The Health Benefits of Kombu

Kombu: Health Benefits, Side Effects, Storage, and Preparation

Kombu

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Kombu is a subvariety of kelp, a brown sea algae otherwise known as seaweed or sea vegetable. It belongs to the group of brown seaweeds referred to as Laminariacea and has many species including Laminaria japonica, Laminaria ochroleuca, and Saccharina Latissima, to name a few.

Seaweed, like kombu, has been consumed in various parts of the world, particularly in the far east for many centuries and for good reason. It has been linked to health and longevity. Naturally rich in antioxidants, vitamins, minerals, and healthy fats, kombu provides plenty of health benefits. Mostly available fresh or dried, it can also be used in powdered form. Kombu is traditionally used for soup stocks, salads, and even fertilizer and hair dye.

Health Benefits

Rich in Vitamins

Kombu is a low calorie, nutrient dense food. One seven-inch piece of kombu contains roughly 10 calories, 0 grams fat, 0 grams cholesterol, 180 milligrams (mg) sodium, 340 mg potassium, 2 grams carbohydrate, 2 grams fiber, 4 percent calcium, and 12 percent magnesium. It also contains vitamin C, A, E, K, B-vitamins, iodine, iron, magnesium, manganese, and copper.

This combination of vitamins and minerals makes kombu a nutrition powerhouse, chock full of antioxidants, which also boosts immunity.

A Great Source of Iodine

Iodine is a critical component of thyroid hormones. It is also important in brain development and, therefore, an important nutrient for women who are pregnant or breastfeeding.

According to registered dietician and culinary nutritionist Kristy Del Coro, “Seaweed is one of the richest plant-based sources of iodine, which is an essential micronutrient, and often under-consumed, particularly among pregnant women.” Seaweed is a great alternative to iodized salt—a major iodine source in the Western diet—because it contains less sodium.

Consult With Your Doctor

However, if you are pregnant it’s important to discuss seaweed consumption with your physician because some varieties of kombu have a California warning label that states: “Consuming this product can expose you to chemicals, including lead, which is known to the State of California to cause cancer and birth defects or other reproductive harm.”

This may sound alarming, but the California Prop 65 warnings are oftentimes considered a right-to-know disclaimer. According to the American Cancer Society, “Scientists classify all of these cancer-related substances at least as probable carcinogens, meaning that they might cause cancer in some people. But not all of them are known carcinogens (known to cause cancer) by groups and experts outside the state of California. This means that not every compound labeled as a possible cancer-causing substance has been proven to the worldwide scientific community to actually cause cancer.”

The warning is to let consumers know about the presence of a substance.

Nonetheless, this is a confusing label. In order to make an informed decision, it’s a good idea to get more educated and ask your physician for their medical expertise. For more information go to www.P65Warnings.ca.gov/food.

Rich in Filling Fiber

A diet rich in fiber has been associated with a healthier weight, better blood sugar control, and decreased risk of cardiovascular disease. Seaweed contains dietary fiber, mostly soluble, which may help lower cholesterol and increases feelings of fullness.

The amount of fiber will range depending on the amount eaten, but typically one seven-inch piece contains about 2 grams of fiber. One snack-pack (depending on the brand), which contains about ten super thin sheets, contains 1 gram of fiber or 4 percent of the daily recommended value.

Plant-Based Omega 3 Fatty Acids

Omega 3 fatty acids, eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA), are important for brain health and development, act as an anti-inflammatory agent, and can also help to decrease triglycerides (a type of fat in the blood). EPA and DHA are typically found in the flesh of fish, but kombu serves as a plant-based type of omega-3 fatty acid.

In fact, of all algae varieties, kombu provides the highest amounts of both EPA and DHA.

Some studies suggest that fermented forms of Laminaria japonica may improve short term memory in the elderly.

Antioxidants

You may have heard of kombu, referred to as “a treasure of the sea,” by some researchers due to its versatile effects such as its antioxidant properties. Laminaria japonica is particularly rich in fucoxanthin, a type of carotenoid. Researchers reviewed the benefits of fucoxanthin and believe that this carotenoid has great potential in the prevention or management of MS, obesity, and other chronic diseases.

The issue that there is little information using human clinical trials and most of the studies have been conducted on animals. More research is needed to discover dosages and long-term use. Until then, unless contraindicated, dietary consumption of kombu should be encouraged. 

