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MUSHROOM NUTRITION

Alongside plants and animals, fungi form one of the three main kingdoms of living organisms. Unlike plants, which derive carbon from carbon dioxide in the air, fungi, together with animals, derive carbon from the breakdown of organic matter and, together with bacteria, they are the major decomposers in most ecosystems, playing an important role in the recycling of nutrients.

Fungi themselves are divided into a number of different classes or phyla:

• Chytridiomycota
  
• Blastocladiomycota
  
• Neocallimastigomycota
  
• Glomeromycota
  
• Zygomycota
  
• Ascomycota
  
• Basidiomycota
  

Most of the fungi in these classes are relatively simple, often unicellular structures and include such groups as yeasts and moulds. Many of these organisms produce medically useful substances, for instance beta-glucans from yeasts and antibiotics from moulds such as penicillin, but only the so called 'higher fungi', those that produce an above ground fruiting body, can properly be called mushrooms.

To date around 14,000 species of mushroom have been described, although it is estimated that there are actually ten times this number. They are divided into Ascomycetes and Basidiomycetes according to how they produce spores. In Ascomycetes they are produced within microscopic cells called asci while in Basidiomycetes the spores develop on projections that grow out from microscopic cells called basidia.

The majority of the mushrooms produced commercially fall within the Basidiomycota. These include gill fungi where the basidia line delicate gills on their undersurface (eg. the common button mushroom, Shiitake and Oyster mushrooms), Jelly fungi where the basidia are buried in the body of the fungus and only the spores protrude beyond the surface (eg.Auricularia sp.) and Polypores where the basidia line thin tubes opening into pores on their undersurface (eg. Reishi and Maitake). A relatively few medicinal mushrooms belong to the Ascomycota (eg. Cordyceps sp.).

Although the above ground fruiting body or mushroom forms the most visible part of these organisms, the largest part of any mushroom exists below the surface in the form of fine filaments or hyphae which penetrate the substrate on which the mushroom is growing, secreting enzymes to digest it and absorbing the nutrients released. These filaments form a dense network or mycellium.

Cultures as diverse as the Indians of the Americas, Siberian shamans and the pre-historical peoples of North Africa have all prized mushrooms for their psychoactive properties. However, from and early date mushrooms have also been appreciated for their nutritional and medicinal properties.

When the well preserved body of a neolithic man who had died around 3300 BC was found in the Italian alps in 1991 he was carrying two polypores. One of these has noted antibacterial properties while the other has traditionally been used as tinder for help in lighting fires as well as to treat gastrointestinal conditions.

Dioscorides included mushrooms in his great work De Materia Medica (55AD), which remained the standard text in the West until around 1600 AD and they are also mentioned by Gerrard in his influential Herbal (1663).

Other cultures around the world have used mushrooms for their varied health benefits but nowhere have their medicinal properties been explored as thoroughly as in China. The earliest extant Chinese materia medica, the Shen Nong Ben Cao, dating to around 250 AD, contains 365 herbs, including four mushrooms all of which are classified in the 'Superior' category of herbs which are considered safe to take for long periods of time without side effects and with broad adaptogenic benefits:

• Ling Zhi (Ganoderma lucidum)
  
• Fu Ling (Poria cocos)
  
• Bai Me Er (Tremella fuciformis)
  
• Zhu Ling (Polyporous umbellatus)
  

In his authoratative materia medica, the Ben Cao Gang Mu (1578), Li Shi Zhen included 21 mushrooms and their place as a symbol of immortatlity in oriental culture is attested to by their extensive depictation in painting, carving and embroidery.

Drawing on this extensive traditional knowledge, researchers in Japan began investigating the use of mushrooms in the treatment of cancer in the 1960's. Initially they focussed on the common culinary mushroom Shiitake (Lentinula edodes) and from it developed two commercial extracts, Lentinan and LEM with good anti-tumor efficacy.

Subsequently other researchers chose Coriolus versicolor on the basis of extensive screening and developed an extract PSK (Polysaccharide K) or 'Krestin' which went on to acheive huge commercial success with sales by 1987 of US$600 million a year. This was followed by researchers in Hong Kong developing another extract from Coriolus versicolor, PSP (Polysaccharide Peptide) with similarly impressive immune modulating and anti-tumour properties.

The commercial success of these products led to a massive increase in interest in the clinical possibilities of mushroom nutrition with different groups of researchers focussing on different mushrooms to the point where there are now dozens of mushroom products competing for attention - see Understanding Mushroom Products.