Kombu Nutrition Facts and Health Benefits

kombu-seaweed-kelp

 Rodrigo Ruiz Ciancia / Getty Images

Kombu is kelp, an edible sea vegetable that belongs to a group of brown seaweeds called laminariaceae. Kombu is most commonly used to make dashi—a Japanese soup stock that has a delicate umami flavor—sometimes referred to as the fifth taste. Kombu is one of the three most common seaweed varieties in Japan and is commonly grown in Japan and Korea. There are several different kinds of kombu, each with a slightly different taste.

Like most seaweed, kombu is considered to be good for your body and good for the environment. However, there are concerns about kombu consumption contributing to iodine toxicity that consumers should be aware of.

Nutrition Facts

The following nutrition information is provided by the USDA for 1/4 cup (7g) serving of kombu.

  • Calories: 17
  • Fat: <0g
  • Sodium: 161mg
  • Carbohydrates: 3g
  • Fiber: 1g
  • Sugars: 0g
  • Protein: 1g

Carbs

Most of the calories in kombu come from carbohydrates. But since kombu is low in calories, you won't significantly increase your carb intake when you eat it. A typical 1/4 cup serving provides only 3g of carbs. Most of the carbohydrate is starch, but you'll also benefit from a small amount of fiber in a single serving.

The estimated glycemic load of kombu is zero if your serving size is 1/4 cup. Even if you increase your serving size to a full ounce (28g) the glycemic load only increases to one.

Fats

There are only trace amounts of fat in kombu. A single 1/4 cup serving provides almost zero grams. Also, kombu is commonly served in dishes (such as dashi) that are traditionally low in fat. However, preparation methods and ingredients vary and can change the fat content.

Protein

Kombu can slightly boost the protein content of your favorite soup, salad or dish, depending on how much you use. A small serving provides less than 1 gram of protein.

Micronutrients

Kombu is an excellent source of iodine, in fact, it has the highest iodine content compared to other popular types of seaweed (nori and wakame). But the iodine content varies depending on the species. According to a published report that evaluated the iodine content of various types of kombu, 10 different species were found to average 1,542 micrograms per gram when dried. As a basis for comparison, wakame provides 420 micrograms of iodine per gram.

Other minerals in kombu include zinc, copper, manganese, magnesium, iron, and calcium.

Kombu also provides vitamins. Each 2-tablespoon serving provides 5% of your recommended daily intake of folate and 8% of your daily recommended intake of vitamin K. Kombu also provides small amounts of vitamin C, riboflavin, and pantothenic acid (also known as vitamin B5).

Health Benefits

Kombu and other forms of seaweed are promoted as providing a number of health benefits and nutritional advantages. For example, researchers know that seaweed can provide a relatively inexpensive and environmentally-friendly combination of high-quality protein, healthy fats, fiber, and other nutrients. Therefore, there may be opportunities to manufacture seaweed-based functional foods to reduce the risk for cardiovascular disease and provide other health advantages around the world. 

But researchers have also reported that there remain substantial challenges in fully understanding the health benefits and balancing those with potentially adverse effects. Moreover, there is wide variability in the nutritional content and bioavailability of seaweed, based on factors including where it comes from and how it is manufactured and prepared. For these reasons, it remains unclear whether or not seaweed can live up to the superfood claims that are sometimes promoted in the media and by seaweed sellers.

There are other areas of investigation relating to the potential medicinal benefits of kombu and other types of seaweed. For example, some researchers are trying to understand its role in the possible prevention of breast cancer. Early studies have shown that a higher intake of seaweed may provide a protective effect against the disease. But right now, the studies have been small and limited in scope.

Another area of interest is in a seaweed ingredient called fucoxanthin. Fucoxanthin is a carotenoid that provides antioxidant benefits and is being investigated for its antiobesity, antitumor, anti-diabetes, anti-inflammatory, and both cardiovascular and cerebrovascular protective effects. Some believe it may also benefit the liver. 

However, research investigating these benefits is still in the early stages. Even the researchers who are investigating the links between seaweed consumption and health outcomes acknowledge that there are not enough human studies to confirm these benefits.

Iodine Benefits and Risks

The iodine in kombu can boost your health. According to the National Institutes of Health, iodine is needed to make thyroid hormones in the body. Thyroid hormones help regulate your metabolism and are essential for bone and brain development during pregnancy and infancy. If you don’t get enough iodine, a goiter (an enlarged thyroid gland) may develop and is often the first sign of hypothyroidism.

But it is also possible to get too much iodine. If you consume too much iodine on a regular basis, thyroid hormone synthesis is inhibited. The NIH warns that too much iodine can cause the same symptoms as iodine deficiency including goiter, elevated TSH levels, and hypothyroidism.

U.S.health officials have established the upper limit for adults at 1,100 micrograms of iodine per day. One gram of raw dried kombu provides 1,542 micrograms of iodine. Cooking kombu reduces its iodine content.

