Eating Seaweed: Health Benefits and Side Effects

Benefits of seaweed: Easy to eat and highly nutritious. May help with thyroid health, digestive health, weight loss, and blood sugar management.

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June 12, 2024
February 26, 2023
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Seaweed is a type of algae that grows in the ocean and is abundant with minerals that are easy for the body to break down. Adding seaweed to the diet may have several health benefits, including improving thyroid function, digestive health, and weight loss.

What is Seaweed? 

Seaweed is a type of marine algae that grows along rocky shorelines worldwide. It has been used in Asian cuisine for centuries in Japan, Korea, and China. However, its popularity is increasing in other parts of the world.

There are many different types of seaweed, including:


This kelp species is native to the cold, temperate coasts of the northwest Pacific Ocean. It has a subtly sweet but distinctive and strong flavor and texture as an edible seaweed. It is most often served in soups and salads. 


Dulse has been a popular snack in Scotland and Ireland for generations. It is red in color and grows on the northern coasts of the Atlantic and Pacific Oceans. 


Kombu is dried edible sea kelp mainly used to make broth in Japanese cooking. It has a subtle but savory taste when boiled.


Kelp is a large, brown seaweed that grows in shallow waters on the coast worldwide. The color, flavor, and nutrient profile slightly differ from the nori used in sushi. 

Sea lettuce

Sea lettuce can be eaten fresh; however, it is much more flavorful when dried. It has a cucumber-umami flavor. This seaweed is dehydrated and eaten as crisps or crumbled over soups, stews, and salads.


One of the most commonly consumed seaweeds, Nori is a red seaweed that usually comes pressed into thin, dark green or black, dried sheets. These are often eaten as a snack or used to make sushi rolls.


Arame is a dark brown seaweed that comes in strands. It is used in Japanese cuisine. Its mild flavor makes it versatile for many uses.


Chlorella is a single-celled, freshwater alga that grows in Taiwan and Japan. It is commonly used as a health supplement.


The Nutritional Profile of Seaweed 

Seaweed is one of the best foods for metabolic health. The nutritional profile of seaweed depends upon the location and water in which it grows. However, all seaweeds have a robust vitamin and mineral profile.

Seaweed is rich in antioxidants, vitamins, minerals, and protective pigments. It contains small amounts of vitamins A, C, E, and K and folate, zinc, sodium, calcium, and magnesium. It is also a source of iodine, a trace mineral important for the health and function of the thyroid.1

The nutrients per two-tablespoon serving of Wakame seaweed:

  • Calories: 4.5
  • Fat: 0g
  • Sodium: 87.2mg
  • Carbohydrates: 0.9g
  • Fiber: 0g
  • Sugars: 0g
  • Protein: 0.3g
  • Magnesium: 10.7mg
  • Calcium: 15mg
  • Iron: 0.2mg

6 Health Benefits of Eating Seaweed

1. May improve gut health

Seaweed is a good source of fiber and polysaccharides that promote gut health. Fiber is about 25-75% of seaweed’s dry weight, depending on the type.

Fiber is indigestible and can be used as a fuel source for good gut bacteria in your large intestine. Sugars found in seaweed called sulfated polysaccharides have been shown to increase the growth of healthy gut bacteria.6,7,8

The polysaccharides also increase the production of short-chain fatty acids (SCFA), which support the cells in the lining of the gut.9,10

2. May support weight loss

Seaweed is low in calories and high in fiber. Fiber helps increase satiety and keeps you feeling full for longer. It also contains fucoxanthin, which may contribute to increased metabolism and fat loss.11

3. May boost immune health

Gut health and immunity are closely related. A healthy gut microbiome can bolster the immune system.12

Some researchers believe that seaweed may help to boost the immune system by fighting viruses and preventing illness. More studies are needed, however.

4. May prevent heart disease, type 2 diabetes, and cancer

Seaweed may help reduce blood cholesterol levels.13

It also contains carbohydrates called fucans, which are shown to prevent excessive clotting that may cause heart disease.14,15

Some animal studies suggest that seaweed may also help lower blood pressure.

