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Seaweed: The Ocean's Answer to Vegan Nutrition (And Sushi Withdrawal)

  • Writer: Emanuele Bortolotto
    Emanuele Bortolotto
  • Jul 26
  • 7 min read

Updated: Sep 7

Staring out at the water, gets a person thinking about the strange and ancient things that live down there in the murky depths. Creatures with too many tentacles, fish with their own built-in lanterns, and, of course, the vast, swaying forests of seaweed.

For most of my life, I thought of seaweed as either a slimy, unpleasant thing that touches your leg at the beach, making you panic and run out of the water like you've been electrocuted, or as the weird, black paper that stops your sushi from falling apart. It’s a food that exists on the fringes of the Western palate, a deeply misunderstood ocean vegetable.

But in my investigations into the world of nutrition, particularly vegan nutrition, I kept stumbling upon it. It was mentioned in hushed, reverent tones, spoken of as a "superfood," a "mineral powerhouse," and the secret key to a healthy plant-based diet. I realized I had been overlooking a whole kingdom of food. So I decided to launch a full-scale investigation into the slimy, salty, and surprisingly crucial world of marine algae. 🌊


A Field Guide to the Ocean's Garden: What Is Seaweed, Anyway?


The first thing I discovered is that "seaweed" isn't really one thing. It’s a broad, catch-all term for thousands of different species of marine algae. And algae, I learned, are not technically plants in the same way a carrot or a potato is a plant. They are a more primitive life form, a sort of watery plant that got so good at floating about that it never bothered to invent roots, stems, or flowers.

I was watching my editor, try to eat a piece of sushi for the first time. It was a deeply uncoordinated and slightly tragic affair involving a lot of dropped rice, but it got me thinking about the seaweed wrapping, the nori. It's the unsung hero, the edible, salty envelope holding the whole chaotic project together. And it turns out, that edible envelope has a lot of interesting relatives. For culinary purposes, we can group them into a few main families.


Nori (The Crispy, Salty Gateway Seaweed)


This is the one you already know. Nori is a type of red algae that is shredded, pressed into thin sheets, and dried, a process that looks surprisingly like traditional paper-making. It’s the crispy, slightly sweet, and deeply savory wrapper used for sushi rolls (maki) and onigiri. It’s also often sold in toasted, snack-sized sheets, which are a genuinely addictive, if slightly weird, alternative to crisps. 🍣


Kombu (The Leathery Umami Blanket)


Kombu is a type of kelp, a brown algae that grows in vast underwater forests. It’s sold in thick, dried, leathery strips that are often covered in a fine white powder. This powder is not mold; it is pure, crystalline glutamate, the source of the umami flavor. Kombu is not usually eaten directly. Its primary purpose is to be the star ingredient in dashi, the foundational savory broth of Japanese cuisine. A single strip of kombu, steeped in hot water, creates a broth with a profound, complex, and deeply satisfying savory flavor. It is an umami bomb. 💣


Wakame (The Silky, Tender Soup Friend)


If you’ve ever had miso soup or a bright green Japanese seaweed salad, you’ve eaten wakame. It’s another type of kelp, usually sold in dried, shriveled, dark green pieces. When you rehydrate it in water, it unfurls and expands into beautiful, silky, tender, slightly sweet ribbons. Its delicate texture and flavor make it a wonderful addition to soups, salads, and noodle dishes.


Dulse (The Confusing Sea Bacon)


Dulse is a red algae with a soft, chewy texture and a unique, smoky, and savory flavor. When it’s pan-fried until crisp, it develops a flavor that is uncannily similar to bacon. I know, it sounds like a lie vegans tell themselves, but my investigation confirms it to be surprisingly true. Dulse flakes are also a fantastic salty, savory seasoning to sprinkle on... well, anything.


The Nutritional Treasure Chest: Unpacking the Minerals 💎


So, why should anyone bother eating this stuff? Because, as my investigation revealed, seaweed is one of the most nutrient-dense foods on the planet. It is literally soaking in a mineral-rich broth—the ocean—its entire life.


Iodine: The Main Character


This is the number one reason seaweed is so critical for a well-planned vegan diet. Iodine is a mineral that is absolutely essential for the healthy function of your thyroid gland. Your thyroid is the master regulator of your metabolism, and it produces its crucial hormones by pulling iodine from your blood.

An iodine deficiency can lead to hypothyroidism (an underactive thyroid), which can cause fatigue, weight gain, and depression. In severe cases, it can cause a goiter, a visible and sometimes massive swelling of the thyroid gland in the neck.