Studies have shown that iodine levels among Japanese people who consume nori, wakame, and kombu is estimated to average 1,000-3,000 micrograms per day. Some health experts associate the higher iodine intake with health benefits seen in Japanese populations including a longer average life expectancy, a lower risk for certain types of cancer, and fewer heart-related deaths in men and women aged 35-74 years.

Common Questions

What does kombu taste like?

Many people say that kombu tastes like mushrooms with a slight briny edge.

Kombu contains glutamic acids, which are the basis for umami—the fifth taste. Before the discovery of umami by the Umami International Symposium in Hawaii, the four tastes were defined as sour, salty, sweet, and bitter. This fifth taste is described as being pleasantly savory.

What is the white powder on kombu? Should I wash it off?

You should probably not wash off the white powder. Called mannitol, it is a distinctive characteristic of kombu and provides its flavor. If you prefer less of it, you can wipe dry kombu down with a wet towel.

How does kombu compare to other types of seaweed?

In terms of taste, wakame seaweed is sweeter and nori is usually considered to have a much stronger taste profile than kombu.

Nutritionally, kombu has the highest iodine content while nori and wakame have lower iodine contents. But even among these three popular varieties, the nutritional content including the iodine content can vary depending on species, harvest location, and preparation.

Can you eat kombu that you find on the beach?

Fresh seaweed harvesting has gained popularity, even in the United States where the west coast yields several types that have a similar taste profile to kombu. While you might be able to eat seaweed that you harvest on the beach, it is not always recommended simply because there is no way of knowing if the sea vegetable has been exposed to pollutants or other contaminants.

Does boiling seaweed change its nutritional profile? 

Cooking seaweed substantially reduces its iodine content, which might make it safer to consume on a regular basis.

According to at least one study, boiling kombu reduces its iodine content by 99%.

But you may also eat more seaweed after it has been boiled because texture softens, making it easier to consume. 

Is a seaweed supplement just as healthy as eating seaweed?

For those that don't like the taste or texture of kombu or other types of seaweed, supplements are available. However, there isn't strong evidence to show any benefit. And there may be cause for concern. Researchers have noted that there is very little legislation requiring food or supplement companies to disclose mineral, heavy metal, or iodine content of seaweed products or to provide guidance on a safe portion size of certain whole seaweeds in order to prevent excessive intakes.

If you are interested in gaining the potential health benefits of kombu, it's best to eat the food in its whole natural form. This allows you to consume both the fiber and protein it provides, along with vitamins and minerals.

Can seaweed help me lose weight?

You’ll see reports in magazines and online about the weight loss benefits of seaweed. However, there is very little evidence to support the claims.

Seaweed does contain some fiber which can help you to feel full and satisfied after eating, but human studies have not found that seaweed can provide any special benefit when you are trying to lose weight.

Recipes and Preparation Tips

You can buy kombu as a dried product, pickled in vinegar, or shredded. It is usually cooked before consuming. Kombu can be added to soups, stews, salads, or used to soften beans for easier digestion.

Kombu is most widely used in recipes for dashi, or traditional Japanese stock. There are different types of dashi, but to make the most basic variety, you simply combine three ingredients.

First, combine a small piece of dried kombu and warm water in a pot and heat just to boiling. Remove the kombu just as the water starts to boil. Then add katsuobushi or bonito flakes. These are thin shavings of the bonito fish. Simmer for 2–3 minutes, then let steep for as long as desired to enhance the flavor.

This variation of dashi (katsuo-dashi) is only one variety of the stock. You can also add mushrooms, sardines, anchovies, or other ingredients to change the flavor.

Dashi is the basis for miso soup. But there are other ways to use it. You can poach eggs in dashi, use it in vinaigrettes, or use it as a brine. Simply use the stock the way you might use any other kind of stock in your cooking.

Allergies and Interventions

According to the American Academy of Allergy, Asthma, and Immunology, there are rare cases of seaweed allergy. However, there have been published reports of individuals stating that iodine-rich foods such as kombu, may cause a skin rash or other reactions in sensitized individuals.

Those with seafood allergies may be concerned about consuming seaweed or other sea vegetables like kombu. These foods do not contain fish protein which generally causes an allergic reaction in sensitive individuals. But experts still advise caution when trying seaweed for the first time.

Iodine may interact with certain medications including methimazole (an anti-thyroid medication), medicines for high blood pressure or potassium-sparing diuretics. If you consider an iodine supplement that contains kombu or if you consume kombu regularly, speak to your healthcare provider to get personalized advice regarding potential interactions.

Lastly, keep in mind that the FDA does not require food labels to list iodine content on a food label unless a food has been fortified with this nutrient. Kombu contains iodine naturally so it would not need to be disclosed. Therefore, it will be hard to assess your iodine intake when you consume the sea vegetable. Consider cooking the food before eating it. And if you notice signs or symptoms of excess iodine intake, such as burning of the mouth, throat, and stomach or a fever, stomach pain, nausea, vomiting, diarrhea, or weak pulse consult your healthcare provider.

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