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Food as Medicine: Wakame Seaweed (Undaria pinnatifida, Alariaceae)

Editor’s Note: Each month, HerbalEGram highlights a conventional food and briefly explores its history, traditional uses, nutritional profile, and modern medicinal research. We also feature a nutritious recipe for an easy-to-prepare dish with each article to encourage readers to experience the extensive benefits of these whole foods. With this series, we hope our readers will gain a new appreciation for the foods they see at the supermarket and frequently include in their diets. We would like to acknowledge ABC Chief Science Officer Stefan Gafner, PhD, for his contributions to this project.

 

By Hannah Bauman

 

Overview

A stand of wakame underwater

Wakame (Undaria pinnatifida, Alariceae) is an annual species of brown kelp that is native to the coastal waters of the northwestern Pacific Ocean, with a range that stretches from Hong Kong to northern Russia.1,2 Other common names for wakame include Asian kelp, precious sea grass, and sea mustard; chun dai cai and qun dai cai (Chinese); and miyeok or miyok (Korean). Though it is native to colder waters, it is highly adaptable and grows well in a variety of temperatures and on different surfaces. Due to this adaptability, it can be an invasive species outside its native habitat.

Wakame fronds consist of a holdfast (the “root” section that anchors onto the bedrock), a stipe (stem), and blade (leaf). These fronds can grow 1-3 meters long, and the blades are golden brown with many lobes attached to a midrib. The lower section of the fronds extend into pinnae, or wings.1 Wakame exhibits some physical differences based on whether it grows in northern or southern waters; “northern” wakame typically has a longer stipe and a more deeply divided blade than “southern” wakame.2

Wakame is a diploid sporophyte, which means that it reproduces by forming sporophylls (leaves that produce spores) at the base of the stipe in late spring and early summer.2 These sporophylls discharge zoospores, which germinate in close proximity of the parent plant and go into dormancy until the water temperature drops below 25°C (77°F) in the autumn. The zoospores produce either male or female gametophytes, and after these spores fertilize each other, small juvenile sporophytes mature into the adult form. In its microscopic (gametophyte) stage, wakame can migrate long distances by attaching to ocean life like oysters or man-made structures such as boat hulls.

Historical and Commercial Uses

Botanical illustration of wakame from 1870Wakame has been used traditionally along its native range to treat fever, difficulty urinating, lumps and swelling, and as a dietary supplement after childbirth.3 The use of wakame post-childbirth is common in the Korean peninsula, and miyeok-guk, or seaweed soup, was eaten postpartum to restore nutrients to the body. In Korean tradition, people often eat miyeok-guk on their birthdays to commemorate their mother.4

In China, wakame is one of the most widely consumed species of seaweed and has been used in traditional medicine for thousands of years. It is most often used to aid in conditions like edema (fluid retention in body tissue) and diuresis (excessive urination) and alleviate phlegm and swelling.5 It is also a common food item and is typically sold dried or salted.6 In Japan, wakame is a popular ingredient in miso soup and salads.

Seaweed-derived alginates, which are available in both free acid and salt forms, have a history of use in gastrointestinal disorders. Sodium alginate is an ingredient in over-the-counter acid reflux products such as Gaviscon® (GSK Plc; Brentwood, UK) and alginic acid isolated from wakame is authorized for use in several countries, including Belgium, Canada, Germany, Japan, and the United States, for the treatment of gastritis and gastroduodenal ulcers.7 Alginic acid from seaweed, including wakame, is Generally Recognized as Safe by the US Food and Drug Administration as a food additive for soup and soup mixes as an emulsifier, stabilizing agent, or thickener.9

Wakame is also a source of other active compounds including fucoidans, a group of polysaccharides that are found in the cell walls of brown kelp. Fucoidans are used as ingredients in dietary supplements and cosmetics, and fucoidan preparations have been proposed as a replacement for the conventional injectable anticoagulant heparin, which is often used to prevent and treat blood clots.

Seaweed, including wakame, also is used as a feed supplement for commercial livestock and fishery operations. Sea bream hatcheries that replaced 5% of the typical feed with wakame reported improved growth rate and nutrient absorption in their fish.7 Due to wakame’s prolific growth, it is a readily available and sustainable source of nutrients that can translate to a commercial scale.

