The fact that seaweeds are good for health is not news: the Japanese have long attributed healing properties to them and have used seaweed (mainly kelp) extracts to treat a variety of ailments including goitre, tumours and worms.

The Romans are thought to have used seaweed to treat wounds, burns and rashes and the Irish have for centuries been making a seaweed tea from Irish moss as a remedy against the common cold and hangovers. The Inuit get an important portion of their vitamin C from brown seaweeds.

It is only recently, though, that the mechanisms behind these properties have been researched, backing up traditional knowledge with scientific reasoning and explaining how exactly seaweed benefits us. For instance, it has been proven that dulse, the seaweed traditionally used as a cure for worms, contains kainic acid, which does indeed kill intestinal parasites.

Moreover, recent UK research indicates that compounds in seaweed inhibit the absorption of fat and carbohydrates in our bodies, meaning it can thus start to play an important role in combating obesity and aiding weight loss, of course as part of a healthy diet.

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Vitamins and minerals

Seaweeds contain a large number of vitamins but it is the red and green types that have the widest range.

Of particular interest is vitamin B12 which is mostly found in its naturally occurring state in meat. Natural vegetarian options that contain it include milk, yogurt, cheese and eggs, but for vegans seaweed is pretty much the only source.

Seaweeds are rich in calcium, iodine, copper, iron, magnesium, potassium and zinc. Often they contain them in quantities greatly exceeding those of land plants. For example, dulse, sea lettuce and gutweed contain over 25 per cent more iron than meat, arame and wakame contain ten times more calcium than milk and dulse contains more vitamin C than oranges. However we generally consume smaller quantities of seaweed in the context of a recipe.

Seaweed is not only rich in vitamins and minerals, but it also contains compounds with anti-oxidative properties, protein and fibre.

Seaweeds and heavy metals

The reason why seaweeds are such a good source of minerals is that they are very effectively able to ‘absorb’ them from seawater and concentrate them.

The downside is that, along with the beneficial minerals, they also act like a sponge and take in a number of heavy metals that pollute waterways – indeed, some marine ecologists use seaweeds as a way to monitor levels of pollutants in the water.

Of these heavy metals, arsenic is the most problematic and poses the greatest toxicity risk. It has been found in most seaweed species, but of particular concern is hijiki, and many countries, including England, Canada and New Zealand, now recommend that you do not eat it, unless is comes from a verifiable certified organic source.

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This nutritional information is taken from The Seaweed Cookbook by Caroline Warwick-Evans and Tim Van Berkel, publisher Lorenz Books, RRP £15.