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Types of Seaweed, Nutrition, Benefits, & Side-effects

What are Edible Seaweeds?

Edible seaweeds are algae that can be eaten or used in food preparation. They are known to contain high amounts of fiber. Most edible seaweeds are marine algae, while most of the freshwater algae are actually toxic. Though some marine algae may contain acids that irritate the digestive system, others are known to have laxative and electrolyte-balancing effect.

Seaweeds are used extensively as food in the coastal regions around the world. Seaweeds have been known to be a part of dishes from the Chinese, Japanese and Korean prehistoric diets. Seaweed is also consumed in traditional European societies, in western Norway, Iceland, the Atlantic coast of France, Wales, northern and western Ireland and coastal parts of southwest England.

Seaweeds are mainly classified on the basis of their color viz. Red seaweed, green seaweed, brown seaweed and blue-green seaweed.

Types of Seaweed

Seaweeds are broadly classified on the basis of their color, which determines its other qualities. Below are the various types of Edible Seaweed:

Red Seaweed:

Red seaweed is in the phylum Rhodophyta and is red because it contains the pigment phycoerythrin. There are more than 6000 species of red seaweed. Red seaweed exists deeper underwater because it absorbs blue light.

Many types of red seaweeds are used regularly in Asian cuisines and as food additives.

Green Seaweed:

Green seaweed belongs to the phylum Chlorophyta. It has around 4,000 species. Green seaweed may be found in the marine or freshwater habitats. Some green seaweed also manages to grow on moist soil.

Examples: Sea Lettuce, Codium sp. (commonly known as ‘dead man’s finger’)

Brown Seaweed:

Brown seaweed has more than 1,800 species. It belongs to the phylum Phaeophyta. Brown seaweed are brown or yellow-brown and exist in temperate or arctic waters. Many of the edible seaweeds are Kelps, which are a type of Brown seaweed.

Examples: Kelp, Rockweed, Sargassum.

 Though there is a fourth type of seaweed, Blue-Green seaweed, most of them are toxic to both humans and animals. Therefore, it is not usually taken into account while classifying seaweeds since it isn’t edible.

Seaweed and Nutrition

Seaweeds are rich in various Proteins and Minerals. Therefore, it makes them a healthy addition to your food.

Nori, a common red algae, is rich in Vitamin A and C and helps keep your eyes and joints healthy. Iodine, Calcium, and Magnesium are minerals found in large quantities in various seaweeds.

Dried seaweed provide Fats, Fibre as well as Calories. Spirulina and Chlorella are extremely rich in proteins, namely Fibre and Magnesium.

Seaweeds also contain Omega-3 fatty acids, which act as anti-oxidants in our body.

It needs to be noted that Seaweeds also have a large amount of Iodine and Carbohydrates in them. Therefore, their consumption must be limited.

Seaweed Benefits

Seaweeds have a lot of health benefits, especially for people who suffer with Thyroid problems. Here are a few of the benefits of eating seaweed:

It Contains Protective Antioxidants:

The unstable substances in our body are known as free radicals. Antioxidants make these free radicals less reactive. As a result, they are less likely to damage our cells. Additionally, it is believed that excess of free radicals causes diseases like diabetes and heart illness. Therefore, antioxidants are necessary in order to keep these free radicals from causing unrepairable damage.

Seaweeds are rich with antioxidant Vitamin A, C and E. They also contain various beneficial plant compounds like flavonoids and carotenoids.

Thus, the Vitamins together with the plant compounds make seaweeds rich with antioxidant properties.

It Supports Thyroid Function:

Thyroid gland releases hormones to help control growth, produce energy, and repair damaged cells in our body. Thyroid depends on iodine for making hormones. Without enough iodine, you may start experiencing symptoms like fatigue, swelling of the neck and weight changes.

Seaweed is able to absorb high amounts of iodine from the ocean. Its iodine content depends mostly on where it was grown, how it was processed and also its type.

Seaweeds can contain anywhere from 11 to 1,989% of the RDI of iodine (150 mcg per day).

Natural Source of Vitamins and Minerals:

Different seaweeds have different kinds of nutrients. Sprinkling dried seaweed on your food is an easy way to add a number of vitamins and minerals to your diet.

Generally, appoximately 7 grams of dried spirulina can provide:

  • Calories: 20
  • Fats: 5 grams.
  • Protein: 4 grams.
  • Carbs: 7 grams.
  • Fibre: 3 grams.
  • Iron: 11% of RDI.
  • Manganese: 7% of RDI.
  • Copper: 21% of RDI.

Seaweed also contains small amounts of Vitamin A, C, E, and K. The protein present in some seaweeds contains all the essential amino acids. Seaweed can also be a good source of Vitamin B12 and omega-3 fatty acids.

It Can Support Your Gut Health:

It is believed that we have more bacteria in our body than human cells. An imbalance in the good and bad gut bacterias can lead to sickness.

Seaweed is rich with fibre, and it is well-known that fibre promotes gut health. About 25-75% of seaweed’s dry weight is fibre, which is way more than the amount of fibre found in fruits and vegetables.

Fibre can be used as a food source for the bacteria in the large intestine as it resists digestion.

It May Reduce Heart Disease Risk:

Heart disease is the cause of most of the deaths worldwide. High cholesterol, high blood pressure, smoking or being overweight increase your risk of a heart illness.

It is believed that seaweed may help reduce your blood cholesterol levels.

Heart diseases can also be caused because of excessive blood clotting. Seaweeds contain fucan, a type of carbohydrates, that may help prevent blood from clotting.

It May Improve Blood Sugar Levels:

Diabetes is a major health problem that occurs when your body is unable to balance your blood sugar levels.

Studies show that some seaweed oils contain 1 mg or 2 mg fucoxanthin. It also showed that people recieveing 2 mg of fucoxanthin had improved blood sugar levels.

Side Effects of Seaweed

Along with the multitude of health benefits, seaweeds also have a few noticeable side effects:

Potential for Iodine Toxicity:

Seaweeds usually have quite high amounts of iodine. Adults can tolerate upto 1.1 grams of iodine per day, whereas some seaweeds have as much as 4.5 grams of iodine in just a 1/4th cup serving.

Too much iodine can cause goiter, skin problems, rashes, nausea, diarrhea and vomiting.

Contamination With Heavy Metals:

If the seaweed grows in water rich with arsenic and other heavy metals, it can absorb these metals, thus making the seaweed impure and unhealthy. Too much consumpiont of such metals can cause heavy metal poisoning, which can be deadly.

Symptoms of heavy metal poisoning include weakness, tingling, numbness, diarrhea and nausea. Brown and black seaweed are most likely to be contaminated.

High Sodium Content:

Some brands of seaweeds have high sodium content, which can increase your risk of high blood pressure and heart disease. Supplements have even higher amounts of sodium content.

Therefore, you should be careful about the sodium content while buying seaweeds or seaweed supplements.


Thus, seaweeds have a lot of health benefits, as well as some side effects. Therefore, you should only add seaweed in your diet after consulting with your doctor.

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