The Health Benefits of Sea Vegetables (Seaweed)

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Sea vegetables, or seaweed, are nutrient-dense forms of algae that grow in saltwater. The marine vegetation grows along shorelines around the world, but is commonly used in Asian countries as food. If you’ve ever eaten sushi or had Japanese, Korean, or Chinese cuisine, you’ve likely had it.

Seaweed is very versatile and can be used as a wrap in sushi rolls (maki) and a main ingredient in soups and stews. Sea vegetables are also increasingly common supplements included in smoothies or multivitamin capsules. They’re chock full of nutrients, so you only need a little to get plenty of nutrition.

Sea vegetables pack a decent supply of protein, fiber, polyunsaturated fats, and a number of important vitamins and minerals that can aid in optimal functionality and health for the body. Sea vegetables are very easy for your body to break down, so they are a highly bioavailable and safe choice—albeit in small doses—for an added boost of nutrition.

Types of Seaweed

There are multiple types of edible seaweed, and they are either red, brown, or green. Red seaweed is the most abundant type of sea algae in the world, but brown and green seaweed types are used more often for food.

Some commonly eaten varieties include:

  • Wakame: Wakame may be the most versatile sea vegetable, and is used in miso soup and seaweed salad. It is dark green with a silky texture and has a very high nutritional value.
  • Kombu: This type is widely eaten in East Asia and is one of the three main ingredients in the Japanese soup stock “dashi.” It is greenish-brown seaweed, and it’s used to enhance flavors, season sushi rice, or enjoyed alone with soy sauce and mirin. The powdered form can also be used to brew kombucha.
  • Nori: Nori might be the most recognizable type of seaweed for most Americans. It’s typically used to wrap sushi rolls and as a garnish on soups, the most notable of which is ramen. It is a species of red algae that is shredded, then pressed into thin, dried sheets that end up looking very dark green or black.
  • Dulse: Dulse is a reddish-green sea vegetable that grows on the northern coasts of the Pacific and Atlantic Oceans, and researchers from Oregon State University have patented a strain they say tastes like bacon when fried. Currently, it’s sold dried, flaked, and in whole leaf or powdered form.
  • Arame: When soaked, this variety of seaweed looks like brown shoelaces and has a mild, slightly sweet flavor. It is usually added to edamame beans or stir-fried into Japanese soba noodles.
  • Hijiki: Often served as an appetizer at Japanese restaurants, it has been a part of the Japanese diet for centuries. It turns black after boiling, and is traditionally associated with myriad health benefits. Hijiki, like most seaweed, should not be consumed in high amounts. Although there are different reasons across the species, hijiki contains high levels of inorganic arsenic.

Seaweed Benefits

Small amounts of seaweed can contribute to your health in big ways. Let’s take a look at some of the biggest benefits it can have for your health.

1. Supports Thyroid Function

Seaweed is very high in iodine, which is essential for thyroid function and can be lacking in the American diet at times. It’s typically found in table salt in American households, but sea salt and other forms of salt that are not iodized have become increasingly common.

A healthy thyroid is needed to release hormones promoting growth, energy, and cell repair. Iodine is needed for optimal thyroid function.

Because of its unique growing environment, seaweed is one of the best sources of iodine on the planet. It absorbs iodine at a high rate, with varying levels between different seaweeds. For example, on average:

  • Kombu contains 2,524 micrograms (mcg) per gram.
  • Wakame contains 140 mcg per gram.
  • Nori contains 37 mcg per gram.

With the recommended daily intake of iodine being 150 mcg, kombu offers 1,682% RDI, with 93% for wakame and 25% for nori.

2. High Nutritional Value

Besides iodine, seaweed is a rich source of many other vitamins, minerals, and antioxidants. Adding some dried seaweed to a meal—even a very small amount—can significantly boost its nutritional value.

A 100-gram serving of nori provides:

  • 356 mg of potassium
  • 3 g of fiber
  • 6 g of protein
  • 104% RDI for vitamin A
  • 65% RDI vitamin C
  • 10% RDI vitamin B6
  • 14% RDI iron
  • 11 % RDI zinc
  • 7% RDI calcium
  • 8% RDI potassium
  • 8% RDI phosphorous

These figures might not look too impressive, but in just a small sprinkling, a couple of times per week, they can really add up.

Sea vegetables can also be a great source of antioxidants that can help protect your body against inflammation and damage caused by free radicals.

3. Promote Gut Health

Like leafy greens, seaweed can also promote a healthy gut, although it may do so in a slightly different way.

Not only a great source of fiber, seaweed can aid gut health with a unique polysaccharide sugar that can promote the growth of new, healthy gut bacterial strains. These sugars, called sulfated polysaccharides, can also promote the growth of short-chain fatty acids to provide support and nourishment for gut bacteria.

Interestingly, seaweed may act as a prebiotic and probiotic all in one!

4. May Promote Healthy Weight or Weight Loss

Because it’s a great source of fiber, seaweed may help you feel fuller for longer periods. But the benefit does not stop there. Animal studies have suggested that seaweed may have anti-obesity effects, triggered by a compound called fucoxanthin.

Fucoxanthin, found in brown seaweed, might have the ability to burn body fat, although further studies are needed, particularly in humans, to see if it has the same effect.

5. Could Potentially Help with Diabetes

One Japanese study showed that fucoxanthin may help improve blood sugar control. When given doses of either 0 mg, 1 mg, or 2 mg of seaweed oil, study participants who got 2 mg had lower blood sugar levels than those taking 0.

Another substance in seaweed that may thwart blood sugar spikes is called alginate. Animal studies have shown it might slow sugar absorption in the bloodstream.

