7 Surprising Health Benefits of Eating Seaweed

1. Contains iodine and tyrosine, which support thyroid function

Your thyroid gland releases hormones to help control growth, energy production, reproduction and the repair of damaged cells in your body.

Your thyroid relies on iodine to make hormones. Without enough iodine, you may start to experience symptoms like weight changes, fatigue, or swelling of the neck over time.

The daily value (DV) of iodine for adults is 150 mcg per day.

Seaweed has the unique ability to absorb concentrated amounts of iodine from the ocean.

Its iodine content varies greatly depending on the type, where it was grown, and how it was processed. In fact, one dried sheet of seaweed can contain between 16 mcg per gram and 2,984 mcg/g, or 11–1,989% of the DV.

Below is the average iodine content of three different dried seaweeds:

• Nori: 37 mcg per gram (25% of the DV)
• Wakame: 139 mcg per gram (93% of the DV)
• Kombu: 2523 mcg per gram (1,682% of the DV)

Kelp (kombu) is one of the best sources of iodine.

Seaweed also contains an amino acid called tyrosine, which is used alongside iodine to make two key hormones that help the thyroid gland do its job properly.

2. Good source of vitamins and minerals

Each type of seaweed has a unique set of nutrients.

Sprinkling some dried seaweed on your food not only adds taste, texture, and flavor to your meal, but it’s an easy way to boost your intake of vitamins and minerals.

Generally, 1 tablespoon (7 grams) of dried spirulina can provide:

• Calories: 20
• Carbs: 1.7 grams
• Protein: 4 grams
• Fat: 0.5 gram
• Fiber: 0.3 grams
• Riboflavin: 20% daily value (DV)
• Thiamin: 14% DV
• Iron: 11% DV
• Manganese: 6% DV
• Copper: 47% DV

Seaweed also contains small amounts of vitamins A, C, E, and K, along with folate, zinc, sodium, calcium, and magnesium.

While it may only contribute to a small percentage of some of the DVs above, using it as a seasoning once or twice per week can be an easy way to add more nutrients to your diet.

The proteins present in some seaweeds, such as spirulina and chlorella, contain all of the essential amino acids. This means seaweed can help ensure you get the full range of amino acids.

Seaweed can also be a good source of omega-3 fats and vitamin B12.

It appears that dried green and purple seaweed contain substantial amounts of vitamin B12. One study found 2.4 mcg or 100% of the RDI of vitamin B12 in 4 to 8 grams of nori seaweed.

That said, there is an ongoing debate about whether your body can absorb and use the vitamin B12 from seaweed.

3. Contains a variety of protective antioxidants

Antioxidants can make unstable substances in your body called free radicals less reactive.

This makes them less likely to damage your cells.

Furthermore, excess free radical production is considered to be an underlying cause of several diseases, such as heart disease and diabetes.

In addition to containing the antioxidant vitamins A, C, and E, seaweed boasts a wide variety of beneficial plant compounds, including flavonoids and carotenoids. These have been shown to protect your body’s cells from free radical damage.

A lot of research has focused on one particular carotenoid called fucoxanthin.

It’s the main carotenoid found in brown algae, such as wakame, and it has 13.5 times the antioxidant capacity of vitamin E.

While the body does not always absorb fucoxanthin well, absorption may be improved by consuming it along with fat.

Nevertheless, seaweed contains a wide variety of plant compounds that work together to have strong antioxidant effects.

4. Provides fiber and polysaccharides that can support your gut health

Gut bacteria play an enormous role in your health.

It’s estimated that you have more bacteria cells in your body than human cells.

An imbalance in these “good” and “bad” gut bacteria can lead to sickness and disease.

Seaweed is an excellent source of fiber, which is known to promote gut health.

It can make up about 35% to 60% of seaweed’s dry weight. This is higher than the fiber content of most fruits and vegetables.

Fiber can resist digestion and be used as a food source for bacteria in your large intestine instead.

Additionally, particular sugars found in seaweed called sulfated polysaccharides have been shown to increase the growth of “good” gut bacteria.

These polysaccharides can also increase the production of short-chain fatty acids (SCFA), which provide support and nourishment to the cells lining your gut.

5. May help you lose weight by delaying hunger and reducing weight

Seaweed contains a lot of fiber, which is believed to provide little to no calories.

The fiber in seaweed may slow stomach emptying, too. This helps you feel fuller for longer and can delay hunger pangs.

Seaweed is also considered to have anti-obesity effects. In particular, animal studies suggest that a substance in seaweed called fucoxanthin may help reduce body fat.

A 2019 study showed that obese mice lost weight when fed powdered algae with high fucoxanthin content for 6 weeks.