It Contains Fucoidan

Kombu contains a type of marine acid polysaccharide knows as fucoidan. A polysaccharide is a long chain carbohydrate made of up of smaller carbohydrate monosaccharides. These types of compounds are typically used by our bodies for energy or to help with cellular structure. In a review published in Marine Drugs, scientists discuss the host of benefits fucoidan provides, including its ability to have anticancer (cancer prevention), antioxidant, anti-inflammatory, immunoregulatory (boosting the immune system) properties.

Additionally, research suggests that fucoidan could have antiviral properties, aiding in healing viral infections and shortening the length of the disease. Animal studies suggest the beneficial effects on fucoidan on gut health, promoting healthy gut bacteria, which can improve digestion and reduce gas.

Animal studies have also found a relationship in reduction of metabolic syndrome and the treatment of obesity. More specifically, fucoidan has been shown to reduce lipogenesis (fat storage) and increase the breakdown of fat (lipolysis). Keep in mind that these studies are conducted on animals and more research is indicated to determine its effects on humans.

Other Health Claims

Some preparations of kombu will make statements that kombu can reduce the risk of diabetes and help improve arthritis. Since kombu is rich in fiber and contains antioxidants this could be true, but these claims are not approved by the Food and Drug Administration (FDA). While no single food can cure anything, adding seaweed to your diet can certainly boost your nutrition.

What to Look For

You can find kombu in specialty markets, in the Asian food section in regular supermarkets, and online (websites like Amazon sell it). Depending on what you are using seaweed for, you can purchase it fresh or dried. Del Coro educates us on how it is made. She says, “Even when consumed ‘fresh’ it may have originally been dried and reconstituted in water. For example, kelp varieties are typically dried into sheets and then soaked in water before being eaten in a salad or added to soups and stocks as seasoning. Because of the natural sodium in seaweed, some canned beans will even use kombu instead of salt.”

For example, the company Eden keeps its beans preserved without added sodium and instead uses kombu seaweed.

When possible, it’s probably best to purchase organic kombu to ensure fewer chemical residues and less chance of adulteration. Most varieties of kombu are good choices. The key is to look for items that, “do not contain a large amount of added salt on top of its naturally containing sodium,” states Del Coro.

For example, look for snack packs that contain no added sea salt. If they do have some, make sure it’s labeled as the last ingredient for a lower sodium product. 

Dosage

There is no set dosage of kombu. However, a typical serving size for use in recipes is about one dried sheet. Or, if you are using powdered formula, follow the serving size recommendations.

Preparation and Storage

Kombu is an essential ingredient used in the Japanese noodle broth dashi but can be added to vegetables, soups, stocks, grains, beans, or stew dishes. It can also be pickled or deep fried. Pan or oven roast it and grind it into a powder and use it as a nutritious condiment on popcorn, or as a sandwich topper or salad ingredient.

When cooking with kombu, add a small piece to soups, stewed vegetables, and grains as they cook.

Remove the kombu when the recipe is complete—the nutrition will have seeped out into your meal. Note: if you boil or steam seaweed in an uncovered pot and discard the water you will lose much of the vitamins and minerals.

Store dried kombu in an airtight container in a cool, dry place. Doing so can keep your kombu fresh for several years. Package labels tell consumers not to store wet sea vegetables; wet conditions may grow mold or deteriorate. You can also look for canned beans that use kombu as a preservative as compared to salt.

Side Effects

It is uncommon to develop any side effects, such as nutrient toxicity, from kombu. However, because kombu is so high in iodine, iodine toxicity can occur if you eat large amounts. Children are more susceptible. Signs and symptoms of iodine toxicity include:

  • Abdominal pain
  • Coughing
  • Delirium
  • Diarrhea
  • Fever
  • Gum and tooth soreness
  • Loss of appetite
  • Metallic taste in mouth
  • No urine output
  • Rash
  • Salivation
  • Seizure
  • Shock
  • Shortness of breath
  • Stupor
  • Thirst
  • Vomiting

If you experience any of these symptoms you should contact your physician immediately.

