Benefits Of Seaweed: Nutrition, Side Effects & How To Eat 2025

Functional foods are gaining attention worldwide, and nutraceutical industries are speeding up their research and development studies of promising foods. Noncommunicable diseases are the major public health problem for many countries, with high morbidity, mortality, and health costs. However, the risk factors for these diseases, such as obesity, diabetes, high blood pressure, and cardiovascular conditions, e.g., hypertension and high cholesterol, can be reduced by these foods. Seaweeds are one of these promising functional foods.

Edible seaweeds,^[1] or macroalgae, are rich and sustainable sources of nutrients and functional biochemicals in the diet. They are also the main ingredient for meals in some Asian countries.

Epidemiological studies^[2] have demonstrated that the cancer prevalence of certain cancers is less in Asian countries compared to Western countries. Their dietary habits that include many kinds of seafood may be a factor in lowering cancer and chronic disease risks.

Seaweed benefits are mainly coming from its macro and micronutrients. These can be identified as dietary fiber and bioactive compounds, such as polyphenols or iodine sources for humans.

Benefits Of Eating Seaweed

1. Thyroid health
2. Appetite control
3. Regulation of metabolism
4. Immune effects

Health Benefits Of Seaweed

Edible seaweed is a unique oceanic plant with significant protein and fiber content. Seaweed extracts contain bioactive phenolic structures^[3] — antioxidants — which is one reason seaweed is good for you. Let’s examine this in detail.

Thyroid Health

First of all, we should mention the iodine content of seaweed. Iodine is an essential trace element for our thyroid function. The thyroid gland can not synthesize thyroid hormones without iodine. Therefore iodine consumption is important for the things for which thyroid hormones are responsible, such as growth and energy metabolism.

If you don’t consume enough iodine, thyroid hormone production is affected, which may jeopardize many metabolic activities of your body. Also, the thyroid gland can attempt to overcorrect the problem, causing a goiter. Goiter disease is associated with a slower metabolism and you may gain weight, feel fatigued, or have a lower cognitive function.

The World Health Organization^[4] recommends 150 micrograms of iodine per day for adults’ optimal thyroid function. The European Commission Scientific Committee on Food indicates the tolerable upper level of iodine as 600 micrograms per day for adults and 200 micrograms per day for children. Just as important as insufficient iodine intake, excess iodine intake is also harmful to your thyroid gland and its function

Seaweed is one of the richest sources of iodine. Brown seaweed^[5] consumption affects thyroid-stimulating hormone^[5] levels and metabolism, similar to iodine supplement outcomes.

Appetite Control

Several human studies indicated that the consumption of alginate, the main polysaccharide found in seaweed, significantly impacts hunger and food intake. A study investigated^[6] the acute effect of alginate-supplemented beverages. According to individuals’ self-report, it showed regulation in appetite and reduced hunger compared to the placebo.

In another study,^[7] overweight men consumed seaweed-enriched bread, and their energy intake was reduced by 16.4 percent after four hours of consumption.

Sodium alginate^[8] is an important product for the industry due to its gelling capacity as a thickening agent. This function also can be related to satiety in the digestive tract.

Regulation Of Metabolism

Seaweed may have anti-diabetic and anti-obesity effects to lose weight, but the majority of studies on it are limited to animal studies. It suggests that a substance called fucoxanthin found in seaweed may aid weight loss. An animal study^[9] showed that fucoxanthin contributes to losing weight by increasing the expression of a fat-metabolizing protein.

Fucoxanthin^[10] has a role in blood sugar control and helps weight loss. However, it should be noted that these studies are animal studies. More human studies, such as this one^[11] from 2020, are needed to prove the effect of seaweed on obesity.

Fiber consumption increases bacterial diversity and supports gut microbiota, which is closely related to inhibiting the inflammation that leads to chronic diseases. Insulin and blood sugar levels are also regulated with fiber consumption by prolonging their digestion and mitigating their absorption. Fiber binds some fat and cholesterol in the digestive tract which enhances their excretion, thus also lowering cholesterol levels.

Immune Effects

Researchers have demonstrated in detail brown seaweed’s immune booster effect.^[12] This function of seaweed is mainly due to its polysaccharides, such as polyphenol and fucoidans; carotenoids, such as fucoxanthins; and phytosterol content.

These bioactive molecules protect intestinal epithelial cells, which constitute the intestinal wall, from harmful food substances and chemicals. When toxic substances enter the body, intestinal cells start an immune response to fight back. Seaweeds also support intestinal integrity, providing another barrier against toxic substances.

Seaweed’s biochemical structure also helps the regulation of immune response, keeping it at a favorable level to control allergic reactions.

These seaweed components have the antioxidant and anti-inflammatory capacity to reduce free radicals that cause cellular damage in the intestine and the body in general. Polyphenols are the main antioxidants that humans get from foods. This may explain the anti-cancer effects of seaweed consumption. You may wonder if seaweed is good for your skin due to its antioxidant capacity. Yes, it is possible.

These immune effects of seaweed are a great explanation for why seaweed is good for long-term health — anti-obesity, anti-inflammatory, anti-cancer, anti-fibrotic, etc.

What Is Seaweed?

Seaweeds grow using the carbon dioxide and nutrient sources in the ocean; they have very low carbon emissions and carbon footprints, important in the case of industrial production. The food industry uses seaweeds to isolate carbohydrate macromolecules such as alginate^[13] and fucoidan, proteins, polyphenols, carotenoids, and omega-3 unsaturated fatty acids. It also contains many trace metals such as iodine, potassium, magnesium, calcium, and iron.