Although the results in animal studies appear very promising, it’s important that human studies are conducted to verify these findings.

In a 2023 clinical trial of 28 patients with metabolic syndrome, fucoxanthin was found to reduce body weight, blood pressure, and triglyceride levels. Further human studies are needed.

6. May reduce heart disease risk

Heart disease is the leading cause of death worldwide.

Factors that increase your risk include high cholesterol, high blood pressure, smoking, and being physically inactive or overweight.

Seaweed may help reduce your blood cholesterol levels.

A 2023 meta-analysis found that brown seaweed intake significantly decreased the levels of total cholesterol and LDL.

Heart disease can also be caused by excessive blood clotting. Seaweed contains carbohydrates called fucans, which may help prevent blood from clotting.

In fact, one animal study found that fucans extracted from seaweed prevented blood clotting as effectively as an anti-clotting drug.

Researchers are also starting to look at peptides in seaweed. Initial studies in animals indicate that these protein-like structures may block part of a pathway that increases blood pressure in your body.

However, large-scale human studies are required to confirm these results.

7. May help reduce your risk of type 2 diabetes by improving blood sugar management

Diabetes occurs when your body is unable to balance your blood sugar levels over time.

By the year 2030, 643 million people worldwide are expected to have type 1 or type 2 diabetes, with the estimate rising to 783 million by 2045.

Interestingly, seaweed has become a research focus for new ways to support people who are at risk of diabetes.

An 8-week study of 60 Japanese people revealed that fucoxanthin, a substance in brown seaweed, may help improve blood sugar control.

Participants received a local seaweed oil that contained either 0 mg, 1 mg, or 2 mg of fucoxanthin. The study found that those who received 2 mg of fucoxanthin had improved blood sugar levels compared to the group who received 0 mg.

The study also noted additional improvements in blood sugar levels in those with a genetic disposition to insulin resistance, which usually accompanies type 2 diabetes.

What’s more, another substance in seaweed called alginate prevented blood sugar spikes in animals after they were fed a high-sugar meal. It’s thought that alginate may reduce the absorption of sugar into the bloodstream.

A 2023 meta-analysis found that brown seaweed consumption significantly improved postprandial blood glucose, glycated hemoglobin (HbA1c), and Homeostatic Model Assessment of Insulin Resistance (HOMA-IR).

Possible dangers of seaweed

Although seaweed is considered a healthy food, there may be some potential dangers to consuming too much.

Excess iodine

Seaweed can contain a very large and potentially dangerous amount of iodine.

Japanese people’s high seaweed intake might be one reason why they have the highest life expectancy in the world.

However, the daily average intake of iodine in Japan is estimated to be 1,000–3,000 mcg (667–2,000% of the RDI). This poses a risk to those who consume seaweed every day, as 1,100 mcg of iodine is the tolerable upper limit (TUL) for adults.

Fortunately, in Asian cultures, seaweed is commonly eaten with foods that can inhibit the uptake of iodine by the thyroid gland. These foods are known as goitrogens and are found in foods like broccoli, cabbage, and bok choy.

Additionally, it’s important to note that seaweed is water-soluble, which means cooking and processing it can affect its iodine content. For example, when kelp is boiled for 15 minutes, it can lose up to 99% of its iodine content.

While a few case reports have associated iodine-containing kelp consumption and thyroid dysfunction, thyroid function returned to regular once consumption stopped.

Nevertheless, high amounts of seaweed can affect thyroid function, and symptoms of too much iodine are often the same as symptoms of not enough iodine.

If you think you are consuming too much iodine and experience symptoms like swelling around your neck region or weight fluctuations, reduce your intake of iodine-rich foods and talk with your doctor.

Heavy metal load

Seaweed can absorb and store minerals in concentrated amounts.

This poses a health risk, as seaweed can also contain large amounts of toxic heavy metals such as cadmium, mercury, and lead.

That said, the heavy metal content in seaweed is usually below the maximum concentration allowances in most countries.

A 2017 study analyzed the concentration of 20 metals in 8 different seaweeds from Asia and Europe. It found that the levels of cadmium, aluminum, and lead in 4 grams of each seaweed did not pose any serious health risks.

Nonetheless, if you consume seaweed regularly, there is the potential for heavy metals to accumulate in your body over time.

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

The bottom line

Seaweed is an increasingly popular ingredient in cuisines all over the world.

It’s the best dietary source of iodine, which helps support your thyroid gland.

It also contains other vitamins and minerals, such as vitamin K, B vitamins, zinc, and iron, along with antioxidants that help protect your cells from damage.

However, too much iodine from seaweed could harm your thyroid function.

For optimum health benefits, enjoy this ancient ingredient in regular but small amounts.