Seaweed, a common ingredient in some Asian cuisine, is now widely available in the United States as a snack, meal ingredient, and dietary supplement.

And for good reason. Eating seaweed is a super-healthy and nutritious way to add extra vitamins and minerals to your diet. Eating it regularly may even boost your health and help protect you from certain diseases.

This article takes a close look at seaweed and its many potential benefits.

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“Seaweed” is a general term used to describe many different species of algae and marine plants.

It can grow in a variety of waters, including seas, lakes, and rivers. Algae from the sea is generally edible, whereas freshwater varieties tend to be toxic (1, 2).

Edible seaweed is classified by color. The most commonly eaten types are red, green, blue-green, and brown (3).

It can also range in size dramatically. Phytoplankton can be microscopic, whereas kelp can grow extremely tall in length, rooted in the ocean floor.

Seaweed plays a vital role in marine life and is the primary source of food for a variety of creatures in the ocean. It has also been an integral part of human diets for thousands of years and is especially popular in Chinese and Japanese cuisines (2).

Summary

Seaweed refers to many species of algae and other marine plants. Edible seaweed can range in color and size and is a popular ingredient in Asian cuisine.

There are many varieties of edible seaweed in the world. Here are a few of the most common:

  • Nori. This is a red algae commonly sold in dried sheets and used to roll sushi.
  • Sea lettuce. This is a type of green nori that looks like lettuce leaves. It is commonly eaten raw in salads or cooked in soups.
  • Kelp. This brown algae is usually dried into sheets and added to dishes during cooking. It can also be used as a gluten-free alternative to noodles.
  • Kombu. This is a type of kelp with a strong flavor. It’s often pickled or used to make soup stock.
  • Arame. This is a different type of kelp with a mild, sweet flavor and firm texture. It can be incorporated into a variety of dishes, including baked goods.
  • Wakame. This brown algae is commonly used to make fresh seaweed salad. It can also be cooked in stews and soups.
  • Dulse. This is a red algae with a softer, chewier texture. It is used to add flavor to a variety of dishes and may also be eaten as a dried snack.
  • Chlorella. This green, edible freshwater algae is often sold as a supplement in powdered form.
  • Agar and carrageenan. These jelly-like substances obtained from algae are used as plant-based binding and thickening agents in a variety of commercially sold food products.

Spirulina is often referred to as an edible, blue-green freshwater algae and is sold in tablet, flake or powdered form.

However, spirulina has a different structure than other algae and is therefore technically considered a type of cyanobacteria (blue-green algae).

That said, since spirulina is often categorized with other types of algae in scientific research, it will be discussed alongside the other varieties in this article.

Summary

Various types of edible seaweed are available. These can be consumed fresh, dried, cooked, or as a powdered supplement.

Seaweed offers many benefits, whether you eat it as a food or take it as a dietary supplement.

Nutrient content

Seaweed is rich in various minerals and trace elements. In fact, it often contains higher levels of these nutrients than most other foods.

For this reason, many consider seaweed to be “the vegetables of the sea.”

Seaweed’s nutrient content can vary based on where it was grown. As a result, different types will contain different amounts of nutrients.

Generally, 1 cup (15 grams) of seaweed provides you with (4):

  • Calories: 45
  • Protein: 5 grams
  • Fat: 1 gram
  • Carbs: 8 grams
  • Fiber: 1 gram
  • Folate: 13% of the daily value (DV)
  • Riboflavin: 22% of the DV
  • Thiamin: 15% of the DV
  • Copper: 56% of the DV
  • Iron: 21% of the DV
  • Magnesium: 17% of the DV

Seaweed also contains smaller amounts of several other nutrients.

Iodine content can vary significantly between types, but one serving of seaweed can easily contain a day’s worth of iodine or more (5).

Some claim that seaweed is a great plant source of vitamin B12, a vitamin naturally found in meat, poultry, eggs, and dairy.

However, there’s still debate on whether the form of vitamin B12 found in algae is active in humans (6).

Finally, seaweed is a rich source of antioxidants. It also contains a good amount of sulfated polysaccharides (sPS), which are beneficial plant compounds thought to contribute to seaweed’s health benefits (7, 8, 9).

Thyroid function

Your thyroid plays several important roles in the body, including in the regulation of your metabolism.

It requires a good intake of iodine to function properly. Luckily, iodine is readily available in most varieties of seaweed. Other sources of iodine include seafood, dairy products, and iodized salt (10).