Recent studies^[14] on seaweeds have focused on the bioactive components of aquatic foods. They have the potential to decrease risk factors for chronic diseases such as diabetes, high blood cholesterol, cancer, cardiovascular disease, or obesity.

However, there can be potential adverse effects, including too much iodine and heavy metal consumption, such as arsenic.

Scientific studies are generally focused on brown seaweed in this family. But there are also red seaweeds and green seaweeds.

Seaweed Nutritional Benefits

The nutrient content differs according to seaweed type and environmental factors, but here are the general numbers for fresh and dried seaweed according to The United States Department of Agriculture Food Data Central.

Nutrients	1 cup of Dried Seaweed 15 grams[15]	1 cup of Fresh Seaweed 80 grams[15]	Unit
Water	1	68.5	grams
Energy	44.7	32.8	kilocalories
Protein	4.77	2.81	grams
Total fat	0.601	0.392	grams
Carbohydrate	7.86	6.35	grams
Fiber	0.84	0.56	grams
Sugar	0.456	0.464	grams
Calcium, Ca	55.8	103	milligrams
Iron, Fe	3.75	1.82	milligrams
Magnesium, Mg	72.3	61.6	milligrams
Phosphorus, P	12.8	48	milligrams
Potassium, K	186	132	milligrams
Sodium, Na	86.2	307	milligrams
Zinc, Zn	0.585	0.712	milligrams
Copper, Cu	0.504	0.181	milligrams
Selenium, Se	1.1	0.56	micrograms
Vitamin C	0.75	12	milligrams

The Food Data Central didn’t provide the iodine levels of seaweeds. Still, in several studies,^[16] the iodine content of different types of seaweed is available. Nori, a commonly used seaweed in sushi, includes 36.9 micrograms of iodine per gram.

Wakame seaweed contains 139.7 micrograms of iodine per gram. Kombu seaweed even contains up to 2523.3 micrograms of iodine per gram, which is nearly 16 times the recommended dietary intake and four times the tolerable upper level — important information for those with thyroid conditions or who are on thyroid medication.

Protein

The protein content^[14] of edible seaweeds has a wide range from nearly one percent to 45 percent. Five grams of dried brown, red, and green seaweed provides protein amounts up to 1.97, 4.5, and 2.98 percent, respectively, according to Reference Nutrient Intake.

Seaweed is an excellent source of lysine amino acid, an essential amino acid. Comparatively, plant-based protein sources, such as soy, corn, rice, wheat, etc., have limited lysine levels.

Dietary Fiber

Fiber content makes seaweed a beneficial food for a healthy digestive system and metabolism.

Comprehensive research has revealed that many people don’t consume the required daily fiber. Research indicates that daily fiber intake for adults should be 25 to 35 grams per day, yet the average fiber consumption is lower than 20 grams per day around the world.^[17]

Seaweed is a high and functional fiber source. Five grams^[14] of brown, red, or green seaweed contribute to daily dietary fiber intake up to 14.28, 10.64, or 12.10 percent, respectively. But these numbers also vary according to fiber type; you can get alginate, fucoidan, and laminarin polysaccharides from brown seaweeds; carrageenan, agar, xylan, and porphyrin from red seaweeds; and xylan, ulvan, and cellulose from green seaweeds.

Are There Any Side Effects When Consuming Seaweed?

Too Much Iodine

The primary iodine source of humans is generally iodized salt, dairy products, and bread. However, high iodine concentrations are naturally found in seafood such as seaweeds. While consuming these food products, it is easy to exceed the recommended daily intake, which is 150 micrograms for adults.

Hypothyroidism or hyperthyroidism,^[18] the production of low or high levels of thyroid hormones, can result from excessive iodine consumption due to thyroid function disturbances. Too much iodine overstimulates the thyroid gland; too little causes thyroid tissue to attempt overcorrection by growing larger, i.e., a goiter.

Heavy Metals

Many essential and non-essential metals have been detected^[19] in seaweed. There are metals such as lead, cadmium, and arsenic, which are known as heavy metals, and their excess intake can cause health problems.

Due to the pollution and heavy metal concentrations in the seas, seafood may carry a risk in terms of heavy metal intake. For this reason, it may be beneficial to prefer products of reliable brands under good production conditions. The site of origin of the seaweed can make a difference in undesirable elements,

How To Eat Seaweed

Seaweed salad, dried seaweed, roasted seaweed, or seaweed snacks are good for creating variety in your diet.

Arguably, the most delicious option for consuming edible seaweeds is sushi. The outer layer of sushi consists of nori, a seaweed, and is readily available at most food stores.

• You can use the nori as the outer layer to wrap your meat and vegetable side dishes.
• You can prefer making seaweed salads for eating fresh seaweed.
• Dried seaweed can be a nice snack option with dips you can prepare with yogurt. However, since it is easy to consume too much, be careful.
• You can get a nice spice by pulverizing dried seaweeds.

How Much Seaweed To Eat Per Day?

How much seaweed you can consume is based on the amount of iodine, which varies with the type of seaweed, and possibly heavy metals if the source of the seaweed is sketchy. Considering the abovementioned amounts, consuming 16 grams of nori or four grams of wakame will not exceed your daily tolerable iodine level. But you should consider other dietary iodine sources, too.

You can request information on how much iodine per gram of seaweed you buy from the manufacturer.

The Bottom Line

Seaweed is one of the seafood products that have health benefits due to its rich content. It is an important source of bioactive compounds such as iodine and polyphenols carotenoids.

However, depending on the type and environmental conditions, it may contain very high amounts of iodine and even some heavy metals. It is a beneficial nutrient as long as the limits on consumption are observed.

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