A symbol of longevity in Asia because of their health-promoting properties, shiitake mushrooms have been used medicinally for more than 6,000 years. They are now cultivated worldwide for both culinary and medicinal purposes. They are champions in immune, anti-cancer and cardiovascular benefits. During the Ming Dynasty (A.D. 1368-1644) Chinese physician Wu Jue wrote that the mushroom could be used medicinally as a remedy for upper respiratory tract infections, poor circulation, liver pathologies, exhaustion, premature aging, and as a Qi (life force) tonic.
Like other mushrooms, these specialty mushrooms are as mysteriously unique as they are delicious. While often thought of as a vegetable and prepared like one, mushrooms are actually a fungus, a special type of living organism that has no roots, leaves, flowers or seeds.
Shiitake has a nutty and earthy taste, making it a common delicacy of the culinary world. Many chefs prefer to use sun-dried Shiitake since the drying process seems to enhance the flavour. Interestingly, the effect of UV light on the mushroom converts ergosterol into vitamin D, making the sun-dried variety a dietary source of this vitamin.
Most people are aware that the human body makes vitamin D in response to sunlight. Less known is the fact that mushrooms, even picked ones, can perform the same feat - which means that eating mushrooms that have been exposed to sunlight can be an excellent way to supplement your "D" levels.
In the summer of 2004, mycologist Paul Stamets discovered that the level of vitamin D in freshly picked, indoor- grown shiitake mushrooms rose from 110 IU (international units) to an astonishing 46,000 IU per 100 grams when the mushrooms were placed outdoors in the sun for just six hours with the gills facing up (when the gills were facing down, the level rose to 10,900 IU).
This means that eating just one gram of sun-treated shiitake - about one tenth of one mushroom - would give you 460 IU, close to the FDA's recommended daily dose of 400 IU. In his book, Mycelium Running: How Mushrooms Can Help Save the World, Stamets concluded, "(In) populations where vitamin D is seriously deficient, sun-exposed dried mushrooms can help address a serious health issue."
Immune System Benefits
From a naturopathic perspective, Shiitake is a fascinating mushroom due to its application in health care, easy incorporation into the diet, and excellent safety profile. Current research is discovering that extracts of this mushroom have immune system regulating properties, along with antibacterial, antiviral, and blood clot inhibiting properties. A study published by the Journal of Microbiology and Biotechnology in 2009 reported that polysaccharide extracts of Shiitake were shown to stimulate the function and activation of macrophages. Macrophages are white blood cells involved in the body’s initial response to infection (destroying pathogens and sending out chemical signals to the immune system to mount an attack on invading organisms).
No health benefit is better documented for shiitake mushroom than immune support. In fact, the immune support track record for this mushroom is fascinating. On the one hand, numerous studies have shown the ability of whole shiitake mushrooms to help prevent excessive immune system activity. On the other hand, an equal number of studies have shown the ability of shiitake mushrooms to help stimulate immune system responses under certain circumstances. In other words, from a dietary perspective, shiitake mushrooms appear able to enhance immune function in both directions, giving it a boost when needed, and cutting back on its activity when needed.
In 2006, the Biological Pharmacology Bulletin published a study that examined the efficacy of a hot water extract of Shiitake on protecting hepatocytes (liver cells) from the toxic agent D-galactosamine. The result was that 0.5 mg/ml of the Shiitake extract completely suppressed the cytotoxic (liver cell death inducing) effects of D-galactosamine. The study continued to examine the effect of injecting the Shiitake extract into rats treated with D-galactosamine. The result was less leakage of AST and ALT (both chemical blood markers of liver cell injury).
The most famous immune-supportive components in shiitake mushrooms are its polysaccharides. (Polysaccharides are large-sized carbohydrate molecules composed of many different sugars arranged in chains and branches.) Although many fungi are well-known for their polysaccharides, no single fungus has been more carefully studied than the shiitake mushroom. We know that this fungus is unique in its variety of polysaccharides, and especially its polysaccharide glucans. (Glucans are polysaccharides in which all of the sugar components involve the simple sugar glucose.) Among the glucans contained in shiitake mushroom are alpha-1,6 glucan, alpha-1,4 glucan, beta-1,3 glucan, beta-1,6 glucan, 1,4-D-glucans, 1,6-D-glucans, glucan phosphate, laminarin, and lentinan. Shiitake mushrooms also contain some important non-glucan polysaccharides, including fucoidans and galactomannins. The immune-related effects of polysaccharides in shiitake mushrooms have been studied on laboratory animals under a wide variety of circumstances, including exercise stress, exposure to inflammation-producing toxins, radiation exposure, and immunodeficiency.
Lentinan, a common extraction of Shiitake used for medicinal purposes, was researched with regard to its immune regulatory applications in individuals living with HIV. In 1998, the Journal of Medicine (AIDS Activities Division, San Francisco General Hospital) conducted a double-blind placebo control trial on 98 patients with HIV. Patients were administered either 2, 5, or 10 mg of Lentinan or placebo via intravenous (I.V.) once a week for eight weeks. Side effects of the I.V. administered Lentinan were generally mild when administered over a 30-minute period. The patients in the study receiving Lentinan demonstrated a trend toward increases in CD4 cells (the white blood cells targeted for destruction by HIV), and in some patients, increased neutrophil (the primary white blood cell involved in the response to infection) activity.
