Seaweed Nutrition Facts and Health Benefits

Seaweed, annotated

Verywell / Alexandra Shytsman

Seaweed has been popular in Asian cuisine for centuries, and it's starting to catch on in other parts of the world as well. Seaweed is a source of several vitamins and minerals, and offers several promising health benefits.

However, seaweed can also carry potential pollutants from the ocean to your plate. If you've heard mixed advice on eating seaweed, consider this nutrition information to help you decide whether to include it in your diet.

Seaweed Nutrition Facts

Two tablespoons of wakame (10g) provide 4.5 calories, 0.3g of protein, 0.9g of carbohydrates, and 0g of fat. Seaweed is a good source of magnesium, calcium, and iron. The following nutrition information is provided by the USDA.

  • 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

Carbs

There is a little less than 1 gram of carbohydrate in 2 tbsp of raw seaweed. Of this, less than 1 gram comes from fiber and sugar combined. Seaweed contains various polysaccharides that act as antioxidants, providing numerous health benefits.

Fats

Raw seaweed is virtually fat-free.

Protein

A 2 tbsp serving of raw seaweed provides 0.3 grams of protein.

Vitamins and Minerals

Seaweed is rich in several vitamins and minerals, including calcium, potassium, vitamin C, folate, beta carotene, and vitamin K.

The sodium content of seaweed varies based on the brand and preparation method, but can be up to 698 milligrams per cup (raw). The 2020-2025 Dietary Guidelines for Americans suggest that most adults consume less than 2,300 milligrams of sodium daily.

Some species of edible seaweeds also provide vitamin D and B12, two essential nutrients that can be hard to come by in plant foods. Seaweed is also a good source of iodine.

Calories

Two tablespoons of wakame (10g) provide 4.5 calories, 67% of which come from carbs, 22% from protein, and 11% from fat.

Summary

Seaweed is a low-calorie, highly nutritious food that provides nutrients not often found in plant food, such as iodine, B12, and vitamin D. Seaweed is also a good source of calcium, folate, and magnesium.

Is Seaweed Good for You? Health Benefits

In addition to vitamins and minerals that may be especially valuable for vegans and vegetarians, seaweed provides unique plant compounds that have been linked to good health and disease prevention. It's also low in calories, fat, and sugar, which many people may limit in their diet to promote better health.

May Protect Against Asthma

Data reviewing the 2013–2016 Korea National Health and Nutrition Examination Survey (KNHANES) discovered that lower intakes of seaweed and seafood were associated with higher asthma rates.

Because asthma is an inflammatory disease, it's hypothesized that the polyunsaturated fats and vitamins found in these foods are protective. Although more research is needed to confirm a cause and effect benefit, introducing seaweed during pregnancy and early childhood appears to be beneficial.

Reduces Risk of Osteoporosis

Oxidation from free radicals is associated with a host of health issues, including osteoporosis (bone loss). Seaweed contains antioxidant compounds, called fucoidans, which have been shown to prevent bone breakdown by free radicals.

Specifically, fucoidans protect osteoblasts (the cells responsible for building bone) against the cell death that may otherwise be induced by oxidative stress. Seaweed also provides vitamin K and calcium, two key nutrients for bone strength.

May Aid Cancer Prevention

The fucoidans in seaweed have also been studied for cancer prevention. While human clinical trials are limited, fucoidan's ability to influence cell death shows promise as a potential supplement to traditional cancer treatments.

Like other vegetables, seaweed is also a source of antioxidants (like vitamin C and beta carotene). These compounds are known for cancer prevention qualities, especially when consumed as part of a nutrient-dense eating plan (rather than as supplements).

Promotes Heart Health

Seaweed is a good source of soluble fiber. Dulse seaweed and kombu provide 3 to 4 grams per serving. Soluble fiber binds to cholesterol, pulling it out of the body through waste. In addition to reducing cholesterol, seaweed can also help lower blood pressure levels due to its potassium content (just watch out for added sodium).