Wakame accumulates minerals, heavy metals, and carbon from the ocean around it. Therefore, it can act as a biofilter for contaminated waters, and large kelp forests may play a role in mitigating the effects of climate change.7,10

Phytochemicals and Constituents

An herbarium entry for wakame from the Auckland MuseumWakame contains fiber, protein, and lipids in the form of fatty acids. Like many varieties of brown kelp, wakame also contains beneficial phytochemicals and elements including carotenoids, iodine, and magnesium. The National Institutes of Health’s recommended daily allowance for iodine is 150 mcg for adults, and wakame contains approximately 42 mcg per gram.10,11 This puts it among the richest plant source of iodine in the world. Iodine supplementation can reduce the risk of an enlarged thyroid gland (also known as a goiter), which can affect hormone production. The low incidence of common cancers, including breast and prostate cancers, in Japan is attributed in part to the widespread consumption of iodine from seaweed.11

Wakame contains approximately 35-46% fiber, the majority of which is soluble polysaccharides.7 Consuming this type of fiber can reduce postprandial glucose levels and digestive tract transit time. Polysaccharides in wakame include laminarin, alginic acid, and fucoidans. Alginates, which are available in both free acid and salt forms, can lead to a decrease in cholesterol levels and exert an antihypertensive effect. They are not known to be found in land plants. The cholesterol-lowering effects of alginates may be due to their ability to absorb cholesterol in the digestive system and eliminate it from the body. Due to its protective effect on skin and mucous membranes, sodium alginate has been used topically on wounds that have become infected.

Fucoidans are another group of polysaccharides that are found in the cell walls of brown kelp. It is speculated that fucoidans protect the seaweed from desiccation when exposed to the sun.7 Fucoidans stimulate the immune system, inhibit viral replication, and are known to exhibit anti-tumor activity, though the mechanism of action for this is not fully understood. In vitro trials have shown that fucoidans isolated from wakame exhibited stronger cytotoxic activity against some breast cancer and melanoma cell lines compared to fucoidan isolated from Saccharina japonica (Laminariaceae), another type of brown kelp.6 The fucoidan isolated from wakame is sulfated galactofucan, and the presence of sulfate affects the bioactivity of this fucoidan.

Wakame contains antioxidant carotenoids, the consumption of which can reduce oxidative stress in the body.6 Fucoxanthin, one of the most abundant carotenoids in nature, has been shown to have significant cytotoxic effects against prostate cancer cells in vitro and in mice.

The proteins found in wakame contain eight out of the nine essential amino acids. In addition to threonine, valine, leucine, lysine, methionine, histidine, phenylalanine, and tryptophan, wakame also contains glycine, alanine, cysteine, tyrosine, and high amounts of arginine.7 The amino acid score of wakame is 100, which is comparable to animal proteins, and the seaweed consists of approximately 24% protein by weight.

The main type of lipids found in wakame are polyunsaturated fatty acids. Marine phospholipids in wakame include palmitic acid, stearic acid, palmitoleic acid, oleic acid, linoleic acid, linolenic acid, and omega-3 fatty acids, which exert anti-inflammatory effects that have benefits for cardiovascular health.7

 

Table 1. Compounds Found in Wakame5-7

Compound Type

Compounds

Plant Part

Activities

Polysaccharides

Alginic acid, fucoidan, laminarin

Blade, stipe, sporophylls

Antibacterial, anticoagulant, anti-inflammatory, antiviral, cholesterol-lowering, cytotoxic, immunomodulating

Carotenoids

Beta-carotene, fucoxanthin

Blade, stipe

Antioxidant, antiproliferative, cytotoxic

Fatty acids

Palmitic acid, stearic acid, palmitoleic acid, oleic acid, linoleic acid, omega-3 fatty acids

Blade, stipe

Anti-inflammatory, antioxidant, immunomodulating

Sterols

Fucosterol, brassicasterol, beta-sitosterol

Blade, stipe

Cholesterol-lowering

 

Modern Research and Potential Health Benefits

Dried wakame in a Korean marketThe current research on wakame focuses on isolating specific compounds and investigating their bioactivity in vitro and in vivo. Extracts of alginates, fucoidans, and laminarin were effective against E. coli and Staphylococcus bacteria in vitro, and sodium alginate showed the strongest ability to bind to and kill these bacteria.7 Sulfated fucoidan also showed antimalarial activity in vitro, inhibiting host cell invasion by Plasmodium falciparum parasites.12 Fucoidan also showed inhibitory activity against human immunodeficiency virus (HIV) and the virus that causes herpes. Wakame-derived fucoxanthin demonstrated in vitro cytotoxic effects against leukemia cells and induced apoptosis (normal, pre-programed cell death).6