Recent studies have shown that shiitake mushrooms can help protect us against cardiovascular diseases (including atherosclerosis) by preventing too much immune cell binding to the lining of our blood vessels. In order for immune cells and other materials to bind onto our blood vessel linings, certain protein molecules--called adhesion molecules--must be produced and sent into action. By helping to block the adhesion molecule production process, substances in shiitake mushrooms can help protect our blood vessels.
A final basic area of cardiovascular benefits involves antioxidant support. Chronic oxidative stress in our cardiovascular system (ongoing, oxygen-based damage to our blood vessel linings) is a critical factor in the development of clogged arteries (atherosclerosis) and other blood vessel problems. One of the best ways for us to reduce our risk of chronic oxidative stress is consumption of a diet rich in antioxidant nutrients. Shiitake mushrooms are a very good source of three key antioxidant minerals: manganese, selenium, and zinc. They also contain some unusual phytonutrient antioxidants. One of the best studied is ergothioneine (ET). This unique antioxidant is derived from the amino acid histidine, although it's unusual since it contains a sulfur group of molecules that are not present in histidine itself. In studies on ET and our cells' oxidative stress levels, one fascinating finding has been the special benefits of ET for cell components called mitochondria.
Medicinal extracts from shiitake mushrooms have been studied much more extensively than the whole food itself. In cell and laboratory animal experiments, numerous components of shiitake mushrooms have been show to help block tumor growth, sometimes by triggering programmed cell death (apoptosis) in the cancer cells. These components have been collectively referred to as "anti-tumor mycochemicals" provided by shiitake mushrooms. Researchers have speculated that more than 100 different types of compounds in shiitake mushrooms may work together to accomplish these anti-tumor results. While the unique polysaccharides in shiitake mushrooms were first thought to be its primary anti-cancer compounds, scientists are now convinced that shiitake provides many non-polysaccharide substances that have anti-tumor effects.
The special combination of antioxidants found in shiitake mushrooms together with their highly flexible support for immune system function make them a natural candidate for providing us with protection from a variety of problems involving oxidative stress and immune function. This includes rheumatoid arthritis (RA), an area that has begun to interest shiitake mushroom researchers. Although research in this area is preliminary, we expect to see large-scale human studies confirming the benefits of shiitake mushrooms for prevention of RA.
Medicinal extracts from shiitake mushrooms have well-documented effects on a variety of micro-organisms, including bacteria, fungi, and viruses (including human immunodeficiency virus-1, or HIV-1). While we have yet to see large-scale human studies on whole food intake of shiitake mushrooms and decreased susceptibility to colds, flu or other problems related to unwanted activity of micro-organisms, this is a very likely area for future food research and discovery of health benefits.
Preparing and Cooking
The polysaccharides in log-grown shiitakes are readily available to the body, but sawdust-grown mushrooms may not have sufficient density to be absorbed and used as effectively.
The hardwood logs organically and naturally provide all the nutrients that make the shiitake prized as a gourmet mushroom and a health food. Japanese consumers pay less than $4.00 a pound for sawdust-grown shiitakes, but will give $40 a pound and more for log-grown.
Most shiitakes available in the supermarket are grown on sawdust. The log-grown shiitakes go primarily to chefs and pharmaceutical companies. Consumers, who are not aware of the difference, are currently paying the same amount for both types, even though the wholesale price of sawdust-grown shiitakes is about half that of log-grown shiitakes.
Some sawdust-grown shiitakes are very good and many people can't recognize the difference until they have seen both types and cooked with them. Log-grown shiitakes have a meatier texture and will vibrate when shaken. The gills on log-grown shiitakes and on high-quality sawdust-grown mushrooms will be pure white and unbroken. A package of natural shiitakes will usually contain mushrooms of different colors, shapes, and sizes, and the mushrooms will have short stems. The mushrooms from artificial logs may all have the same conical shape, pale color and markings (or no markings). Low-quality sawdust-grown mushrooms with bulbous stems, yellow, broken gills and an ammonia-like smell should be avoided.
Mushrooms are very porous, so if they are exposed to too much water they will quickly absorb it and become soggy. Therefore, the best way to clean mushrooms without sacrificing their texture and taste is to clean them using minimal, if any, water. To do this, simply wipe them with a slightly damp paper towel or kitchen cloth. You could also use a mushroom brush, available at most kitchenware stores.
It is easy to make traditional Shiitake dashi (Japanese mushroom soup stalk). Just add 18-20 dried Shiitake mushrooms and a strip of kombu (kelp) to 8 cups of water. Let the mixture sit until the water darkens and the mushrooms become completely soft. Now you can use the rehydrated Shiitake’s for other dishes and the stalk can be used for anything from soup stalk to risotto stalk.
Another method to cook is to heat 3 TBS of broth over medium heat in a stainless steel skilled. When broth begins to steam add sliced mushrooms and Healthy Saute for 7 minutes. It is best to stir constantly for the last 4 minutes of cooking. Toss with our Mediterranean Dressing and your favorite optional ingredients.