Shiitake Mushrooms

Health Benefits
(Source: World's Healthiest Foods, George Mateljan)

Unique Nutrient Benefits from Shiitake Mushrooms

When thinking about the health benefits of shiitake mushrooms, it's worth remembering that this food does not belong either to the plant family or to the animal family but to its own separate group of life forms known as fungi. (From a science perspective, shiitake mushrooms are classified as "macrofungi" since they are large compared with other microorganisms and can easily be seen without the help of a microscope.) In some ways, fungi like shiitake mushrooms are actually closer to animals than to plants because they can synthesize glycogen (a storable form of starch) in the same way as animals. This feature of fungi often provides them with many unique nutrients in the carbohydrate category. In addition, because shiitake often make their home on hardwood trees, they have special enzyme systems for breaking down wood components, and these systems also provide them with unique nutrient features. The chart below summarizes some of the better-studied unique nutrients in shiitake.

(milligrams per 100 grams of food)

Name of SubstanceNutrient Categorybeta-glucanspolysaccharidescarvacrolmonoterpenoid-derived phenolscopalic acidditerpenoidsergothioneineamino acid derivativeseritadeninealkaloidslentiavidinsproteinslentinanspecific member of the beta-glucan polysaccharides

Among the nutrients listed above, lentinan and its fellow beta-glucans have received special research attention. These unique polysaccharide nutrients have been shown to have antioxidant and anti-inflammatory properties, within the digestive tract, within the bloodstream, and in whole body metabolism involving a variety of different body systems. While we will be addressing more specifics about this unique list of nutrients and their health benefits in the paragraphs below, we wanted to make sure that this particular collection of nutrients was seen for what it is: a unique and remarkable group of substances that provides many of the core health benefits from shiitake.

Antioxidant and Anti-Inflammatory Benefits from Shiitake Mushrooms

If we look only at conventional nutrients found in shiitake mushrooms, we can see impressive antioxidant benefits. As mentioned earlier, shiitake are our 4th best source of the antioxidant mineral copper at WHFoods. They are also our 4th best source of another antioxidant mineral—zinc. And this list of antioxidant minerals does not stop with zinc. Shiitake are also our 7th best source of the antioxidant mineral selenium. While you could get a higher-ranked source of selenium by choosing many of our fish, these foods drop down below shiitake mushrooms on our list of high-ranked zinc sources. Similarly, you could get a higher-ranked source of zinc by choosing beef from our WHFoods, but beef is far below shiitake mushrooms on our list of copper sources. So, it makes sense to think about shiitake mushrooms as a quite unusual source of multiple antioxidant minerals.

It's the more unusual nutrients in shiitake mushrooms, however, that provide this food with its antioxidant "claim to fame." For example, multiple studies have linked broad antioxidant and free-radical scavenging activity with intake of shiitake mushrooms due to their high beta-glucan content. Also interesting in this context are studies that have found a greater degree of antioxidant activity to be associated with polysaccharides from shiitake mushrooms that contain disproportionally high amounts of the sugars rhamnose and mannose. Alongside of their glucan content, shiitake mushrooms are known to provide us with phenolic antioxidants (like ferulic and capolic acid), and terpene-related antioxidants like carvacrol.

On the anti-inflammatory front, a growing number of studies have shown reduction in inflammation-related events following intake of shiitake mushrooms. As mentioned earlier in this profile, consumption of shiitake mushrooms in one recent study was determined not only to lower blood levels of the inflammatory messaging molecule MIP-1alpha (macrophage inflammatory protein 1alpha), but also to raise blood levels of anti-inflammatory molecules including interleukin-4 and -10, and interleukin-1alpha (IL-4, IL-10, and IL-1a). Additionally, many of the phenolic acids provided by shiitake mushrooms have been determined to provide anti-inflammatory benefits.

Other Potential Health Benefits from Shiitake Mushrooms

In many areas of decreased disease risk—including risk of certain cancers, cardiovascular diseases, immune system problems, and type 2 diabetes—we have pieces of evidence (often from lab studies on cell cultures or from studies on mice or rats) about the likely role played by shiitake mushroom intake in helping to prevent chronic disease. However, most of these studies involve either purified components from shiitake mushrooms or shiitake mushroom extracts rather than dietary intake of these mushrooms in whole food form. For all of the reasons above, we have referred to research in the areas described below as demonstrating potential health benefits, and we look to future studies to confirm these benefits for people who enjoy eating shiitake mushrooms in food form in their diet.