Failure to get enough iodine from your diet can lead to hypothyroidism, when your thyroid is underactive. This can create symptoms such as low energy, dry skin, tingling in the hands and feet, forgetfulness, depression, and even weight gain (11).

The recommended daily intake of iodine for adults is 150 mcg per day. Most people can meet this requirement by eating several servings of seaweed per week (10).

That said, certain varieties — such as kelp, kombu, and dulse — tend to contain very high amounts of iodine and should not be eaten frequently or in high amounts (5).

Others, such as spirulina, contain very little, so don’t rely on them as your only source of iodine.

Heart health

Seaweed contains certain beneficial nutrients that may help keep your heart healthy.

For starters, it’s a good source of soluble fiber and contains long-chain omega-3 fatty acids, both of which could be beneficial for heart health (11, 12).

In addition, several animal studies report that the sPS found in seaweed may have the ability to reduce blood pressure and prevent blood clotting (13, 14, 15, 16).

They may also help reduce LDL (“bad”) cholesterol and total cholesterol levels (14, 15).

Some human studies also report that high seaweed intakes may reduce blood pressure levels in kids and adults (17, 18).

Although these results seem promising, not all studies found similar results and more human studies are needed before strong conclusions can be made.

Blood sugar control

Adding seaweed to your diet may reduce your risk of developing type 2 diabetes.

Researchers believe that certain compounds found in seaweed may play a beneficial role in stabilizing blood sugar levels and preventing type 2 diabetes (19, 20).

One of these is fucoxanthin, an antioxidant that gives brown algae its characteristic color. This compound is thought to help reduce insulin resistance and stabilize blood sugar levels (21).

In addition, the type of fiber found in seaweed may slow down the speed at which carbs are absorbed from a meal. This can make it easier for your body to stabilize your blood sugar levels (22).

In another study, healthy participants who were given seaweed extract 30 minutes before a carb-rich meal benefited from an 8% higher insulin sensitivity than those given a placebo (23).

Higher insulin sensitivity is beneficial because it helps your body respond better to insulin and regulate your blood sugar levels more effectively.

Overall, seaweed may be beneficial for blood sugar control, but optimal dosage levels remain unclear. More research is also needed to study the effects of raw versus powdered varieties.

Weight management

Eating seaweed regularly may help you lose weight, if that’s your goal.

Researchers believe this may be due, in part, to seaweed’s ability to affect your levels of the weight-regulating hormone leptin. Combined with seaweed’s high fiber content, this may help decrease hunger and enhance feelings of fullness (24).

In addition, fucoidan, a type of sPS found in seaweed, may enhance fat breakdown and prevent its formation (25).

What’s more, seaweed is low in calories, but rich in glutamate, an amino acid that gives it a savory umami taste (26).

So, seaweed snacks may help boost weight loss by providing a satisfying alternative to more calorie-rich snack options.

Immune function

Seaweed may also help protect you from certain types of infections.

That’s because it contains marine plant compounds believed to have antioxidant, anti-allergenic, and disease-fighting properties (27, 28, 29).

Research shows that these compounds may have the ability to fight viruses by blocking their entry into cells (30).

A study in 73 HIV-positive women found that those given 5 grams of spirulina per day developed 27% fewer condition-related symptoms, compared to the placebo group (31).

However, no differences in immune cell levels were observed over the 12-week study period (31).

Unfortunately, not many other high quality studies have been done in humans to support these effects. Additional studies are needed before strong conclusions can be made.

Digestive health

Seaweed may help improve the health of your gut in various ways. For one, it’s rich in fiber, which can help prevent constipation and ensure smooth digestion.

It also contains agars, carrageenans, and fucoidans, which are thought to act as prebiotics (32).

Prebiotics are a type of nondigestible fiber that feeds the beneficial bacteria in your gut. The more good bacteria you have in your gut, the less space there is for harmful bacteria to thrive (33).

Accordingly, animal studies show that taking seaweed supplements may improve the amount of healthy bacteria and reduce the amount of harmful bacteria in the gut more effectively than other types of prebiotics (34).

Researchers also believe that the prebiotics found in seaweed may have certain anti-inflammatory and antibacterial effects (33).

This may be partly because, when feeding on prebiotics, the bacteria in your gut produce butyrate. This short-chain fatty acid is believed to have anti-inflammatory effects inside the colon (33).

In addition, certain prebiotics may have the ability to block harmful bacteria such as H. pylori from sticking to the gut wall. In turn, this may prevent the formation of stomach ulcers (34).

