Which item is the misfit in this group: a man, a milk thistle, or a mushroom?
Okay, it’s a trick question. In terms of scientific classification, mushrooms are as different from flowering plants as humans are. In fact, fungi aren’t even part of the Plant Kingdom—they have a kingdom all their own.
Fungi are primitive compared with flowering plants, which make up the overwhelming majority of the world’s culinary and medicinal herbs. Flowering plants use photosynthesis to convert sunlight and carbon dioxide into their primary food, a sugar called glucose. Glucose is also the primary food for animals, including humans, and comes from our food. When we talk about blood sugar, we mean glucose.
In comparison, fungi “steal” glucose from plants and animals. Fungi are either saprophytes, which obtain nutrients by digesting dead organisms, or parasites, which feed off the living. Mushrooms growing on a dead log come to mind—these fungi are taking advantage of years of work done by the tree to store energy in its trunk.
Fungi aren’t primitive when it comes to manufacturing phytochemicals, however, which makes the distinction between fungi and true plants nearly invisible to the chef or herbalist. Some fungi produce phytochemicals that create delicious aromas and tastes, making mushrooms such as morels, truffles, and corn smut prized culinary ingredients. Other mushrooms have ghastly stenches or are hallucinogenic or poisonous. In between lies a group of medicinal mushrooms that may or may not be tasty, but possibly provide health benefits. Of 10,000 species of mushrooms, about 700 are considered edible and less than 200 are considered medicinal.
The mushrooms shiitake (Lentinula edodes), reishi (Ganoderma lucidum), maitake (Grifola frondosa), and hoelen (Poria cocos) are used in traditional Asian medicine to stimulate the immune system and treat chronic wasting diseases such as cancer, tuberculosis, hepatitis, and AIDS.
Common to all these mushrooms are phytochemicals called glycans, proteoglycans, beta-glucans, and polysaccharides. In a nutshell, these compounds are forms of glucose, that all-important energy source. In nature, glucose molecules link together to form polymers, chemical compounds built like chains or netting of repeating structural units such as sugars. The term polysaccharide means just that—many sugars.
Glucose molecules linked together in one way create digestible starches such as potatoes or rice. Glucose linked together in a different way is not digestible, but makes for healthy dietary fiber. The glucose most important to mushrooms comes in long chains and forms the cellulose in a tree trunk.
Mammals can’t digest cellulose, so we can’t obtain glucose from wood. But mushrooms can, and some mushrooms use cellulose to make unique, highly branched polymers. The branching in these polymers, called beta-glucans, differs from other glucoses—and this distinct structure may be what makes mushrooms medicinal.
Beta-glucans extracts of shiitake, reishi, maitake, hoelen, and other fungi have repeatedly been shown to slow, reverse, or prevent the growth of tumors in animals and humans in clinical trials. A 1987 Japanese study noted that the antitumor activity of beta-glucans increased as the degree of branching increased, with shiitake and maitake among the most branched, thus most effective.
Mushroom extracts prevent tumor growth not by killing cancer cells, but by increasing immune cell activity. In a 1992 University of Hawaii study, mice with lung cancer survived longer if they received reishi extract along with chemotherapy than those untreated or given chemotherapy alone. However, when the mice were given a drug that suppressed immune cells, the drug counteracted the mushroom extract. Mushrooms may increase immunity because of their primitive nature. When mushroom beta-glucans are linked to proteins, they mimic many bacterial cell walls; this may fool the body’s immune cells into gearing up for a fight because they think bacteria have invaded.
So while many fungi are closer relatives to bacteria than they are to flowers or us, that distance may be part of how they help us heal. In the meantime, a legacy of traditional use shows they’re powerful medicine.
• Chang, R. “Functional properties of edible mushrooms.” Nutrition Reviews 1996, 54:S91–S93.
• Furusawa, E., et al. “Antitumor activity of Ganoderma lucidum, an edible mushroom, on intraperitoneally implanted Lewis lung carcinoma in synergenic mice.” Phytotherapy Research 1992, 6:300–304.
• Nanba, H., A. Hamaguchi, and H. Kuroda. “The chemical structure of an antitumor polysaccharide in fruit bodies of Grifola frondosa (Maitake).” Chemical and Pharmacological Bulletin (Japan) 1987, 35:1162–1168.
James Duke is an Herbs for Health Editorial Advisory Board member and author of The Green Pharmacy (Rodale, 1997).
C. Leigh Broadhurst holds a doctorate in geochemistry and is a nutrition consultant in Clovery, Maryland.