Due to its anticoagulant properties, fucoidan preparations have been tested as an alternative to the blood-thinning medication heparin, which is sourced from animal mucosa. Plant-based sources of fucoidan are less susceptible to contamination with prions or viruses than animal sources. Purified fucoidan is less potent than heparin in timed assays, but it activates a different pathway than heparin and has shown significant antithrombotic effects.12 Fucoidan’s antioxidant activities may have potential uses in chronic inflammatory disorders like arthritis and Alzheimer’s disease.7

Sodium alginate from wakame inhibits acid reflux due to its ability to form a barrier on contact with gastric acid, converting into a more neutral pH foam that floats on the stomach contents and further prevents reflux.13 The anti-ulcer activity of sodium alginate is due to its anti-inflammatory and antibacterial activities, as it is active against Helicobacter pylori bacteria in the gut and can aid in the regeneration of the mucous membrane in the stomach.7 The impact of sodium alginate and alginic acid derivatives on gut health can also aid in other conditions. A small, open-label clinical trial on men with type 2 diabetes mellitus associated sodium alginate supplementation, when taken with food, with significantly slower gastric emptying and lower blood sugar and insulin levels after eating.14 In a separate trial, overweight participants who ate a calorie-restricted diet supplemented with alginic acid lost significantly more weight by the end of the trial than the participants on a restricted diet alone.7

Pilot trials have been conducted on wakame as a whole food, further investigating its effects on blood sugar and insulin levels. These trials have correlated the consumption of wakame with lower blood sugar levels and insulin resistance compared to control meals that did not include wakame.15,16 In one trial, seaweed consumption also was associated with increased satiety.15

Laminarin has shown immune-enhancing effects in vitro, such as increasing the number of red blood cells and “helper” T cells. It is also used as an ingredient in surgical dusting powders, which are used on major wounds or burns as an antiseptic and astringent agent to keep the area clean and aid healing.7

Consumer Considerations

Wakame is cultivated on a commercial scale throughout the Pacific Ocean and there are currently no sustainability concerns.

Consuming excess iodine can cause negative side effects, particularly in those with pre-existing thyroid conditions.11 Hyperthyroidism can result from the over-consumption of iodine, and the symptoms of this condition can include nervousness, inability to sleep, rapid heartbeat, weight loss, sweating, and more frequent bowel movements. However, some foods, particularly in the Brassicaceae family, contain goitrogens that can limit iodine uptake by the thyroid. Consuming wakame and these foods together can prevent excess iodine from affecting the thyroid. Because wakame accumulates heavy metals and other environmental contaminants, those who choose to forage for wakame should be cautious in choosing a site.

Nutrient Profile
Per 100 g of wakame17

Macronutrients:

45 calories
3 g protein
9.1 g carbohydrate
0.6 g fat
0.5 g dietary fiber

Micronutrients:

Excellent source of:

Manganese: 1.4 mg (60.9% DV)
Folate (Vitamin B9): 196 mcg (49% DV)
Magnesium: 107 mg (25.5% DV)

Very good source of:

Riboflavin (Vitamin B2): 0.23 mg (17.7% DV)
Pantothenic acid (Vitamin B5): 0.7 mg (14% DV)
Iron: 2.18 mg (12.1% DV)
Calcium: 150 mg (11.5% DV)

Good source of:

Niacin (Vitamin B3): 1.6 mg (10% DV)
Vitamin E: 1 mg (6.7% DV)
Phosphorus: 80 mg (6.4% DV)
Thiamin (Vitamin B1): 0.06 mg (5% DV)

Also provides:

Zinc: 0.38 mg (3.5% DV)
Vitamin C: 3 mg (3.3% DV)
Vitamin A: 18 mcg (2% DV)
Potassium: 50 mg (1.1% DV)

Trace amounts:

Vitamin B6: 0.002 mg (0.1% DV)

DV = Daily Value as established by the US Food and Drug Administration, based on a 2,000-calorie diet.

 

Recipe: Miso Soup
Adapted from Masaharu Morimoto18

Ingredients:

  • 4 cups dashi (dried fish and kelp stock), instant or homemade
  • 1/4 cup shiro (white) miso, plus more if necessary
  • 1/2 cup drained silken tofu
  • 1 generous tablespoon thinly sliced scallion (preferably light green parts)
  • 2 tablespoons dried wakame seaweed, soaked in cold water for five minutes, then drained well

Directions:

  1. Bring the dashi to a very gentle simmer in a small pot. Put the miso in a small bowl, spoon in about 1/2 cup of the hot dashi, and stir, breaking up clumps, until very smooth. Pour the mixture back in the pot.
  2. Use a spoon to scoop small chunks of the tofu into the pot. Add the scallion and seaweed, stir very gently, and wait just until the tofu is heated through, about one minute. Season with more miso to taste, mixing it with a little hot soup before adding it. Ladle the soup into bowls and eat right away.

