iodine absorption.

  8. Mary DeGrezia Avatar
    Mary DeGrezia

    Thank you for providing concise yet thorough info on seaweed!

  9. June Avatar

    Hi, I read the article about fish and fukushima radioactive contamination and was so happy to read I don’t have to worry about cold water fish anymore. However, the article was written in 2013 4 years ago which makes me wonder if there have been any changes because, Japan cannot stop the radioactive leak into the Pacific Ocean it’s been spilling into the ocean since the breach???

  10. Debra Avatar

    I was wondering about the radiation in the seaweed from Japan. Even though it is organic, there is still radiation from Fukushima. do you eat this seaweed?

  11. Diane Avatar

    I have been eating roasted seaweed for 3 months. Funny, I just noticed in the last couple of weeks how fast my hair is growing and curly now. Is this too much iodine affecting my thyroid.
    I was eating quite a lot. The whole plastic tin it comes in.

    1. Gail Smith Avatar
      Gail Smith

      I loved those snacks (I just learned from another article with pictures that those little thin strips in the plastic case) are called Nori. I was eating 1-2 of those little packages per day for a while — probably a bit much. I bought them from an international grocer in my area. I did become concerned about where they were being sourced from – cleanliness, nutritional content. I took a break from eating them after months eating them at that pace.

  12. Carol Jean Avatar
    Carol Jean

    Seaweed is so delicious!! Have any of you tried the seaweed-infused pastas by Blue Evolution? They grow sustainable seaweed in North America while most of the seaweed we eat is imported.

  13. Tina T Avatar

    I love seaweed! However, I have noticed when I do eat it (the packs of dried seaweed) I sweat profusely !!! Every time ! Why???

  14. Patra Avatar

    No, you cannot eat seaweed. Consult with your doctor. I come from the medical field, according to medical reports, seaweed can increase your chances of inducing new cancer cells. This is not a medical website, please consult your doctor or medical provider. They will be the only one(s) with the answer. Also, if you’re taking synthroid or levethyroxine, you don’t need to take seaweed, as it will only increase the hormone production in your body. If you’re taking any of these they are the replacement for iodine. However, some people prefer to go with the alternative however, since you had cancer you really need to consult your doctor. Hope this helps.

    1. Marian B. Avatar

      Patra, without ignoring your opinion, the Asian cuisine of Japan is using seaweed for a long time now. I’ve eaten seaweed for at least 45 years, which is the number of years of my career as holistic healthcoach and nutritionist. I mainly cooking kombu with rice or pulses, to improve digestion of the latter and to add minerals to my diet, which is vegetarian in summer, with a tiny amount of meat in winter. Seaweed is a great mineral source as well, for vegetarians and veganists.

      There’s no evidence that I can find, that says that seaweed causes the growth of cancer cells. Unless it’s seaweed harvested near Fukushima. But also in that case, it’s not the seaweed but the nuclear disaster in that area that contaminates the seaweed growing offshore.

      Here’s an article, stating the opposite of what you’ve presented as your opinion:

      Seaweed is helpful in a detox of heavy metals, many people who are aware of the heavy metals present in fish and in the air we breathe after chemtrailing occurs in our skies., take Chlorella tablets.
      And to this day I’m healthy as a fish… uhhh… a fish in a mountain lake 😉

  15. Carmen Avatar

    Can I eat seaweed if my thyroid has been removed due to cancer? Thank you!

    1. Wellness Mama Avatar

      I would just start with very small servings and see how you feel afterward and work your way up to the recommended amount.

  16. Brenda Avatar

    From your article, it looks like seaweed consumption can correlate w/hypothyroidism. Do you know of any concern with eating too much seaweed for people w/hyperthyroidism? Might it be helpful? Thank you for your helpful and conscientious blog.

  17. Ashley DeBoer Avatar
    Ashley DeBoer

    Love all your blog posts and your podcast. I have learned so much!

    Are you familiar with the seaweed snacks at Trader Joes? I have been eating these and they are non gmo but there is not much else I can find about them. Thank you!

  18. June Avatar

    Omgosh, you really did your research (as always) on seaweed thank you! It’s awesome info. My husband has ic intercystle cystisis and hoshimotos disease, we were just going to ad seaweed to his diet to help his ic without alot of research?

    Thank you so much for everything you do, I love your blog and have for many years, you are truly a blessing! J

  19. Petra Avatar

    Perfect timing of this article since I just bought some kelp capsules yesterday. Each has 30 mg of it, I bought it to supplement my lack of iodine. But I didn’t realize that just a few leaves of wakame in my soup is just as good. Will be returning the pills, I’ve never had thyroid problems, and if consuming to much can be an issue I would prefer not to put my health at risk.

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