Seaweed is a common ingredient in Asian cuisine that’s rapidly
gaining popularity among health-conscious Westerners.
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 protect you
from certain diseases.
This article takes a close look at seaweed and its many
What Is Seaweed?
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 the sea, lakes
and rivers. Algae from the sea is generally edible, whereas
freshwater varieties tend to be toxic.
Edible seaweed is classified by color. The most commonly eaten
types are red, green, blue-green and brown (1).
It can also range in size dramatically. Phytoplankton can be
microscopic, whereas kelp can grow up to 213 feet (65 meters)
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
Bottom Line: 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.
Common Types of Seaweed
There are many varieties of edible seaweed in the world. Here
are a few of the most common:
Nori: A red algae commonly sold in dried
sheets and used to roll sushi.
Sea lettuce: A type of green nori that looks
like lettuce leaves. Commonly eaten raw in salads or cooked
Kelp: A brown algae usually dried into
sheets and added to dishes during cooking. Can also be used
as a gluten-free alternative to noodles.
Kombu: A type of kelp with a strong flavor.
It’s often pickled or used to make soup stock.
Arame: 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: A brown algae commonly used to make
fresh seaweed salad. It can also be cooked in stews and
Dulse: 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: A green, edible freshwater algae
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
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.
Bottom Line: There are various types of
edible seaweed available. These can be consumed fresh, dried,
cooked or as a powdered supplement.
It Is High in Several Nutrients
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 vegetables of the
Seaweed’s nutrient content can vary based on where it was
grown. Therefore, different types will contain different
amounts of nutrients.
- Calories: 45
- Carbs: 10 grams
- Protein: 2 grams
- Fat: 1 gram
- Fiber: 14–35% of the RDI
- Magnesium: 27–180% of the RDI
- Vitamin K: 7–80% of the RDI
- Manganese: 10–70% of the RDI
- Iodine: 1–65% of the RDI
- Sodium: 10–70% of the RDI
- Calcium: 15–60% of the RDI
- Folate: 45–50% of the RDI
- Potassium: 1–45% of the RDI
- Iron: 3–20% of the RDI
- Copper: 6–15% of the RDI
Smaller amounts of other nutrients: Omega-3
and omega-6 fatty acids, vitamins A, C, E, phosphorus, B
vitamins and choline
Spirulina and chlorella contain twice as much protein
per portion. Unlike other types of algae, they also contain all
of the essential amino acids required by the human body. This
makes them complete sources of protein (4, 5).
Some claim that seaweed is a great plant source of vitamin B12,
a vitamin naturally found in meat, poultry, eggs and dairy.
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 (1, 11, 12, 13).
Bottom Line: Edible seaweed contains a wide
spectrum of vitamins and minerals. Dried seaweed varieties
such as spirulina and chlorella are especially rich sources
of complete protein.
Seaweed May Help Promote Thyroid Function
Your thyroid 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
Failure to get enough iodine from the diet can lead to hypothyroidism.
This can create symptoms such as low energy, dry skin, tingling
in the hands and feet, forgetfulness, depression and even
weight gain (14).
Adding seaweed to your diet can help you consume sufficient
iodine for your thyroid to function optimally (16).
The RDI of iodine for adults is 150 micrograms per day. Most
people can meet this requirement by eating several servings of
seaweed per week.
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.
Others, such as spirulina, contain very little, so don’t rely
on them as your only source of iodine.
Bottom Line: Seaweed is a great source of
iodine, which can help promote proper thyroid function.
It May Improve Heart Health
Seaweed contains certain beneficial nutrients that may help
keep your heart healthy.
A few studies have also been performed on humans.
A two-month study gave type 2 diabetics either a spirulina
supplement or a placebo every day. The supplement group’s
triglyceride levels dropped by 24% (29).
Participants in the spirulina group also improved their
LDL-to-HDL cholesterol ratio, whereas the ratio in the placebo
group worsened (29).
In another study, a daily spirulina supplement reduced
participants’ total cholesterol levels by 166% more than the
placebo group over the two-month study period (30).
Participants in the seaweed group also reduced their LDL
cholesterol levels by 154% more than the placebo group
Although these results seem promising, not all studies found
similar results and more human studies are needed before strong
conclusions can be made (31).
Bottom Line: Seaweed is a good source of
heart-healthy nutrients and may help reduce risk factors for
It May Stabilize Blood Sugar Levels
Adding seaweed to your diet may reduce your risk of developing
In one study, type 2 diabetics who took a large amount of
powdered seaweed every day had 15–20% lower blood sugar levels
at the end of the four-week study than those given a placebo
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 (38).
Higher insulin sensitivity is beneficial because it helps your
body respond better to insulin and regulate your blood sugar
levels more effectively.
Another group of type 2 diabetics who were given a daily
powdered seaweed supplement for two months experienced a 12%
decrease in blood sugar levels. No changes were observed in the
control group (29).