6. Might Influence Heart Disease Risk

Seaweed, because of its fiber and antioxidant content, may lower the risk of heart disease. Research on rats has shown that seaweed supplementation can reduce “bad” LDL cholesterol and lower total triglycerides. A substance in seaweed called fucans may also prevent blood clotting, which may reduce the risk of heart attack.

So far, the findings for seaweed’s influence on heart health are preliminary, and human trials must be conducted.

Seaweed Precautions

There’s no doubt that seaweed provides a ton of nutrition and can be a real aid to your diet. But it can also be very dangerous if you eat too much of it.

Because of the high doses of iodine and heavy metals, excess consumption could lead to toxicity and illness. Therefore, it’s best taken in small amounts or eaten with foods that inhibit the uptake of iodine in the thyroid. Such foods include bok choy, broccoli, and cabbage.

Cooking seaweed, and particularly boiling it, can significantly reduce iodine content. A 15-minute boil can lower it by up to 90%.

Too much iodine can lead to an overactive thyroid, a condition known as hyperthyroidism. Symptoms can include swelling around the neck, a high temperature, hunger, and weight loss. The good thing is, lowering intake of iodine-rich foods can usually restore regular thyroid function.

The next precaution is heavy metal content. Seaweed absorbs and stores minerals at very high rates, and can therefore contain large amounts of mercury, cadmium, and lead. Some varieties can also contain higher levels of arsenic.

Consuming seaweed in small amounts protects you from the potential dangers of heavy metals, and research has shown that the heavy metal presence in average seaweed serving sizes is lower than the max concentrations most countries allow. Still, consuming it more than a couple of times per week may cause heavy metals to accumulate in the body over time.

Seaweed Recipes

1. Deconstructed Sushi Bowl

Prep Time: 15 minutes            Cook Time: 20 minutes           Servings: 1 sushi bowl, 4 servings sauce


For sauce:

1 knob fresh ginger (inch-long), peeled and chopped

2 carrots (medium-sized), chopped

3 garlic cloves

2 tbsp toasted sesame seed oil

1 tbsp honey


For sushi bowl:

1 filet wild-caught salmon, cooked (or sushi-grade raw)

1/2 avocado, sliced

1 sheet nori

1 cup rice, cooked

2 green onions, finely sliced

2 tsp rice vinegar



For sauce:

Using a high-speed blender, mix all ingredients together until smooth. Portion out enough for a sushi bowl and store the remaining amount in the refrigerator in an air-tight container for up to two days.

For sushi bowl:

  1. Cut the sheet of nori into small strips.
  2. Transfer the chopped nori to a bowl and add cooked rice, sliced green onions, and vinegar. Toss to combine.
  3. Top with salmon filet, sliced avocado, and carrot-ginger sauce.

2. Seaweed Salad


For vegetable base:

1/3 cup nori, minced

1/3 cup dulse, minced

1/3 cup red onion, minced

30 g orach, minced

30 g seashore plantain, minced

30 g sea beans (Salicornia), minced

20 g Irish moss, minced

10 g green onion in brine, minced


For dressing:

2 tbsp red wine vinegar

powdered knotted wrack, to taste

sea salt, to taste



Combine all minced veggies in a bowl. Add a pinch of the knotted wrack and sea salt and red wine vinegar. Stir well.

O’Brien, S., “7 Surprising Health Benefits of Eating Seaweed,” Healthline, May 28, 2018;, last accessed June 11, 2019.
Johnson, J., “What are the benefits of seaweed?” Medical News Today, December 6, 2018;, last accessed June 11, 2019.
Teh, Y., et al., “Analysis of iodine content in seaweed by GC-ECD and estimation of iodine intake,” Journal of Food and Drug Analysis, Jun. 2014; 22(2): 189-196;!, last accessed June 11, 2019.
Chen, L., et al., “Digestibility of sulfated polysaccharide from the brown seaweed Ascophyllum nodosum and its effect on the human gut microbiota in vitro,” International Journal of Biological Macromolecules, Jun. 2018; 112:1055-106;, last accessed June 11, 2019.
Shirosaki, M. and Koyama, T., “Laminaria japonica as a food for the prevention of obesity and diabetes,” Advances in Food and Nutrition Research, 2011; 64:199-212;, last accessed June 11, 2019.
Mikami, N., et al., “Reduction of HbA1c levels by fucoxanthin-enriched akamoku oil possibly involves the thrifty allele of uncoupling protein 1 (UCP1): a randomised controlled trial in normal-weight and obese Japanese adults,” Journal of Nutritional Science, 2017; 6: e5;, last accessed June 11, 2019.
Kimura, Y., et al., “Effects of soluble sodium alginate on cholesterol excretion and glucose tolerance in rats,” Journal of Ethnopharmacology, Oct. 1996; 54(1):47-54;, last accessed June 11, 2019.
Magalhaes, K., et al., “Anticoagulant, Antioxidant and Antitumor Activities of Heterofucans from the Seaweed Dictyopteris delicatula,” International Journal of Molecular Sciences, 2011; 12(5): 3352–3365;, last accessed June 11, 2019.
Embiricos, G., “The Definitive Guide To Edible Seaweed,” Food Republic, March 15, 2016;, last accessed June 10, 2019.
Barton, A., “Kelp is on the way,” The Globe and Mail, November 12, 2017;—but-dont-overdoit/article33281211/, last accessed June 11, 2019.
“Nori,” Precision Nutrition, 2019;, last accessed June 11, 2019.
Picard, M., “Seaweed Salad,” Food Network, 2019;, last accessed June 11, 2019.