The health benefits of consuming seaweed were recognised over three thousand years ago, particularly in Asia, where marine algae are still prized for their nutritional content. The vast majority of marine algae are edible, with only a few tropical species being poisonous. Some species, however, are specially selected for their appealing flavour, texture or culinary versatility; these include dulse (Palmaria palmata), nori (Porphyra tenera), sea lettuce (Ulva lactuca) kombu (Laminaria japonica), wakame (Undaria pinnatifida), arame (Eisenia bicyclis), hijiki (Hizikia fusiforme) and agar-agar (Sphaerococcus euchema).
Sea vegetables are low in fat, low in calories and rich in essential minerals, vitamins and protein. The mineral content of seaweeds is very significant and is likely to explain many of their beneficial effects on health. Seaweeds provide all of the 56 minerals and trace minerals required for the body’s physiological functions. Indeed, they contain 10 to 20 times the minerals of land plants and an abundance of vitamins and other elements necessary for metabolism. The modern diet is severely depleted of minerals due to a general decline in soil and crop mineral content, and to refining and processing which strips food of minerals and other vital nutrients. Thus, addition of seaweed into the diet is very important to ensure adequate intake of minerals, which are in a highly assimilable form because they are integrated into living plant tissue. Sea vegetables are especially useful for vegetarians and those abstaining from dairy foods because of their high levels of calcium, iron and iodine.
In addition to minerals, seaweeds contain vitamins A, B, C, and E, and Porphyra species are reported to contain vitamin D. Moreover, some seaweeds contain what appears to be vitamin B12, which is normally found only in animal products.
Seaweeds contain 50 to 60% polysaccharides, notably cell wall structural polysaccharides that are extracted by the hydrocolloid industry. Despite this large quantity of carbohydrate, sea vegetables add few calories to the diet; this is because much of their starch consists of a substance called algin. Alginates are not easily digested by the body, acting like soft fibre, soothing and adding bulk to the digestive tract. Scientific studies have shown that alginates inhibit absorption of toxic metals and radioactive isotopes such as strontium-90 in the digestive tract. All sea vegetables contain significant amounts of protein, sometimes as much as 48%.
Lipids represent only 1-5 % of algal dry matter and show an interesting polyunsaturated fatty acid composition, particularly regarding omega 3 and omega 6 acids which are concentrated in the galactolipid fractions.
Sea vegetables have traditionally been used in Asia to treat cancer, heart disease and thyroid problems. Other medicinal uses are currently being investigated. Scientific research aimed at
explaining the positive effects of seaweeds on health is in progress. Some key findings related to breast cancer, heart disease, thyroid problems, immune function, inflammation, and anti-bacterial and anti-viral activity are reviewed in a peer-reviewed paper by Jane Philpott MA (Oxon), MSc, PhD in the Nutrition Practitioner Journal. The paper also includes practical information on how to prepare and cook nori, arame, dulse, kombu, wakame, hijiki and agar-agar is given, as well as some recipes.
For information and practical tuition in cooking and eating sea vegetables, come to a Cooking for Health course, held throughout the year in Somerset, UK.