Deep Sea Nutrition: All About Seaweed

Gifts from the deep

| September/October 2001

  • Dulse seaweed is high in iodine, iron, and calcium and treats hypothyroidism.
  • Wakame seaweed is high in protein and shown to suppress tumors.
  • Hijiki seaweed is especially mineral-rich and can help reduce high blood pressure.
  • Kelp is often used as a seasoning and can help treat hypothyroidism.
  • Nori is traditionally a sushi wrapper and contains nearly 50 percent protein.

When you think of seaweed, do you have visions of slimy, brown tangles washing up on the shore? Or do you think of a nutritional powerhouse with medicinal properties? Both answers are correct, but many people don’t realize that seaweeds are beneficial to health, rapidly gaining popularity for their vitamin and mineral content, as well as their ability to prevent cancer and improve thyroid function.

Although often referred to as a vegetable, seaweed is actually any of the large multicelled forms of algae that live in fresh and salt water, especially along marine coastlines. While some may think of seaweed as part of an oceanic garden, it is different from higher land plants. Seaweeds lack true stems, leaves, and roots, and anchor themselves to rocks and reefs by rootlike holdfasts.

The three main phyla, or divisions, of seaweeds—which include some 15,000 species—are the familiar brown algae (Phaeophyta), such as kelp and bladderwrack; the reds (Rhodophyta), such as Irish moss; and the greens (Chlorophyta), which are often called sea lettuces.

Soaked in nutrition

What is it about seaweed that elevates it from simple fish food? Because seaweeds are constantly bathed in mineral-rich waters, they offer a wealth of nutrients, particularly iodine, calcium, potassium, magnesium, and iron. And depending on the variety, seaweed can be a good source of protein. A nutritional evaluation by Spain’s University Complutense of Madrid also found that seaweed is high in essential amino acids and unsaturated fatty acids.

Seaweed is packed with the immune-boosting vitamins A and C and some of the B vitamins. In fact, many types of seaweed contain more vitamin B12 than beef, chicken, or fish. A recent study by the Kochi Women’s University in Japan found that nori (Porphyra spp.), a form of red algae, is an excellent source of bioavailable vitamin B12, making it a nutritional boon for vegetarians. Seaweed is also high in a form of soluble fiber that may have antioxidant properties, particularly the fiber found in red and green algae. Another study by Japan’s Hiroshima University School of Medicine found that seaweed extracts can boost the immune system by stimulating the body’s B cells—white blood cells formed in the lymph nodes, spleen, thymus, and tonsils.

One drawback is that some types of seaweed are high in sodium. A half-cup of wakame (Undaria pinnatifida) contains approximately 900 mg of sodium, or nearly one-third of the daily sodium intake recommended by the American Heart Association. Fortunately, not all varieties pack such a sodium punch. The same amount of kelp (Laminaria spp.) dishes up 250 mg, and nori, a mere 60 mg. But if you are on a low-sodium diet or suffer from high blood pressure, you may want to check with your health-care practitioner before indulging at the sushi bar.

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