Hemoglobin A1C is used as a measure of your average blood sugar
levels over the last 2–3 months. A 1% decrease in A1C
represents an average blood sugar decrease of 130 mg/dl (1.5
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.
Bottom Line: The antioxidants and soluble
fiber found in seaweed may help increase insulin sensitivity
and stabilize blood sugar levels. More studies are needed to
determine optimal intake levels.
Seaweed May Help You Lose Weight
Eating seaweed regularly may help you get rid of unwanted
Researchers believe this may be due, in part, to seaweed’s
ability to affect your levels of the weight regulating hormone
Combined with seaweed’s high fiber content, this may help
decrease hunger and enhance feelings of fullness (32).
What’s more, seaweed is low in calories, but rich in glutamate,
an amino acid thought to give it a savory, umami taste
Therefore, seaweed snacks may help boost weight loss by
providing a satisfying alternative to more calorie-rich snack
Bottom Line: Seaweed may boost fat loss by
reducing hunger, increasing feelings of fullness and
preventing the accumulation of fat. Its savory taste makes it
a great low-calorie snack option.
Seaweed May Strengthen the Immune System
Seaweed may also help protect you from certain types of
Research shows that these compounds may have the ability to
fight viruses such as herpes and HIV by blocking their entry
into cells (47).
Unfortunately, not many high-quality studies have been done in
humans to support these effects.
However, neither of these studies had a placebo group, which
makes it difficult to interpret their results.
A more recent study looked at the effects of taking seaweed
supplements in HIV-positive women. Those given 5 grams of
spirulina per day developed 27% fewer disease-related symptoms,
compared to the placebo group (50).
However, no differences in immune cell levels were observed
over the 12-week study period (50).
Additional studies are needed before strong conclusions can be
Bottom Line: Seaweed may have some
beneficial effects on your immune system. However, more
research is needed.
Seaweed May Improve Gut Health
Seaweed may help improve the health of your gut in various
ways. For one, it is rich in fiber, which can help prevent
constipation and ensure smooth digestion.
are a type of non-digestible fiber that feed 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.
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 (53, 54).
Researchers also believe that the prebiotics found in seaweed
may have certain anti-inflammatory and antibacterial effects.
Bottom Line: Seaweed contains certain
compounds that may help smooth digestion, improve the health
of your gut and decrease your risk of infection with certain
It May Reduce the Risk of Cancer
The presence of seaweed in your diet may help reduce your risk
of developing certain types of cancer.
The soluble fiber found in seaweed may also help protect
against the development of colon cancer (60).
That said, very few human studies have investigated the direct
effects of seaweed in cancer patients. Very high intakes may
also increase the risk of certain cancers, particularly thyroid
Therefore, more studies are needed before strong conclusions
can be drawn.
Bottom Line: Seaweed may offer protection
against certain types of cancer. However, more research in
humans is needed.
Other Potential Benefits
Seaweed may also offer some protection against:
Metabolic syndrome: Seaweed’s potential
ability to lower weight and reduce blood pressure, blood
sugar and cholesterol may lower the risk of developing
metabolic syndrome (64).
Skin damage: Compounds in seaweed may help
protect the skin from damage caused by UVB rays from the sun.
They may also help prevent wrinkles, sun spots and premature
skin aging (65, 66, 67).
Bone and inflammatory diseases: Seaweed’s
antioxidant and anti-inflammatory effects may help reduce the
risk of developing rheumatoid arthritis and osteoporosis
Bottom Line: Seaweed may offer some
additional protection against metabolic syndrome, skin
damage, bone disease and rheumatoid arthritis.
Is Eating Seaweed Safe?
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.
It May Contain High Levels of Heavy Metals
Depending on where they’re grown, some varieties of seaweed can
contain high levels of mercury, cadmium, lead and arsenic.
The US Food and Drug Administration (FDA) regulates the levels
of these chemicals and heavy metals in fresh seaweed. However,
supplements are not regulated and may contain levels that are
detrimental to health (70).
A High Intake May Interfere With Kidney Function and Blood
Seaweed also contains vitamin K, 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.
Some Are Very High in Iodine and May Interfere With Thyroid
Kelp, dulse and kombu are types of seaweed with the tendency to
contain very high levels of iodine. For instance, 25 grams of
fresh kombu can contain close to 22 times more iodine than the
safe daily limit (1, 16).
Therefore, these varieties should not be consumed too often,
nor in large quantities.
Bottom Line: 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
Where to Find Seaweed and How to Eat It
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.
Fresh wakame and sea lettuce can be easily tossed with a little
rice vinegar, sesame oil and sesame seeds to make a delicious
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
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.
Bottom Line: 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.
Take Home Message
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.
It also contains a good amount of fiber, healthy fats and
health-promoting plant compounds that almost anyone can benefit