Seaweed: the most nutritious form of vegetation on the planet?

Without a doubt, seaweed is the hottest functional ingredient in town. Not only is it packed with almost all of the important nutritional components, it contains them in levels that often far exceed its terrestrial counterparts: vegetables. It is now known that seaweed contains numerous bioactive substances shown to lower cholesterol, reduce blood pressure, promote healthy digestion and tackle free radicals. Add to this the fact that it is virtually fat and calorie free and it is easy to see why seaweed is building a reputation as the new 'superfood'.

So, what seaweeds are edible?

In theory, most seaweeds are edible but whether they are palatable is a different matter. As many as 500 species of seaweed are harvested or cultured and every year millions of tonnes are used to supply the food industry. Asian countries - in particular China, Japan and Korea - are the primary users of seaweed for food. In 2002 a staggering 8Mt was used to supply China alone. Asian cuisine is rich in dishes that use fresh and dried seaweed directly as 'sea vegetables' or as flavourings in soups, stews and sauces. More than 20 species are commonly used but kombu (Laminaria spp) and nori (Porphyra spp) are the most popular. Nori is sold in dried sheets and is used to wrap dishes like sushi; the Japanese consume 9,000M sheets of nori per year.

In Europe, traditional uses of seaweed are not as common as in Asia but some species such as laver (Porphyra spp) and dulse (Palmaria palmata) are found in the coastal towns of Ireland and the UK.

A great source of fibre

If you type a few key words into Google then you will soon discover numerous websites extolling the health and well-being attributes of seaweeds or sea vegetables. But is any of this information backed by scientific investigation? Well, yes, there is strong evidence to suggest that seaweeds have the potential to be nutritionally beneficial components of foodstuffs either as wholefoods or as extracts. Typically, the modern diet is high in refined and processed products and lacks the necessary levels of dietary fibre, minerals and vitamins that are necessary to keep our bodies healthy. Many of the illnesses and diseases that plague western society appear to be diet-related, and there is growing evidence that the incorporation of seaweed into a balanced diet could help.

Gut health

Dietary fibre is needed to clear the digestive tract, protect surface membranes in the stomach and intestine against ulcers and carcinogens and to eliminate unwanted cholesterol and salt. Weight for weight comparisons show seaweeds to contain levels of fibre that are comparable to or greater than vegetables. A 100g portion of Laminaria digitata contains 6.2% fibre, higher than that in equivalent portions of prunes, apples, bananas and brown rice.

Much of the algal fibre is water soluble and some fibres are not digested in the small intestine at all. This aids in decreasing lower bowel transit time, improves faecal bulking and water retention, and promotes bacterial population of the lower bowel. As the fibre in seaweed is non-starch based it also lowers the overall ratio of fibre to carbohydrate, indicating that seaweeds probably have a lower glycaemic index (GI) than vegetables.

Heart Health

Several studies on the effects of seaweeds or seaweed extracts on blood cholesterol levels have found that there is an overall decrease in cholesterol.

Studies using alginates have found that cholesterol absorption in the gut is reduced and this then reduces plasma cholesterol levels most likely due to the entrapment and bulking effects of the alginates. Brown seaweeds in particular contain high levels of sterols. Fucosterol has also been shown to restrict the solubility of cholesterol in bile and therefore lower the absorption of cholesterol in the bloodstream.

High blood pressure can result from an imbalance in sodium and potassium, and deficiency in other minerals such as magnesium and calcium can also lead to vasoconstriction. Seaweeds typically contain high levels of potassium, magnesium and calcium and have been shown to have a positive effect on regulating mineral balances and blood pressure.

The omega-3 to omega-6 ratio in seaweeds is also closely matched, a factor that has been shown to be important in a balanced diet.

Antioxidants

Seaweeds contain large amounts of antioxidants and polyphenols (known as phlorotannins). Phenols and polyphenols are present in many fruits and vegetables and constitute an important anti-cancer active group in nutrition. Their role in seaweed survival is linked to the exposure levels that seaweeds experience on contact with UV light. Seaweeds are exposed to many of the same conditions which cause free radical formation as humans, but appear to be relatively free from the effects of these agents. This indicates that seaweeds contain protective antioxidative defence systems and many studies have demonstrated in vitro antioxidant activity in a range of them.

A number of seaweed derived polysaccharides, minerals and vitamins have also been shown to have antioxidant properties. Vitamin B12 is usually found in animal foodstuffs but seaweeds provide one of very few plant sources of this vitamin. A 100g portion of Ulva lactuca can provide up to 35% of the recommended daily intake. Seaweeds are also a good source of selenium.

Immune system enhancement

As with other seaweed polysaccharides, there is evidence of anticoagulant activity in fucoidan fractions.There is also some evidence that fucoidans can enhance vascular tube formation, further enhancing interest in the cardiovascular area. Fucoidans can also inhibit the inflammatory changes induced by pneumococcal meningitis and could replace pharmaceutical anti-inflammatories.

Bone health

Seaweeds contain a high level of calcium, which is normally associated with the polysaccharides, such as alginates or carrageenans. Calcium is also bound and can comprise up to 7% of the dry weight. For some calcareous seaweeds such as Lithothamnion calcareum the calcium content can be up to 35%. This form of calcium has been found to be more bioavailable that calcium carbonate for use in supplements.

Widening seaweed consumption will be a challenge. Its health benefits are not in doubt, but consumers are generally not prepared to compromise on taste and aroma. Seaweed flavours are certainly unique but isn't it time that we faced a new culinary challenge?

Some of our best known chefs are already tempting customers with dishes like crystallised seaweed in oyster vinaigrette, beef stew made with seaweed stock and salmon with pickled seaweed. So why not give it a whirl?

Dr Sarah Hotchkiss and Dr Angie Trius are from Cybercolloids, an organisation devoted to bringing innovation to the hydrocolloids industry. Contact: http://www.cybercolloids.net​

Tel: +353 21 4370903