Seaweed has long been part of the traditional diet of coastal communities. It is still widely consumed in East Asia, particularly Japan, China and Korea, but not to any great extent in Europe. Seaweed has been attracting interest recently as a valuable food source with a number of health benefits - time for some facts.
Types of seaweed
Seaweed is a type of algae that grows in salt water and (like terrestrial plants) needs sunlight to thrive. There are over ten thousand varieties of seaweed, many of which are good to eat. Nori is a commonly consumed red seaweed. In Japan, nori is used to wrap sushi, but it is also known as sloke in Scotland and laver in Wales where it was traditionally made into flat breads. Kombu and wakame are types of brown seaweed and are widely used in the Far-East as flavouring agents in stews and soups. Green seaweeds like sea lettuce and sea grass, which flourish around the shores of Great Britain, Ireland and Scandinavia, can be eaten raw in salads or cooked in soups. Other seaweeds used as foods include hijiki, wrack, sea spaghetti, dulse and Irish moss or carrigeen. Seaweed is usually sold commercially in the dried form.
A recent study analysed the nutrient levels of a variety of edible seaweeds and compared a typical portion (8 g dried) with recommended daily intakes, and with common foods.1
As seaweed absorbs minerals from the sea, it is rich in many minerals and trace elements. Calcium and iron tend to accumulate at much higher levels in seaweed than in terrestrial plants. For example, an 8 g portion of dried kombu provides much more calcium than a cup of milk, and a portion of dulse contains more iron than a 100 g sirloin steak (although it may not be as well absorbed). Seaweed also provides large quantities of iodine vital for thyroid function. However, the German Federal Institute for Risk Assessment has warned of seaweed varieties excessively high in iodine and recommends establishing safe upper iodine limits for seaweed products across the EU.2 Additionally, brown seaweed can accumulate heavy metals like arsenic. A study in 2004 found that hijiki seaweed contained significant amounts of arsenic.3 As a result, the UK Food Standards Agency now advises consumers to avoid eating hijiki.4 Finally, the often high sodium content of seaweed needs to be considered by those who have to care about their salt intake.
Seaweeds are rich in soluble fibres such as alginates, carrageenan and agar, which are not digested in the gut to any great extent and so can help increase feelings of satiety. Seaweed alginates and carrageenans are also employed to give processed foods (e.g., sausages, croissants) favourable texture and stability. Although seaweed fibre extracts may have some potential as slimming aids, seaweed itself is likely to have an effect on satiety (and weight control) similar to ordinary fruits and vegetables. An 8 g portion of dried seaweed provides about an eighth of an adult’s daily fibre needs, similar to the amount in a banana.1
Seaweed contains very small amounts of fat, and some varieties are rich in protein. Many contain levels of essential amino acids similar to pulses and eggs. Vitamins A, C and E are found in seaweed in useful amounts, and it is also one of the few vegetable sources of vitamin B12, making it a useful adjunct to a vegetarian or vegan diet.
Potential health benefits
Seaweed is used extensively in Chinese medicine but is largely unexplored as a therapeutic agent in the West. Preliminary research suggests that certain polysaccharides called fucoidans, typically found in brown seaweeds such as kombu and wakame, may exert anti-cancer activity.5 However, these potential health benefits have not yet been tested in humans. Seaweed fibres have beneficial effects on the digestive system and lipid metabolism. They also appear to have anti-inflammatory and antioxidant activity, but again, this remains to be shown in humans.6
Seaweed is an excellent source of fibre, minerals and phytonutrients.1 It is safe to eat, although care should be taken with some varieties as concerns potential levels of sodium, iodine or heavy metals. In general, seaweed can add usefully to a varied diet. Try it crumbled over rice, baked potatoes and salads, or added to soups, stock, beans and stews.
- MacArtain P, Gill CIR, Brooks M, Campbell R, Rowland IR. (2007) Nutritional value of edible seaweeds. Nutrition Reviews 65:535-543
- Gesundheitliche Risiken durch zu hohen Jodgehalt in getrockneten Algen. Aktualisierte Stellungnahme Nr. 026/2007 des Bundesamts für Risikobewertung vom 22. Juni 2004
- Rose M, Lewis J, Langford N, Baxter M, Origgi S, Barber M, MacBain H, Thoma K. (2007) Arsenic in seaweed-forms, concentration and dietary exposure. Food Chemistry and Toxicology 45:1263-1267
- Cumashi A, Ushakova NA, Preobrazhenskaya ME, D’Incecco A, Piccoli A, Totani L, Tinari N, Morozevich GE, Berman AE, Bilan MI, Usov AI, Ustyuzhanina NE, Grachev AA, Sanderson CJ, Kelly M, Rabinovich GA, Iacobelli S, Nifantiev NE. (2007) A comparative study of the anti-inflammatory, anticoagulant, antiangiogenic, and antiadhesive activities of nine different fucoidans from brown seaweeds. Glycobiology 17:541-542
- Shin HC, Hwang HJ, Kang KJ, Lee BH. (2006) An antioxidative and anti-inflammatory agent for potential treatment of osteoarthritis from Ecklonia cava. Archives of Pharmaceutical Research 29(2):165-171