Is Seaweed Healthy?

Photo: Getty Images / MirageC

In Japan, seaweed is an important part of the diet (it's also commonly eaten in Chinese and Korean cultures). But in the U.S. it's mostly just considered a health food or something we eat in Asian restaurants in sushi, seaweed salad, miso soup, etc.

Seaweed deserves a sliver of real estate in your grocery cart, though. It's highly nutritious, delivering healthy amounts of fiber, omega-3 fats and key amino acids (the building blocks of protein), as well as vitamins A, C, E and the Bs, which aren't usually found in "land" vegetables. Seaweed is also good for the minerals magnesium, potassium, phosphorus, iodine, zinc and-unfortunately-sodium. It's also incredibly sustainable to grow-using just the sun and what nutrients are in the water, no inputs necessary. But perhaps most importantly: it's an ingredient that when harnessed appropriately adds great flavor depth and umami to a dish.

What are the different types of seaweed?

Seaweed is not a plant, but a type of algae that typically grows on rocks or other hard surfaces in and around coastal areas. There are three main groups of seaweed-green, red and brown-and within each group there are many types of seaweed that together add up to around 12,000 species of seaweeds.

Here are some of the more commonly found (and commercially available) seaweeds that we eat:

Nori

This is the purplish-black seaweed you see wrapped around your sushi rolls. It's one of the more nutritious seaweeds (brimming with vitamin A and with some B12) and has a decent dose of protein coupled with very little sodium (it's washed away during processing into dried sheets).

Kombu

This is actually the name for a mix of five different species of brown seaweed (often very long, very wide and flat-almost lasagna noodle-like). Kombu is lower in protein and vitamins than nori, but it brings solid amounts of iron and iodine.

Wakame

Touted by some as the most versatile edible sea vegetable, wakame is what you find in miso soup and seaweed salad. It's pretty high in fiber (more so than nori or kombu), but not much is notable beyond that, as many of its vitamins and minerals are lost when it's processed.

Dulse

Red with leathery "leaves," dulse is fairly nutrient-packed-delivering iron, iodine, potassium, and vitamin B12, many of which we don't get enough of in our diets.

Aonori

This dried green seaweed is less familiar to Westerners. You'll typically find aonori sold as dried flakes to be used as a condiment or garnish, so it's an excellent introduction and makes for a gateway into seaweed appreciation. Plus, aonori is packed with B vitamins and has a moderate protein amount.

Where can you buy seaweed?

"For the best selection, shop at Asian markets," says Ann Taylor Pittman, a food writer and award-winning cookbook author. "You'll typically be limited to nori (used for sushi) at most supermarkets, though you can find a slightly larger variety at Whole Foods-which often carries kombu and sometimes wakame." And there's always online if you can't find what you're looking for in nearby stores.

How can you use seaweed?

There are so many ways to eat seaweed, but which type often points you in the direction of how you should eat it. "Nori is best for sushi rolls, hand rolls and-once toasted-seaweed snacks," says Pittman. "Kombu is great for vegetarian stock, but it's typically pretty salty, by the way. Use wakame in seaweed salad and stirred into miso soup or seaweed soup," she adds.

Wait, what is seaweed soup? "My mom, who is Korean, says that this is often referred to as birthday soup (and yes, enjoyed on one's birthday) and typically given to a woman who has just given birth," explains Pittman. "The nutrients in it are said to speed the new mom's recovery. To make seaweed soup, my mom always starts by sautéing some "chewy" pork-slivers of shoulder, for example-with garlic, then adding water, a splash of sesame oil, a splash of soy sauce and a handful of wakame that's been soaked in cold water to hydrate. This simmers for about 20 minutes till the flavors meld."

What are the health benefits of seaweed?

Seaweed is nutrient-packed, yet how much of the different nutrients you get varies slightly between seaweed groups and species. There is also growing body of science that suggests elements of, and compounds in, seaweed have true health-promoting benefits. For example, seaweed is well-known for being fiber-rich, and research has associated eating foods enriched with fiber-specifically from seaweed-with aiding in prevention of colon cancer, type 2 diabetes, obesity and cardiovascular disease. There are compounds in seaweed believed to have potent antioxidant benefits. Other research, this in animals, showed that adding seaweed to the diet helped to improve blood cholesterol levels in rats even while they were eating a high-fat and high-cholesterol diet. And still other research found that adding seaweed to the diets of both people and animals helps with weight loss and blood pressure.

Read more: Healthy High-Fiber Foods

Is there anything to watch out for?

Part of what makes seaweed so sustainable is that it doesn't require much of anything to grow because it readily absorbs what it needs from the sun and water. But the other side of the coin is that seaweed can also easily absorb toxic metals like mercury, arsenic, aluminum, cadmium, copper and lead-all of which can be quite harmful-from the water in which its growing. Research has found these metals in various seaweeds, grown in different locations around the world, but most studies have concluded that eating 4 to 5 grams a day of dehydrated seaweed shouldn't pose a risk to healthy adults. That's about two sheets of dried sushi nori.

Another thing to be mindful of about seaweed is shellfish allergies. If you, or someone that you're cooking for, has a shellfish allergy, they may want to avoid seaweed because particles of shrimp and other crustacean shells could remain in seaweed even after it's harvested and processed.