The problem is that the amount of iodine in land-based plants is entirely dependent on the soil they were grown in, and much of the world's soil is iodine-poor. The most reliable sources in a standard diet are seafood and dairy (because of iodine-fortified feed and sanitizing solutions). Without these, a vegan is at a very high risk of deficiency.

Seaweed, however, is the most potent source of iodine on the planet. But this is both a blessing and a curse.

Seaweed Type

Average Iodine Content (per gram)

Notes

Kombu (Kelp)

~2500 mcg

🤯 Extremely High! Use with caution.

Wakame

~140 mcg

A very good, strong source.

Nori

~35 mcg

A great, safe, daily source.

Dulse

~70 mcg

A good, moderate source.

The recommended daily intake of iodine for an adult is 150 mcg, with an upper tolerable limit of around 1,100 mcg. As you can see from the chart, a single gram of kombu can contain over 16 times your daily need. While a small amount is good, eating too much kelp too often can lead to iodine toxicity, which can paradoxically also cause thyroid problems. Nori, on the other hand, is a much safer bet for regular consumption.


The Supporting Cast: Calcium, Iron, and Magnesium


Beyond iodine, seaweeds are a good source of a whole host of other minerals. They can be a significant source of calcium, especially for those who don't consume dairy. They also contain a decent amount of iron, and they are packed with magnesium, a mineral that is crucial for muscle function and relaxation.


The B12 Myth: A Crucial Public Service Announcement 🚨


During my investigation, I came across one of the most persistent and dangerous myths in the world of vegan nutrition: the idea that seaweed is a reliable source of Vitamin B12.

This is categorically false. Let me be as clear as humanly possible about this.

My research shows that while some seaweeds, particularly nori, do contain a substance that is chemically identified as B12, it is primarily a B12 analogue. An analogue is like a key that has been poorly copied. It looks almost identical to the real key. It can fit into the keyhole (your body's B12 receptors), but it cannot turn the lock. It is an inactive, useless form of the vitamin.

Even worse, by getting stuck in the lock, this fake B12 analogue can actually block the real, active B12 (from a supplement or fortified food) from getting in. So, relying on seaweed for B12 is not just ineffective; it could actually be counterproductive and make a deficiency worse. Please, I implore you, do not believe this myth. It is dangerous. Vegans must get their B12 from supplements or reliably fortified foods.



Questions from the Internet: "Okay, so which seaweed is the absolute healthiest?"


This is like asking which tool is the best in a toolbox. It depends on the job you need to do.

  • For a massive, therapeutic dose of Iodine: A small piece of Kombu used in a broth is the most potent.

  • For a safe, daily source of Iodine and other minerals: Nori is the undisputed champion. A couple of sheets a day is a fantastic nutritional habit.

  • For use in soups and salads: Wakame is the best for texture and flavor.

  • For a protein and antioxidant boost in a smoothie: Spirulina (a microalgae) has the highest protein content.

    My final verdict is that a truly healthy diet would include a small amount of a variety of these different seaweeds to get the full spectrum of benefits.


Questions from the Internet: "Can you eat too much seaweed?"


Yes, absolutely. As my investigation showed, the primary risk is iodine toxicity from brown algae like kombu and other forms of kelp. Eating a large bowl of kelp noodle soup every day is a very bad idea. The secondary risk is the potential for contamination with heavy metals, like arsenic, as seaweed can absorb these from polluted waters. The key is moderation. A few sheets of nori a day, a weekly bowl of miso soup with wakame, and using kombu occasionally to make broth is a perfectly safe and healthy approach.


Internal Link Break!


The number one reason to incorporate seaweed into your diet is to ensure you're getting enough iodine, a mineral your thyroid gland desperately needs to function. If you're wondering what happens when your thyroid gets angry due to a lack of this crucial nutrient, I've investigated that very topic right here: [Do Vegans Get Enough Iodine, or Is My Thyroid Quietly Plotting Revenge?]


The Conclusion: Embrace the Ocean's Garden


So, after my deep, and at times surprisingly slimy, investigation, what have I learned about seaweed?

I’ve learned that it is an ancient, incredibly diverse, and nutritionally potent food group that most of us in the West have been foolishly ignoring. For those on a plant-based diet, it is not just a novelty; it is an essential tool, the most reliable plant-based source of the critical mineral iodine on the planet.

But it is not a magic bullet. It comes with serious caveats. The risk of iodine overload from kelp is real, and the myth of it being a B12 source is dangerous. But approached with knowledge and respect, seaweed can be a powerful ally in your quest for health. It’s a taste of the wild, ancient, and mysterious world of the ocean, right there on your plate. So go forth, and embrace the weird and wonderful foods that the ocean's garden has to offer. 🌊

Seaweed is a fantastic source of umami, the savory fifth taste that makes food so satisfying.


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