Written by Lisa Dreher, MS, RDN, LDN
Seaweed: An Underestimated Nutritional Powerhouse

Seaweed: An Underestimated Nutritional Powerhouse

What are sea vegetables?

Sea vegetables, more commonly known as seaweed, are various forms of algae. They have made their way into the diets of people all over the world due to their versatility, surprisingly delicious taste, and nutrient density. Japanese cultures have been eating seaweed for over 10,000 years, while other countries located near water, such as Ireland, Iceland, and New Zealand, have also enjoyed seaweed for thousands of years. From a science standpoint, there are three main kinds of seaweed: green, red, and brown algae.

  • Green algae. This type of seaweed gets its green color from chlorophyll and the most commonly eaten form is sea lettuce.
  • Red algae. The most commonly eaten form is nori, but this category also includes agar-agar and dulce.
  • Brown algae. The most commonly eaten form is kombu/kelp, but it also includes wakame, hijiki, and arame. This type accumulates more iodine than other sea vegetables and can range anywhere from 110 to 1,500 micrograms (mcg) of iodine per gram.


What are the health benefits of seaweed?

  • Seaweed is high in minerals and vitamins including iodine, copper, calcium, magnesium, manganese, vitamin B2, and vitamin C.
  • They are one of the few food sources of the less well-known mineral vanadium. Preliminary research shows that vanadium may improve the body’s sensitivity to insulin and decrease the body’s production of glucose.
  • They contain unique phytonutrients and antioxidants, which are needed to protect our cells and DNA against damage.
  • Seaweed contains fucoidan (a complex starch, or polysaccharide) that has anti-cancer properties. This also offers anti-inflammatory properties that seem to be especially beneficial in those with osteoarthritis and cardiovascular disease.
  • Sulfated polysaccharides found in seaweed possess natural anti-viral properties by blocking the replication of viruses, which have been studied with the herpes simplex virus (HSV) 1 and 2.
  • Seaweed favorably alters estrogen and phytoestrogen metabolism, which if eaten in moderate amounts over time, can be protective in women at risk of estrogen-sensitive breast cancers.
  • Can positively alter the gut bacteria.


Can you eat too much?

Excessive amounts of iodine can have a detrimental impact on the thyroid. However, a balance of iodine in the body is needed for optimal thyroid and overall health. Therefore, eating moderate amounts of seaweed is typically recommended. If you have a known thyroid condition, you should have your iodine levels checked and periodically monitored.

Every individual is different, as are their iodine needs. For those who need less, significantly limit or avoid brown varieties such as kelp and opt for red seaweed varieties which contain less iodine per gram. For healthy individuals without a thyroid condition, the recommended daily allowance (RDA) for adults 19 years and older is 150 mcg and the upper limit is 1,100 mcg. All seaweed varies as far as its iodine content. A 1 gram sheet of seaweed can contain anywhere from 11 to 1,989% of the RDA for iodine. Here is the average iodine content of three common seaweeds:

  • Nori contains 37 mcg per gram
  • Wakame contains 139 mcg per gram
  • Kombu contains 2,523 mcg per gram

Additionally, excess amounts of polysaccharides may contribute to gas, bloating, and gut discomfort in certain individuals, such as those with small intestinal bacterial overgrowth, or SIBO. While the benefits of eating seaweed outweigh the risks, it is important to try a small amount of seaweed first, then adjust based on how you feel. On the flip side, kombu may actually improve the digestibility of beans if added to water used to soak the beans.

Are there any special considerations when choosing seaweed?

Seaweed can act like a sponge for heavy metals such as arsenic, lead, mercury, and cadmium. Although trace amounts of arsenic are present in a lot of seaweed, these heavy metals can be much more concentrated in seaweed that is grown in water polluted by industrial waste as well as those that are not organic. They can also be a concentrated source of pesticides if not purchased organically. I recommend always choosing organic seaweed from companies that are dedicated to producing high-quality products in clean waters such as the Gulf of Maine and North Atlantic. Two of my favorite brands include Maine Coast Sea Vegetables and SeaSnax.

Seaweed recipes!

Many people only see or eat seaweed when they go to a Chinese or Japanese restaurant and get sushi or seaweed salad. While these can be very tasty, there is so much you can do with seaweed at home! Dr. Hyman has created several recipes that contain seaweed over the years, and I’ve compiled my favorites here:

I hope you’ll enjoy these delicious recipes and realize what a secret superfood seaweed really is!

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