 

Image credits (top to bottom):

An underwater stand of wakame. Image courtesy of CSIRO.
Wakame illustration from Algae Japonicae by Willem Frederik Reinier Suringar. 1870.
Wakame specimen in the Auckland Museum Herbarium.
Dried wakame in a Korean market. Image courtesy of manray3.

 

References

  1. Ohno M, Mizuta H. Undaria pinnatifida (Asian kelp). CABI Invasive Species Compendium website. October 13, 2011. Available at: www.cabi.org/isc/datasheet/59979. Accessed August 1, 2022.
  2. Undaria pinnatifida. Smithsonian Environmental Research Center website. Available at: https://invasions.si.edu/nemesis/species_summary/-21. Accessed August 1, 2022.
  3. Khan MNA, Yoon SJ, Choi JS, et al. Anti-edema effects of brown seaweed (Undaria pinnatifida) extract on phorbol 12-myristate 13-acetate-induced mouse ear inflammation. Am J Chin Med. 2009;37(2):373-381.
  4. Cho E. Korean Culinary Cures: From Tummy Aches to Hangovers, Here's How Moms Cook Up Relief. NPR. May 9, 2018. Available at: www.npr.org/sections/thesalt/2018/05/09/609440146/korean-culinary-cures-from-tummy-aches-to-hangovers-heres-how-moms-cook-up-relie. Accessed August 1, 2022.
  5. Zeng J, Luan F, Hu J, et al. Recent research advances in polysaccharides from Undaria pinnatifida: Isolation, structures, bioactivities, and applications. International Journal of Biological Macromolecules. 2022;206:325-354.
  6. Zhao Y, Zheng Y, Wang J, et al. Fucoidan extracted from Undaria pinnatifida: Source for nutraceuticals/functional foods. Mar Drugs. 2018;16(9):321. doi: 10.3390/md16090321.
  7. Holdt S, Kraan S. Bioactive compounds in seaweed: Functional food applications and legislation. Journal of Applied Phycology. 2011;23(3):543-597. doi:10.1007/s10811-010-9632-5.
  8. Department of Health and Human Services. 21CFR § 184.1011 Alginic acid. Code of Federal Regulations. Silver Spring, MD: US Food and Drug Administration; 2022.
  9. Duarte CM, Gattuso JP, Hancke K, et al. Global estimates of the extent and production of macroalgal forests. Global Ecology and Biogeography. 2022;31(7):1422-1439.
  10. Daily Values. National Institutes of Health website. Available at: https://ods.od.nih.gov/HealthInformation/dailyvalues.aspx/. Accessed September 13, 2022.
  11. Zava TT, Zava DT. Assessment of Japanese iodine intake based on seaweed consumption in Japan: A literature-based analysis. Thyroid Res. 2011;4:14.
  12. Berteau O, Mulloy B. Sulfated fucans, fresh perspectives: Structures, functions, and biological properties of sulfated fucans and an overview of enzymes active toward this class of polysaccharide. Glycobiology. 2003;13(6):29R-40R.
  13. Mandel KG, Daggy BP, Brodie DA, Jacoby HI. Review article: Alginate-raft formulations in the treatment of heartburn and acid reflux. Aliment Pharmacol Ther. 2000 Jun;14(6):669-690.
  14. Torsdottir I, Alpsten M, Holm G, Sandberg AS, Tölli J. A small dose of soluble alginate-fiber affects postprandial glycemia and gastric emptying in humans with diabetes. Journal of Nutrition. 1999;121(6):795-799.
  15. Zaharudin N, Tullin M, Pekmez CT, Sloth JJ, Rasmussen RR, Dragsted LO. Effects of brown seaweeds on postprandial glucose, insulin and appetite in humans – A randomized, 3-way, blinded, cross-over meal study. Clinical Nutrition. 2021;40(3):830-838.
  16. Yoshinaga K, Mitamura R. Effects of Undaria pinnatifida (wakame) on postprandial glycemia and Insulin levels in humans: A randomized crossover trial. Plant Foods for Human Nutrition. 2019;74:461-467.
  17. Seaweed, wakame, raw. FoodData Central website. US Department of Agriculture Agricultural Research Service. Available at: https://fdc.nal.usda.gov/fdc-app.html#/food-details/170496/nutrients. Accessed September 12, 2022.
  18. Morimoto M. Mastering the Art of Japanese Home Cooking. New York, NY: Ecco; 2016.
References