Seaweed provides numerous nutritional health benefits. Packed with fiber, minerals, vitamins, and iodine, just to name a few, it’s no wonder these plants are considered the “leafy greens” of the sea. But did you know consuming too much seaweed could potentially be harmful to your health? Let’s explore.

I think we need to give our ocean plants a bit more love. And by ocean plants, I mean macroalgae.

First of all, these underwater ocean-dwelling plants are not only packed with health benefits but they also have the power to help draw out CO₂ from the atmosphere, reverse ocean acidification, ¹ and have the potential to be used as a renewable energy source ² (more on that in a future post). I could write an entire book on the various environmental benefits of seaweed but for the purpose of today’s post, I’m just gonna explore its health benefits, which are plenty.

1. What is seaweed?
2. Health Benefits:
   1. Iodine
   2. Fiber
   3. Vitamins & Minerals 
3. Health Risks?
4. The takeaway?
5. Recipes

But first, what is seaweed? 

“Seaweed,” according to the National Ocean Atmospheric Administration, “is the common name for countless species of marine plants and algae that grow in the ocean as well as in rivers, lakes, and other water bodies.” ³ 

There are thousands of different varieties of algae. In fact, it is estimated that the term algae includes anywhere from 30,000 to over 1 million different species.  ⁴

These species are divided into 4 main categories. Green algae, Brown algae, Red algae, and Blue-green algae. ⁵

And while this is a relatively new delicacy in American cuisine, cultures in Asia, Britain, and the Carribean have been consuming them for thousands of years. ⁶ And, it’s apparent they were on to something. These sea greens are chock full of minerals, vitamins, fiber, antioxidants, and iodine, just to name a few.

One of the reasons this plant is so nutritious is it easily absorbs sunlight and it’s also able to store minerals from the ocean, which is both good and bad. (More on that below). ⁷

Common edible seaweeds

If you’ve eaten Japanese, Korean, or Chinese cuisine at some point in your life, you’ve most likely encountered one or more of these types of sea vegetables.

– Wakame (Brown Algae) — is most commonly used in seaweed salads and miso soup. ⁸
– Kombu (Brown algae) — a cousin to wakame, kombu is a type of kelp with a strong flavor. It’s often used as a  key ingredient in the Japanese broth known as dashi. ⁹
– Nori (Red algae) — probably the most recognizable, this seaweed, which is most frequently sold as dried sheets, is used in sushi rolls.
– Spirulina & Chorella (blue-green algae) — these blue-green freshwater algae are most commonly sold in the form of powders or capsules. 

Fun fact: 

While we prefer to think of spirulina as a plant, this superfood is in all actuality simply “pond scum.”

In fact, “new understanding of its genetics, physiology and biochemical properties caused scientists to move it to the Bacteria kingdom and the Cyanobacteria phylum.  At first, it was classified in the genus Arthrospira, but later it was placed into the genus Spirulina. There are several species, but three — Spirulina platensis, Spirulina maxima, and Spirulina fusiformis — are studied extensively because of their high nutritional as well as potential therapeutic values, according to the study’s authors. ¹⁰

Health Benefits of Seaweed

Iodine

Seaweed is considered to be one of the most natural sources of iodine. ¹¹

What is iodine and why does it matter?

Iodine is a trace mineral your body needs in order to maintain proper function, more specifically to support your thyroid. For those of you who need a bit of a refresher, “The thyroid is a small gland located in the lower-front part of your neck. It’s responsible for helping to regulate many of the body’s processes, such as metabolism, energy generation, and mood.” ¹²

(Note: Trace minerals are minerals your body only requires in small amounts to function) ¹³

The recommended daily intake (RDI) of iodine is 150 mcg per day for most adults, which could easily be covered by small quantities of seaweed. (For women who are pregnant or nursing, the requirements are higher.)  ¹⁴

The iodine content of algae varies widely, but it may contain more than 4,500 micrograms, according to the Linus Pauling Institute. ¹⁵

Risk

Consuming too much iodine in your diet (400 micrograms or more a day)¹⁶ is harmful to your health, “linked to thyroid cancer and hyperthyroidism, which is when your thyroid produces too much hormone.” ¹⁷ 

But iodine deficiency is just as detrimental to your health. “Without enough iodine, you may start to experience symptoms like weight changes, fatigue, including goiter (enlarged thyroid gland) over time.” ¹⁸

As always, you should consult your doctor if you have any concerns before consuming seaweed –especially if you’re already predisposed to thyroid issues.