Cancer risk

The presence of seaweed in your diet may help reduce your risk of developing certain types of cancer.

For instance, researchers believe that seaweed may help decrease estrogen levels, potentially reducing a woman’s risk of developing breast cancer (35).

What’s more, some studies suggest that a class of compounds found in brown varieties, such as kelp, wakame and kombu, may help prevent the spread of cancerous cells (24).

That said, very few human studies have investigated the direct effects of seaweed in people with cancer. Very high intakes may also increase the risk of certain cancers, particularly thyroid cancer (37).

Ultimately, more studies are needed before strong conclusions can be drawn.

Other potential benefits

Seaweed may also offer some protection against skin damage and bone and inflammatory diseases.

Compounds in seaweed may help protect the skin from damage caused by UVB rays from the sun when applied directly to the skin. They may also help prevent wrinkles, sun spots and premature skin aging (38).

When it comes to protecting against diseases, seaweed’s antioxidant and anti-inflammatory effects may help reduce the risk of developing rheumatoid arthritis and osteoporosis (39, 40).

Summary

Seaweed may offer some additional protection against metabolic syndrome, skin damage, bone disease, and rheumatoid arthritis.

Eating fresh seaweed is considered to be safe for most people.

That said, consuming it regularly or in high amounts may cause some side effects.

Heavy metal content

Depending on where they’re grown, some varieties of seaweed can contain high levels of mercury, cadmium, lead, and arsenic (41).

The Food and Drug Administration (FDA) regulates the levels of these chemicals and heavy metals in fresh seaweed (42).

However, supplements are not as tightly regulated and may contain levels that are detrimental to health. To ensure safety, look for seaweed or algae supplements that have been third-party tested by an independent lab.

Drug interactions

Certain varieties of seaweed may contain high levels of sodium and potassium, which can be harmful to individuals with kidney disease (43).

Seaweed also contains vitamin K and anticoagulant fucoidan, which may interfere with blood-thinning medications. Those taking blood thinners should make sure to check with a doctor before making it a regular part of their diet (6).

Thyroid function

While iodine is necessary for proper thyroid function, getting too much iodine can be harmful (37).

Kelp, dulse, and kombu are types of seaweed with the tendency to contain very high levels of iodine. With regular consumption of these types of seaweed, it’s possible to consume enough iodine to inhibit regular thyroid function (5).

So, these varieties should not be consumed too often, nor in large quantities.

Autoimmune disorders

For people with autoimmune disorders — which are caused by the immune system attacking a body system or part after wrongly perceiving it as a threat — spirulina may not be a good choice.

Autoimmune disorders include type 1 diabetes, Hashimoto’s thyroiditis, lupus, multiple sclerosis, rheumatoid arthritis, and many others.

Spirulina’s immune-strengthening properties can actually cause a worsening of autoimmune symptoms as the immune system gets stronger and continues its attack on the body’s own cells. This is why it and other blue-green algae products should be avoided by people with autoimmune disorders (44, 45).

Summary

Seaweed is considered safe for most people. Limit your intake if you tend to prefer high iodine varieties, or if you take blood thinners or have kidney issues.

Seaweed can be purchased fresh or dried from most Asian supermarkets. Nori, the type commonly used to roll sushi, may also be available at regular grocery stores.

In addition to their use for sushi, nori sheets can also easily be used to replace tortilla bread when making wraps.

You can toss fresh wakame and sea lettuce with a little rice vinegar, sesame oil, and sesame seeds to make a delicious salad.

Dried nori or dulse make for nice savory snacks. Or try crumbling them over salads to add a dash of umami flavor.

Spirulina and chlorella can be incorporated into smoothies, while kelp can be used instead of salt to add flavor to just about anything.

Many types of seaweed can also be incorporated into warm dishes, including soups, stews, and baked goods. There’s no right or wrong way to go about it.

Summary

Seaweed can be purchased in most Asian supermarkets. It can be incorporated into a wide variety of dishes including soups, salads, smoothies, stews, and even baked goods.

Seaweed is a worthy addition to your diet. There are many different and interesting varieties that are low in calories yet very rich in nutrients.

Seaweed also contains a good amount of fiber, healthy fats, and health-promoting plant compounds that almost anyone can benefit from. Best of all, it’s extremely versatile — you can eat seaweed as a snack, as part of a recipe, in shakes and smoothies, or as a supplement.