Finally, the folate in seaweed keeps homocysteine levels (a sign of inflammation) down, reducing the risk of stroke.

Supports Weight Loss

The main form of soluble fiber found in seaweed is alginate. Studies show that alginate improves satiety by delaying gastric emptying, which can reduce subsequent food intake.

Additionally, seaweed contains protein, which is also known to produce feelings of fullness. Seaweed offers ample nutrients and flavor for a minimal number of calories. Seaweed wraps, soups, or salads can be a good choice to help keep hunger pangs at bay while trying to lose weight.

Allergies

Allergies exclusively to seaweed are not commonly reported, but they are possible. Shellfish allergies and iodine allergies are more likely to occur. Shellfish allergies can be very dangerous, so caution around any possible source of cross-contamination (including seaweed) is advised.

If you are sensitive to iodine, the natural iodine content of seaweed could be a trigger. Speak to an allergist if you suspect that you have a seaweed allergy.

Adverse Effects

In addition to allergic reactions, seaweed may cause or worsen other adverse health effects.

Drug Interactions

As a natural source of vitamin K, seaweed may interfere with the anticoagulant effects of blood thinners like Coumadin (warfarin). Maintaining a consistent intake of foods high in vitamin K will help your doctor determine the correct dosage of medication for you.

Heavy Metal Content

Depending on where seaweed is sourced, it may contain high levels of heavy metals like mercury and arsenic. Varying the types of seaweed you eat, avoiding hijiki seaweed (which is known to be high in arsenic), and limiting your intake to three times per week can help you reduce heavy metal exposure from seaweed. Many U.S.-based companies test for heavy metals, so check on the label for testing.

Thyroid Problems

Because seaweed is high in iodine, people who have a history of thyroid issues should monitor their intake of seaweed. Studies have found that excess iodine consumption can lead to hyperthyroidism.

Autoimmune Disorders

Brown seaweed, in particular, has been used throughout Asian countries and boasts many health benefits. However, people who have been diagnosed with the autoimmune disorder Graves' disease should avoid seaweed because of its iodine content. Seaweed may worsen hyperthyroidism symptoms in people with autoimmune disorders.

Varieties

There are many different color variations of edible seaweed that come from different species. Nori, or purple laver, is a dark-colored seaweed used to wrap sushi. This is one of the most nutritious types of seaweed, with a high protein and nutrient content. Aonori, or green laver, is cultivated in Japan and sometimes referred to as "sea lettuce."

Kombu (in Japan) and haidai (in China) is another type of dried seaweed. A type of red algae with leathery fronds is called dulse. Dulse is commonly chewed as a raw snack in Ireland or cooked with potatoes. Other edible variations of seaweed include winged kelp, Irish moss, sea grapes, mozuku, and hiziki.

When It's Best

Seaweed can be eaten raw or dried, depending on the variety. You may be able to find more popular varieties, like nori, in your local supermarket, but other types of seaweed can be harder to find. Asian grocery stores are likely to offer a fuller selection.

Storage and Food Safety

Fresh seaweed should be handled the same way other leafy greens are handled. Wash fresh seaweed under running water before consuming or preparing. Store fresh seaweed in the refrigerator.

Dried seaweed should be placed in an airtight container after opening. Follow the expiration dates listed on the package for maximum freshness. Looking for a reputable food company online or at the grocery store will help you avoid heavy metals and other toxins.

How to Prepare

The easiest way to eat seaweed is by using dried seaweed wrapper (nori), the kind you find in sushi restaurants. Use it to wrap almost anything. You can also break dried seaweed into pieces and sprinkle the flakes onto a salad or other dishes for a nutritional boost. Seaweed is also popular in Asian soups, such as miso soup.

15 Sources
Verywell Fit uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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By Mark Stibich, PhD
Mark Stibich, PhD, FIDSA, is a behavior change expert with experience helping individuals make lasting lifestyle improvements.