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Fruiting Body versus Mycelium: a misguided debate
Dennis E. Desjardin, PhD.
Chief Mycologist, Sempera Organics
Professor Emeritus, San Francisco State University
There is a brewing controversy in the supplements and nutraceutical industry over which fungal structure provides the best nutritional and medicinal value: mushroom fruitbodies or mycelium (Rogers 2016). Some commercial producers of fungal nutraceuticals and food supplements report that only mushroom fruitbodies provide substantial nutritional and medicinal benefits, while others argue that the mycelium provides equal benefits. We believe that both components of the life cycle of functional fungi produce compounds of nutritional and medicinal value, and that it is important to understand the contributions of both structures to health and well-being.
To address the issue of mushrooms versus mycelium, let’s begin by learning about each of these components of a mushroom’s life cycle. The major cellular structure of every filamentous fungus is a hypha (pl. hyphae). This is a chain of cylindrical cells that is usually branched and grows from its terminal cells. It forms most of the biomass of an individual, and its function is to exploit its surroundings for nutritional resources to support its growth and development. Collectively, the hyphae are called mycelium. All fungi are heterotrophs, organisms that must obtain their nutrition from other organisms—they need to feed. The mycelium is this feeding component of a mushroom’s life cycle, absorbing and forming many different molecules to support its metabolism, allowing it to breakdown complex polysaccharides, proteins, and fats into smaller molecules that it uses for its own growth and development. Medicinal mushroom species are saprotrophs (decomposers) or pathogens, and feed on dead or living organisms. Their mycelium must have the appropriate complex of molecules that allow it to obtain nutrition from other organisms, as well as protect itself from predation. The mycelium is the business phase of the individual—forming a complex array of filaments that invades its substrate, consuming what it needs while combating competitors and evading predators. Over millions of years of evolution, fungi developed various metabolic pathways to produce unique compounds needed to overcome these challenges. Mycelium can live for months, years, centuries and even millennia in nature, as long as there is available water, nutritional resources and suitable environmental conditions. Imagine this mycelium as a huge network of tiny filaments growing through the soil, through a dead log, or inside an unwitting insect larva, in search of organic material to feed on. The majority of an individual fungus’s life is spent in this mycelial phase, feeding, growing, expanding its territory, and recycling organic matter. But in order for most fungal species to survive locally, they must reproduce.
Many medicinal fungi reproduce by forming mushrooms, i.e., fruitbodies. A mushroom is the sexual reproductive structure that develops from the mycelium. For the fungus, the sole function of a mushroom is to produce spores for reproduction and dispersal. They are designed to optimize surface area for spore production, coordinated with structural design for efficient and effective spore dispersal. At the proper time, when environmental conditions and resources are appropriate, the mycelium will form primordia, which develop into mushrooms, maturing over hours, days or weeks depending on the species. The entire mushroom is formed from hyphae, just like its mycelium. The resources mushrooms need for differentiation, growth and development come from its mycelium. Most nutrients are stored in the mycelium and are shuttled through the hyphae to the primordia and developing mushrooms. The genome of a mushroom is identical to that of the mycelium from which it develops because it represents the same individual. The types and amounts of compounds the hyphae produce may vary depending on age, hyphal location, cell function, mineral and gas availability, temperature, pH, and other factors.
Mushrooms and mycelium have two distinctly different yet complementary functions, one for reproduction and dispersal, the other for growth and resource acquisition and exploitation, respectively. Given their different roles in the life cycle, do these structures have different types and concentrations of compounds which may be of nutritional and medicinal value to humans? That is a question without a simple answer, because it depends on the compounds of interest, the species involved, growth conditions (natural versus artificial), substrate type, and how they are harvested and processed (fresh, dried, powders, extracts). It is well established that the concentration of nutritional and medicinal metabolites found in fruit bodies and mycelia varies widely based on the types of substrates the mycelia utilize, the conditions under which they are grown, strain selection, developmental stage, and ecological interactions (Lavelli et al. 2018, Berger et al. 2022). This variability is undoubtedly the result of the high adaptive abilities of functional fungi to survive in their natural habitats.
To get a better understanding of the current state of knowledge of mushroom fruitbody and mycelium metabolites, let’s look at a few case studies of common medicinal fungi that address pertinent questions.
ß-glucans, polymers of glucose subunits with ß-1,3 and ß-1,6 linkages that form much of the cell walls of fungi, have received focused attention because of there validated immunomodulatory and anti-inflammatory activities (Cerletti et al. 2021). They are also at the core of the mushroom versus mycelium controversy.
Do mushroom fruitbodies contain more ß-glucan than their mycelium?