Contraindications

For people who are allergic to fish or shellfish, kombu may not be appropriate as varieties may have traces of fish or shellfish. In addition, for those people on thyroid or potassium medication/supplements, seaweed can be problematic as it contains iodine and potassium which can interfere with thyroid hormone levels or blood levels of potassium. Discuss with your healthcare provider before consuming kombu.

Common Questions

What are the differences between types of seaweed and how are they eaten? 

Kombu is one of many types of seaweed varieties. Some other types are red, green, and brown. Del Coro says, “Dulse, nori and the thickeners agar and carrageenan are red algae, chlorella is green, and kelp is brown. While, arame, wakame, and kombu are actually subvarieties of kelp.”

What type of seaweed is in the seaweed salad served at Asian restaurants? 

“The seaweed found in seaweed salads served as side dishes in Asian cuisine are usually combinations of green and brown varieties that have been rehydrated. Nori, however, is dried and used in sheets commonly used to wrap sushi and found packaged in grocery stores as a snack food,” says Del Coro.

Can I eat kombu if I am on a blood thinner?

Seaweed contains vitamin K which plays a role in blood clotting. If you take a blood thinner, it’s important to keep your intake of vitamin K foods consistent for your medication to work properly. If you are taking a blood thinner, it may be a good idea to consult with your physician before including seaweed into your diet.

If kombu is so healthy for me, then why do certain varieties have a California Warning Label about the possibilities of exposure to heavy metals?

California’s Proposition 65, also called the Safe Drinking Water and Toxic Enforcement Act, was enacted in 1986. It was developed to help the people of California make informed decisions about protecting themselves from chemicals known to cause cancer, birth defects, or other reproductive harm. Some people refer to this proposition as more of a “right to know.”

This is complicated. In order to find out what substance is in the product, how you might be exposed to it, and what level of risk it poses, you need to delve further to find out more information. You’ll want to research the product and contact the manufacturer to find out what substance the product contains and decide whether or not you should consume it. For example, the only time a company does not have to issue the warning is if a person exposed to the substance at the expected level for 70 years is estimated to have a one in 100,000 chance or less of getting cancer due to that exposure.

The strict guidelines are similar for birth defects and reproductive issues. This is important because the California Prop 65 states that a warning “does not necessarily mean a product is in violation of any product-safety standards or requirements.” They must list it even if there are trace amounts and it poses no risk.

Keep in mind that the federal United States Food and Drug Administration regulates all food, and they have not issued a warning about seaweed. So, it is probably safe to say that the levels of exposure are not significant. However, its always prudent to make an informed decision before consumption, especially if you are an at-risk population, such as a young woman or man of reproductive age, if you are pregnant, or if you have an increased risk of cancer.

A Word From Verywell

Kombu, a type of brown seaweed, is a nutrient-packed, natural superfood that has been used in far east cultures for centuries. It’s chock full of vitamins, minerals, fiber, healthy fats, and powerful antioxidants. Animal studies have measured its potential benefits in disease prevention. Use kombu as a snack, as a sandwich topper, in salads, soups, stews, or beans—the options are endless.

For those with thyroid disease or those taking thyroid or potassium supplements/medicine, are pregnant, or have an increased risk of cancer, contact your healthcare provider before consumption.

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Article Sources

Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial policy to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  • American Cancer Society. Cancer Warning Labels Based on California’s Proposition 65.

  • D'Orazio, N, et. al. Fucoxantin: A Treasure from the Sea. Mar Drugs. 2012 Mar; 10(3): 604–616. DOI: 10.3390/md10030604

  • National Institute of Health. Iodine poisoning.

  • Reid, SNS, et. al. The Effects of Fermented Laminaria japonica on Short-Term Working Memory and Physical Fitness in the Elderly. Evid Based Complement Alternat Med. 2018 Jun 12;2018:8109621. DOI: 10.1155/2018/8109621.

  • Vishchuk, OS, et. al. Sulfated polysaccharides from brown seaweeds Saccharina japonica and Undaria pinnatifida: isolation, structural characteristics, and antitumor activity. Carbohydr Res. 2011 Dec 13;346(17):2769-76. doi: 10.1016/j.carres.2011.09.034.

  • Xing, M. et. Al. Biological activities of fucoidan and the factors mediating its therapeutic effects: a review of recent studies. Mar. Drugs 2019, 17(3), 183; DOI: 10.3390/md17030183