Fucoxanthin, alginate, and other compounds found in seaweed may help lower your blood sugar levels and reduce your risk of diabetes.16

Eating seaweed may reduce the risk of developing certain cancers. The compound fucoidan may have antioxidant and anti-tumor effects. Evidence is limited, and more conclusive research is needed.17

5. May improve thyroid function

The thyroid gland releases hormones that control growth, metabolism, reproduction, and repair cell damage. However, the thyroid needs iodine to make these hormones.3,4

Seaweed is a good source of iodine. It also contains the amino acid tyrosine, which is used alongside iodine to make two key hormones that help the thyroid gland do its job properly.5

6. Packed with protective antioxidants

Oxidative stress and excess production of free radicals are associated with increased disease risk, particularly for type 2 diabetes and heart disease.18

Seaweed contains various antioxidants, including vitamins A, C, and E, carotenoids, and flavonoids. These antioxidants protect your body from cell damage.19

Seaweed and Blood Sugar Levels

Fiber-rich foods like seaweed may help manage diabetes. High fiber consumption helps regulate blood sugar levels and insulin levels. Consuming seaweed may help increase fiber intake without a large increase in calories.6

The fiber found in seaweed may also help manage hyperglycemia and prevent blood sugar spikes.

One animal study found that specific compounds in one type of seaweed may directly decrease markers of type 2 diabetes, such as high blood sugar.21

These compounds may also lower diabetes risk factors like inflammation and insulin sensitivity. Further research in humans may help provide stronger evidence for using these compounds.

Potential Side Effects of Seaweed

Although seaweed is considered a highly nutritious food, there may be some downsides to consuming too much. This is mostly due to the potential absorption of water contaminants.

Excessive amounts of iodine 

While the body needs iodine to function properly, excessive amounts can be just as detrimental to health as a deficiency. Seaweed contains high levels of iodine that can be dangerous when over-consumed.

Seaweed is water-soluble, so cooking it can alter the iodine content. When kelp is boiled for 15 minutes, up to 99% of its iodine content can be lost.22 If you have symptoms like swelling in the neck or unexpected weight fluctuations, lower your intake of iodine-rich foods and talk with your doctor.

Heavy metal load

Seaweed absorbs and stores many nutrients and minerals from its environment. That is why it has such a robust nutrition panel.

This ability to absorb minerals from the environment can contribute to a heavy metal load. Seaweed may contain large amounts of toxic heavy metals such as cadmium, mercury, and lead.23

However, the heavy metal content of seaweed is usually below the maximum allowable threshold in most countries.24 

Recent research examining the heavy metal content of 8 different seaweeds from Asia and Europe found levels that posed no serious health risks.25

If you eat seaweed often and in high quantities, these heavy metals could potentially accumulate in your body over time.

If possible, buy organic seaweed, as it’s less likely to contain significant amounts of heavy metals. 

Medication interferences 

Seaweed is high in potassium, which can harm people with kidney disease. Seaweed also contains vitamin K, which could interfere with blood-thinning medications such as Warfarin.

You may want to limit or avoid seaweed consumption if you have chronic kidney disease or are taking blood thinners. 

How to Eat Seaweed 

Seaweed is very versatile, and since there are various types with different flavor profiles, there are many ways to enjoy it. 

  • Eat it as a snack – Nori and dulse can just be eaten out of a bag. They make a great on-the-go snack that is highly nutritious. 
  • Seaweed salad – Most types of seaweed can be made into a Japanese-style salad with vinegar, sesame oil, ginger, and garlic. If you purchase dry seaweed, it must be rehydrated by soaking it in water. 
  • Soups – Seaweed tastes delicious in broth, which makes it seaweed soup.
  • Sprinkle it on other foods – Seaweed flakes can be sprinkled on salads, rice, soups, or other dishes.

Fresh seaweed should be handled and prepared like other leafy greens. Wash fresh seaweed under running water before consuming or preparing it. Keep fresh seaweed stored in the refrigerator.

Dried seaweed should be kept in an airtight container after opening. Follow the expiration dates listed on the package for maximum freshness.

FAQs on Seaweed

1. How much seaweed can you eat?

The main concern for eating too much seaweed is excess iodine consumption. For healthy individuals without a thyroid condition, the recommended daily allowance for iodine for adults 19 years and older is 150 micrograms, and the upper limit is 1,100 micrograms.

  • Nori contains 37 mcg of iodine per gram
  • Wakame contains 139 mcg of iodine per gram
  • Kombu contains 2,523 mcg of iodine per gram

2. Does eating seaweed affect intestinal motility?

Seaweed is high in fiber, so it may affect intestinal motility. Fiber tends to slow gastric emptying in healthy individuals.

3. Is seaweed beneficial for the skin?

Seaweed is a popular hydrating ingredient in skincare products. Seaweed is a humectant and draws moisture into skin cells, while polysaccharides absorb water and bring it to the skin. It can provide long-lasting hydration for the skin.

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Topics discussed in this article:


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About the author

Victoria Whittington earned her Bachelor of Science in Food and Nutrition from the University of Alabama and has over 10 years of experience in the health and fitness industry.

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