Potential immune system benefits from shiitake mushrooms have been a focus in recent studies involving an immune-related messaging molecule called interleukin-23 (IL-23). IL-23 is one of the messaging molecules produced by the immune system's dendritic cells. A key role of our dendritic cells is to help process potentially allergenic or harmful substances and present them to other immune cells for neutralization. In animal studies, intake of shiitake mushroom extracts has been shown to increase IL-23 levels, and by increasing these levels, they also help to improve the recognition of potentially allergenic or harmful substances, particularly in the lower part of the digestive tract. Researchers believe that this ability of shiitake mushrooms to improve gut immunity may also apply to humans who consume shiitake mushrooms in whole food form and ordinary amounts.

Two other substances in shiitake mushrooms that seem important to mention in this immune system context are conjugated linoleic acid (CLA) and ergothioneine, a sulfur-containing derivative of the amino acid histidine. Both of these substances have been shown to have immune-related properties and are regarded as providing immune support.

Numerous lab studies on cancer cell lines have shown the ability of shiitake mushroom extracts to inhibit tumor growth. Researchers have also linked the unique polysaccharide content of shiitake mushrooms to these tumor-inhibiting results. To date, potential benefits of shiitake mushrooms for reduced risk of colon cancer have been a primary area of interest, but we expect to see other types of cancer investigated in this context as well.

An area of strong shiitake mushroom interest that partially overlaps with investigation of cancers involves the role of microorganisms in promotion of chronic inflammation and subsequent elevation of cancer risk. Unwanted overgrowth of certain microorganisms can cause chronic inflammation and infection; through these processes, they can increase cancer risk. Countering this type of risk are some of the unique sulfur compounds found in shiitake mushrooms, which have been shown to possess antiviral, antibacterial, and antifungal properties. These antimicrobial properties in shiitake mushrooms may turn out to play an important role in the cancer-preventing potential of this food.

As mentioned earlier in this profile, researchers know that eritadenine—a purine-based alkaloid in shiitake mushrooms—is able to reduce activity of an enzyme related to regulation of blood pressure known as ACE (angiotensin-converting enzyme). When ACE is fully active, our blood vessels become constricted, and this constriction gives our blood less space in which to flow; as a result of this, our blood pressure increases. By blocking ACE activity, the eritadenine in shiitake mushrooms helps achieve the opposite effect: blood vessel constriction is prevented, our blood vessels maintain a wider diameter providing for more space for our blood to pass through, and an increase in our blood pressure is prevented. Not surprisingly, many researchers conclude that shiitake mushrooms provide us with cardiovascular support through improved regulation of blood pressure.

Also important on this cardiovascular front are the unique sulfur compounds present in shiitake mushrooms. Shiitake mushrooms appear to have their own unique sulfur-metabolizing enzyme that falls into the category of enzymes known as the "cysteine desulfurases." These enzymes are responsible for taking the sulfur in cysteine amino acids and helping incorporate it into other metabolic activities. These unique sulfur-related metabolic activities in shiitake mushrooms have been linked to several different aspects of cardiovascular function, including the degree to which our platelet cells clump together (or "aggregate") in our blood stream. In general, studies on shiitake show a potential for better control of platelet aggregation when shiitake mushroom extracts are included in the diets of lab animals.

Improved regulation of blood sugar levels and insulin secretion has been a research finding in multiple animal studies involving consumption of shiitake mushroom extracts. While many components of shiitake mushrooms may contribute to these helpful effects, it should not be surprising that these mushrooms can be helpful for controlling our blood sugar. Shiitake mushrooms is a good source of fiber and provides us with 1.5 grams for only 51 calories. We also know that many shiitake mushroom polysaccharides do not get broken down in our upper digestive tract, so their simple sugars do not get released for absorption up into our bloodstream. Both of these factors point to a food that would be helpful in blood sugar regulation. However, it will take large-scale studies on human participants consuming shiitake mushrooms in their routine diet to determine whether intake of this food is a reliable way to lower our risk of type 2 diabetes or related health problems.

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