Fiber

Like most leafy greens, seaweed is very high in fiber, especially soluble fiber.  I’ve gone over the health benefits of both soluble and insoluble fiber here.

Dulse seaweed has more than 5 grams of mostly soluble fiber per 3.5 oz, and kombu contains more than 6 grams, almost all soluble.

What differentiates seaweed from most plant-based greens is that these sea vegetables contain “agar, carrageenans, and other polysaccharides that are not only good sources of fiber but can also act as prebiotics, which may be of benefit to the bacteria (microbiota) in the large intestine.” ¹⁹

Prebiotics are food ingredients that nourish probiotics. Typically, they are fibers and certain sugars that we don’t digest or absorb but that the bacteria in our intestines feed on, thereby stimulating their growth and activity. ²⁰

Good source of vitamins and minerals

There’s no doubt that adding a bit of seaweed to your diet not only adds a bit of flavor to your dish of preference but it’s a simple way of boosting your intake of vitamins and minerals.

Seaweed is a rich source of several vitamins, including vitamin A (in the form of carotenoids), vitamin C, vitamin D, vitamin E, and B vitamins. Similar to kale, seaweed contains high levels of vitamin K. (More on Vitamin K benefits here)

This “sea vegetable” is also a rich source of several minerals, including calcium, magnesium, potassium, copper, and iron ²¹

Flavonoids and Carotenoids

In addition to vitamins A, C, and E, seaweed boasts a wide variety of beneficial plant compounds, including flavonoids and carotenoids, both of which are shown to protect your body’s cells from free radical damage. ²²

What are flavonoids and carotenoids? 

Both flavonoids and carotenoids are phytonutrients, aka “plant chemicals” that can be found in the cell walls of a variety of plants. Because of their antioxidant and anti-inflammatory behaviors, it’s believed that diets rich in flavonoid/carotenoid-containing foods can aid in the prevention of certain types of cancers and cardiovascular diseases. ^{23 24}

Fun Fact: Flavonoids and carotenoids are responsible for the vivid colors in fruits and vegetables. Cartenoids are more commonly found in your orange fruits and veggies such as squash, carrots, grapefruits, oranges, and apricots. (source) ²⁵

Nori Seaweed

Health Risks?

As mentioned above, seaweed is able to easily absorb minerals, which provide numerous health benefits. Alternatively, they can also easily absorb toxins and damaging trace elements such as arsenic, lead, and cadmium from the ocean. As a result, you should be wary of where and how your seaweed was sourced and make sure it’s been tested for purity. Certified organic products, for instance, cannot contain heavy metals and other contaminants. ²⁶

While researching for this post, one of the things I personally concluded was that I would avoid the hijiki seaweed, which, among seaweeds,  has been shown to contain the highest level of arsenic.  According to Berkley wellness nutritionist Jeanine Barone, “to be on the extra cautious side, eat seaweed at most three times a week, and try to vary types or brands.” ²⁷

Tip: Most U.S.-based companies that harvest seaweed regularly test their seaweed for arsenic and other heavy metals, as well as bacteria, polychlorinated biphenyls, i.e. industrial products or chemicals (you can read more about PCBs here), pesticides, and radiation. Two such companies you might consider checking out are Rising Tide Sea Vegetables and Maine Coast Sea Vegetables. (source) ²⁸

So, the takeaway?

Seaweed is a great source of fiber, iodine, minerals, and vitamins, but, as with anything, a little goes a long way. Personally, I will continue cooking with seaweed but will do so sparingly (will include seaweed mainly as a side dish), especially considering this isn’t a “plant” that I was raised on.

“My fear is that people are going to take it as a superfood…and eat a lot of it,” says Nancy Oliveira, a senior nutritionist at Brigham and Women’s Faulkner Hospital in Massachusetts. “Eating bowls of seaweed every single day could be too much of these trace minerals.” ²⁹

Note: Seaweed does contain omega-3s (ALA (alpha-linolenic acid) and small amounts of DHA (docosahexaenoic acid)) and varying quantities, depending on the type of seaweed, of complete protein.  Red seaweed has the most, with up to 50 grams of protein per 3.5 ounces of nori. ³⁰ But, the digestibility of seaweed protein varies by type (researchers are still looking into this), so I didn’t go into much detail. ³¹

Do you cook with seaweed? 

Here are a few of my favorite seaweed recipes:

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6422 - Miso Soup with Seaweed and Kale

6420 - Miso Soup with Greens and Tofu

6416 - Wakame Cucumber Salad

 

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