If you frequent Japanese restaurants, you may know seaweed as the wrapping around sushi rolls or as the silky green strips floating in your miso soup. Or maybe in grocery stores you’ve noticed packages of dried seaweed along with a growing assortment of seaweed snacks. Touted as a hot new superfood, seaweed is making its way into the U.S. market.
No question about it, seaweed is a nutritional powerhouse. This isn’t news in Asia, where sea vegetables are eaten daily, just as they have been for thousands of years. From Japan, Korea and Vietnam to Malaysia, the Philippines and across the South Pacific, sea vegetables are revered as much for their flavors as for their nourishing powers. Western cultures would do well to embrace this remarkably healthy, versatile food from the sea.
Seaweed is classified as algae, and there are more than 30 commonly eaten varieties categorized by color: brown, red or green. Each is unique in its shape, taste and texture, but all types contain a rich store of essential minerals that includes calcium, copper, iodine, iron, magnesium, manganese, molybdenum, phosphorus, potassium, selenium, vanadium and zinc. Sea vegetables also provide a potent array of vitamins, including B vitamins riboflavin and pantothenic acid; vitamins A and E; and vitamin C, which aids iron absorption. A single serving of seaweed contains almost one-fifth of the daily recommended value of vitamin K.
The nutrients in sea vegetables make them useful for maintaining good health and for fighting disease. Seaweed is rich in phytonutrients, including sulfated polysaccharides that are known to have significant anti-inflammatory, antiviral and cardiovascular benefits. A 2011 review of 100 studies on the benefits of seaweed published in the American Chemical Society’s Journal of Agricultural and Food Chemistry reported that seaweed may be a better source of bioactive peptides than milk products, and it validated the usefulness of seaweed for lowering blood pressure and promoting heart health. Research has shown that eating seaweed may help protect against certain cancers, too. The folic acid in seaweed is thought to lower the risk for colon cancer, and its cholesterol-lowering properties may reduce the risk of estrogen-related cancers, such as breast cancer.
Seaweed can play a role in weight loss because it is very low in calories and fat (8 calories and 0 grams of fat in a ¼-cup serving), provides some fiber (10 sheets of nori have 1 gram of fiber) and contains alginate, an anionic polysaccharide shown to cut fat absorption. Limited research suggests brown algae vegetables that are rich in the minerals iodine and vanadium may help regulate carbohydrate metabolism and blood sugar.
Healthy as seaweed is, its high concentration of certain nutrients can be problematic for some. For example, overconsumption of vitamin K can interfere with medications such as warfarin, which is widely prescribed to treat and prevent blood clots. Two tablespoons of the red seaweed dulse contain 34 times the potassium as the same amount of banana, so anyone with kidney problems should avoid it. And while seaweed’s iodine content makes it especially beneficial for thyroid health, consuming too much iodine can have the opposite effect. According to a 2011 study published in the American Journal of Clinical Nutrition, too much iodine in the diet (400 micrograms or more a day) may actually trigger hypothyroidism.
Most commercial seaweed is grown in Asia, either cultivated in commercial farms or harvested wild in clean waters. The USDA regulates sea vegetables, so look for a certification mark on the package when purchasing seaweed products. As for seaweed pills, since the FDA does not regulate supplements, it is possible that the seaweed may have come from waters contaminated with heavy metals such as arsenic.
Seaweed Varieties and Culinary Uses
Because Japan is the leading producer and exporter of sea vegetables, most varieties are known in the U.S. market by their Japanese names.
The mildest among seaweeds, nori is best known as the dark green wrapping on sushi rolls. Since nori is high in omega-3 fatty acids (about three sheets contain 0.01 grams of ALA), it helps protect the skin and prevent dryness. It is also rich in B12 and vitamin C. Sushi lovers will be happy to hear that nori is lower in iodine than other seaweeds, so eating a few rolls a week should not impact thyroid health.
The most widely consumed seaweed, kelp comes in many varieties — usually dried into sheets that are added directly to a dish during cooking or soaked in water to make it pliable for eating. Kombu is a brown kelp popularly used as a hearty, mineralrich flavoring for broths and soups, and in Japan it is sometimes eaten fresh. Arame, another species of kelp that is characterized by its dark brown strands, has a mildly sweet flavor and firm texture that makes it an appealing addition to many dishes, from soups and casseroles to baked goods. In Korea and Japan, chefs prepare fresh arame by tossing it with sesame oil and serving it over chopped lettuce. Kelp also comes in flake or granulated form and is used as a salt substitute and a shakable mineral supplement. Kelp noodles, which do not require cooking, are tasty and do not contain sugar or fat; a 1-cup serving has fewer than 10 calories. They are cholesterol- and glutenfree, and contain 15 percent of the daily recommended intake of calcium.
Kelp is very high in iodine — a quarter of a teaspoon contains 2,000 percent of the RDA. It can be a welcome addition to a diet if more iodine is needed, but steer clear if there are medical reasons to limit iodine.
Dulse is a red seaweed that grows abundantly along the rocky North Atlantic and Northwest Pacific Coasts. Dulse has a soft, chewy texture. One way to enjoy fresh dulse is to sauté it with butter and garlic. Most dulse is consumed in dried flake form as a flavoring for soups. Dulse has considerably less iodine than kombu, and it is a good source of magnesium and calcium.
Seaweed snacks, such as roasted seaweed, offer a healthy alternative to chips by providing a salty crunch that’s low in both calories and fat.
Filipino Miso Soup
Recipe developed by McKel Hill, MS, RD, LDN
12 cups water
1½ cups carrots, cut into matchsticks
1 pound baby bok choy, cut into ½-inch slices
8 ounces fresh shiitake mushrooms
5 ounces soba noodles, uncooked
3 ounces firm tofu (sprouted tofu, if available), cut into small cubes
8 tablespoons mellow white miso
¼ cup dulse seaweed, cut with scissors
½ tablespoon wakame or other seaweed
1 tablespoon ginger root, peeled and minced
4 cloves garlic, minced
4 scallions, sliced diagonally
½ teaspoon sesame oil
- In a large, nonstick soup pot, heat sesame oil and add ginger and garlic. Let cook for about 1 minute. Add in the cubed tofu and cook until the sides are golden.*
- Add water, wakame, dulse, carrots, bok choy and fresh mushrooms and bring to a simmer. Cover and let simmer for about 15 minutes or until carrots are tender. Add the noodles, cover and cook until noodles are tender, about 5 to 7 minutes.
- Place the miso paste into a small bowl and add 1 cup of the hot soup broth. Stir until there are no miso lumps. Add the mixture back to the pot. Heat through but do not boil. Serves 8.
*If you prefer a softer tofu texture, wait to add tofu with the vegetables.
Sesame Wakame Salad
Recipe developed by Karman Meyer, RD, LDN
1 ounce dried wakame
½ medium cucumber
1 medium carrot
2 tablespoons sesame oil
2½ teaspoons rice wine vinegar
1¼ teaspoons tamari
¾ teaspoon agave nectar
1 clove garlic, minced
1 teaspoon sesame seeds, toasted
- Rehydrate wakame per package directions. Drain all liquid from seaweed and place into a large mixing bowl. Set aside.
- Remove seeds from cucumber and cut into 1⁄8-inch-thick slices. Using a vegetable peeler, shred the carrot into short strands. Add cucumber and carrot to wakame.
- In a small bowl, combine sesame oil, rice wine vinegar, tamari, agave nectar and garlic. Whisk together and then pour over vegetables. Add toasted sesame seeds. For the best flavor, refrigerate for 24 hours before serving. Serves 5.