Is All Seaweed Edible? Here's What You Should Know

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Seaweed is often thought of as the veggies or salad of the sea. There are many varieties, thousands in fact, that grow in the oceans, rivers, and even lakes, and when you eat the right ones, they are chock-a-block full of healthy goodness. Some consider seaweed an underrated superfood because your overarching seaweeds bring multiple vitamins, ranging from Vitamin A, C, and E to B12 to the table, along with a good dose of antioxidants, calcium, magnesium, and soluble fiber. But not all seaweeds are edible — some contain chemical compounds that make them toxic for consumption, or more often, they have contaminants on them that, when consumed by humans, can cause severe illness. 

You probably wouldn't have heard of these unless you head out to the waters to harvest your own seaweed, but if you see the names Desmarestia ligulata and D. viridis, stay away, as these create sulfuric acid esters, which help protect the plants from being eaten, but are dangerous when consumed by humans. You also want to stay away from any seaweeds that fall in the Bonnemaisonaceae family (for example, the Asparagopsis and Bonnemaisonia species) that contain bromine compounds and volatile halogenated iodine. Blue-green algae on lakes is also poisonous. 

While not toxic, bull kelp, giant kelp, and Alaria fistulosa contain carbohydrates that are hard for us to digest and could cause stomach issues. In general, you'll also want to avoid harvesting seaweed from industrial areas, as it can absorb heavy metals and pollutants from the water. For example, edible hijiki often contains dangerous levels of inorganic arsenic. Seaweed that has washed ashore should also be avoided as it is likely already decomposing.

Your safe-to-eat seaweeds are the ones you see on the grocery store shelves, or read on the menus of restaurants that serve them. There's quite a large variety, and they come in different forms — from fresh or dried to gels and powders. The types of edible seaweed you'll see most often are nori (including green nori, also called sea lettuce, and ogonori), wakame, kombu, dulse, hijiki, Irish moss, arame, and umibudo. Probably the most well known edible seaweed is nori — this is the one that is most often used when making sushi. It adds loads of flavor to veggies, as well as soups, dips, and dishes made with noodles. 

It also comes in powdered form, with the Japanese using it to flavor other dishes. Nori has quite a salty taste, and the unique toasting process gives it a sweetish, smoky flavor as well. For the uninitiated, experts recommend roasted nori as the absolute best nori for sushi-rolling beginners. You can buy sheets of roasted nori on Amazon. Wakame is often used in Japanese miso soup, being the little green squares that top it. It is also the primary ingredient that you will find in seaweed salad, mixed with soy sauce, sesame oil, and a few other ingredients. Like nori, it is sweet, but it also offers a desirable smooth texture and is loaded with omega-3 fatty acids. Arame is sometimes added to a seaweed salad but is actually an edible seaweed product on its own. 

You buy it as quite a pretty, black, feathery noodle-looking ingredient, and with its mild sweet taste, it's a great partner for wakame. Meanwhile, kombu is an umami staple. It's a type of kelp and has naturally occurring monosodium glutamate (MSG) in it, which we associate with an umami flavor. Because of the MSG, it's quite a salty and flavorsome seaweed, but it also makes a wonderful calming tea called konbu-cha. If you don't see any of these seaweed products on the shelves, look out for dulse, which can be used as a bacon substitute, or umibudo, which is sometimes used as a vegetarian version of fish roe because it looks like tiny grapes.