What Is Seaweed?
Seaweed is a general term that describes algae and marine plants that grow along rocky shorelines around the world. There are many types, including red (Rhodophyta), green (Chlorophyta), blue-green, and brown (Phaeophyceae).
Seaweed has been an important part of the diets of coastal people since prehistoric times. Today, more than 145 varieties are eaten worldwide.
Some of the most common edible seaweeds include:
- Sea lettuce
While seaweeds grow in all parts of the world, they’re most common in East Asian and Pacific cuisines, where they’re used in sushi, salads, soups, and stews.
While seaweed isn't as popular in the U.S. as in Asian countries, many Americans enjoy seaweed as a tasty and nutritious part of their diets. You can also buy many types of seaweed extracts and supplements.
Seaweed is an excellent source of iodine. This trace mineral is important for the health of your thyroid, a gland in your neck that helps regulate your metabolism. Your body doesn’t make iodine, so you must get it from food or supplements.
Scientists haven't extensively studied most of the possible health benefits of seaweed. But potential benefits include:
Improves thyroid function
Thyroid hormone helps regulate many of your body's functions, ranging from menstrual cycles to temperature control. Without enough iodine, your thyroid can’t make enough of this hormone (a condition called hypothyroidism). You could also develop a goiter, a visible enlargement of your thyroid. Iodine is especially important during pregnancy since it's involved in fetal brain development. Young children who have iron deficiencies are at risk for intellectual disabilities and stunted growth.
May improve gut health
Seaweed contains carbohydrates that act as prebiotics, which are nondigestible fibers that feed the healthy bacteria in your digestive tract. Sugars found in seaweed help boost the growth of this “good” bacteria and increase the level of short-term fatty acids that keep the lining of your gut healthy.
May improve heart health
Early studies have found a link between seaweed intake and a lower risk for heart disease. Some findings indicate that polyphenols, compounds found in seaweed, could help lower blood pressure, LDL or “bad” cholesterol, and total cholesterol levels.
May help stabilize blood sugar levels
There's some evidence that compounds in seaweed could help with blood sugar control. Early studies have shown that plant chemicals called polyphenols may help reduce blood glucose. Some research indicates that fucoxanthin, an antioxidant found in some types of seaweed, also may play a role in blood sugar control.
May boost your immune health
While there's limited research into this effect, seaweed contains antioxidants and prebiotics that are known to contribute to a healthy immune system. But it's not clear how well the human body processes these components from seaweed.
May reduce cancer risk
Early studies have found that fucoidan, a carbohydrate found in brown seaweed, has anti-cancer properties. Some other components of seaweed, such as folic acid and polyphenols, are also thought to help protect against cancer. But no clear link has been established.
The nutrition content of seaweed varies based on what kind it is and where it grows. But every type contains vitamins and minerals, including:
- Vitamin A
- Vitamin B2
- Vitamin B5
- Vitamin C
- Vitamin E
Seaweed is especially rich in Vitamin K, with one serving offering up to 1/5th of the daily recommended value. It's also high in both protein and fiber, though serving sizes usually aren't big enough to make it a major source. And it contains antioxidants (compounds that help fight cell damage) in the form of Vitamins A, C, and E, as well as in the pigments that give seaweed its colors. It's also low in calories.
Nutrients per serving
A 2-tablespoon serving of wakame seaweed has:
- Calories: 5
- Protein: 0 grams
- Fat: 0 grams
- Carbohydrates: 1 gram
- Fiber: 0 grams
- Sugar: 0 grams
Eating seaweed is safe for most people. But there are a few things to watch out for:
Too much iodine. While iodine is vital for thyroid health, too much of this trace mineral can lead to hypothyroidism. We only need iodine in small amounts -- ideally, less than 1,100 micrograms a day. In particular, children, infants, and people who have thyroid disorders should avoid taking in too much iodine.
It may interfere with certain medications. Seaweed is rich in potassium, which is generally healthy but can be harmful to people with kidney disease. Seaweed also contains vitamin K, which can interfere with blood-thinning medications such as warfarin (Coumadin).
Some varieties may have high levels of heavy metals. Seaweed could contain high levels of arsenic, cadmium, mercury, or lead, depending upon how and where it was grown. The FDA regulates the heavy metal contents in fresh seaweed, but not in seaweed supplements. Ask your doctor before you take a new dietary supplement.
How to Use Seaweed
Many grocery stores carry some forms of dried seaweed. You may find dried seaweed snacks, nori for sushi, or dried dulse flakes. Many Asian food stores carry a variety of dried and fresh seaweed products.
There are many ways to add seaweed to your diet, including:
- Make a soup broth with dried kelp or kombu.
- Mix fresh arame and wakame with vinegar, sesame oil, scallions, and garlic for a seaweed salad.
- Top your meals with a mix of ground nori, kombu, dulse, salt, black pepper, and sesame seeds.
- Snack on dried nori.
- Add kombu to cooked beans.
- Make homemade sushi.
- Make a vegan “tuna” salad with chickpeas, vegan mayonnaise, celery, red onion, salt, pepper, and dulse flakes.
The traditional Japanese seaweed salad may look different from what you find in many American sushi restaurants. The Japanese dish includes different sea vegetables in a rice vinegar dressing.
It's a simple dish to make at home. Common ingredients include:
- Mixed dry seaweed
- Rice vinegar
- Toasted sesame oil
- Soy sauce
- Ginger juice
- Toasted sesame seeds
Seaweed snacks are made by roasting or frying dried seaweed until it's crispy. Commercial types tend to contain lots of sodium and additives but are still healthier than many types of chips and other crunchy snacks. To make your own seaweed snacks, roast dried nori on an oiled baking sheet until crisp (this only takes a few minutes).
Seaweed soup, or miyeok guk, is a well-known Korean dish made with brown seaweed or wakame. You make it by soaking dried seaweed until soft, then cooking it with beef (or another protein), sesame oil, and seasonings.