Case Study – Lentinula edodes – Shiitake. When comparing the ß-glucan content of medicinal mushrooms, the major paper cited by proponents of mushrooms versus mycelium, viz., Bak et al. 2014, is based on an analysis of ten Korean cultivars of Lentinula edodes, the shiitake mushroom. In this research, the mushrooms were grown on wood, separated into pileus and stipe portions, dried, pulverized and used in the analyses; whereas mycelium from the ten strains was grown on potato dextrose agar for 30 days, scraped off the agar, dried, pulverized and used for comparison with the mushroom fruitbody powder. First, note that the substrates on which the two test groups were grown are substantially different, wood versus PDA media, indicating that the nutritional resources the strains were provided was not the same in both test groups. This will directly impact the quality and quantity of polysaccharides produced by the fungi in each test group. The authors explicitly note that their data on the ß-glucan content of mushroom fruitbodies differ from other researchers, and speculate that the discrepancy could be due to the “shiitake mushrooms strain types used, growth conditions, degree of fruiting body maturity, use of whole fruiting bodies vs. separate section (pileus, stipes), or the use of fresh vs. dried fruiting bodies.” In addition, they note other differences in composition between studies may be due to differences in the type of substrate used. Hence, total ß-glucan content of shiitake mushrooms is not constant across studies conducted by different researchers on different strains of mushrooms, when comparing fruitbodies to fruitbodies. Their strains ranged from 20.06–44.21% total ß-glucans in pileus [calculated as percentage (w/w) of mushroom dry weight], and 32.51–56.47% in stipe, whereas other published data ranged from 20–41.2%.
But what about total ß-glucan content of mycelium? In Bak et al. (2014), the mean ß-glucan content of the mycelium amongst all ten strains was 22.23%, lower than that of the pileus (mean 35.93%) and stipe (mean 44.33%), supporting the contention that shiitake fruitbodies contain more ß-glucan than does mycelium. However, a closer look at the data indicates that some strains have as much ß-glucan in their mycelium as that found in the fruitbodies of other strains. For example, ß-glucan content of the mycelium of strain Gaeulhyang (27.09%) and strain Soohyangko (26.97%) was comparable to that of the pileus (24.86%) and stipe (29.74%) of strain Dasanhyang. Lastly, in the Bak et al. (2014) paper, the comparison of ß-glucan content in mushrooms grown on wood versus mycelium grown on PDA media is not an equivalent comparison. A fairer comparison would be to test total ß-glucan content of mushrooms grown on a myceliated substrate to that of the myceliated substrate from which they developed, i.e., the same nutritional source for both fruitbodies and mycelium. These data are not available.
What about other bioactive compounds? Do mushroom fruitbodies contain more than their mycelium?
Case Study – Hericium erinaceus (Lion’s Mane, yamabushitake). Lion’s Mane is an edible and medicinal mushroom consumed for hundreds of years in Asia. The mushrooms and mycelium contain bioactive compounds that show strong anti-inflammatory, antioxidant, and immune modulatory activity. Of particular interest are two groups of cyathane diterpinoids, hericenones and erinacines. There are at least ten types of hericenones, formed only in the fruiting bodies, while there are 15 different erinacines produced only by the mycelium. Compounds of both groups are low molecular weight, relatively hydrophobic, and most are small enough to cross the blood-brain barrier (Thongbai et al. 2015). Both hericenones from fruitbodies and erinacines from mycelium stimulate nerve growth factor (NGF) and promote NGF-induced neurite outgrowth in nerve cells in vitro (Lai et al. 2013). Human clinical trials with powdered fruitbodies resulted in the prevention of cognitive impairment in older individuals with mild cognitive impairment (Mori et al. 2009) and improved physical and perceptive capacity in individuals suffering cerebrovascular and neuro-disease (Kawagishi and Zhuang 2008). However, when looking more closely at the constituents causing such effects, hericenones failed to promote NGF gene expression in human astrocytoma cells (Mori et al. 2008), suggesting that other compounds in fruitbodies may be responsible for the observed positive results. To date, only erinacines A and S, not hericenones have been verified to cross the blood-brain barrier, suggesting a greater likelihood that erinacines are responsible for cognitive enhancement (Li et al. 2020). Furthermore, the in vivo neuroprotection of erinacine A-enriched mycelium has been demonstrated in studies against stroke, Parkinson’s disease, depression, and aging (Li et al. 2018). Based on these and other studies, it is likely that erinacine A is one of the key compounds responsible for the neurotrophic and neuroprotective activities of H. erinaceus, and this important bioactive is produced only in the mycelium. Hence, for cognitive enhancement, consumption of mycelium-based products may show more efficacy than fruitbody-based products.
Case Study – Ophiocordyceps sinensis & Cordyceps militaris. The caterpillar fungus, Ophiocordyceps sinensis (aka Dong Chong Xia Cao, yartsa gunbu), is well known in traditional Tibetan and Chinese medicine. Over 30 medicinal bioactivities have been documented, including immunomodulatory, antitumor, anti-inflammatory, and antioxidant, derived from over 20 bioactive ingredients, mainly extracellular and intracellular polysaccharides, fatty acids, cordycepin, adenosine, D-mannitol, and sterols (for a review refer to Lo et al. 2013). The species is a pathogen on larvae of the ghost moth, and fruitbodies grow from the head region of infected, subterranean larvae. Traditionally, the fruitbody as well as the infected larva is used in medicine. Because of rarity and high demand, the whole fungus is extremely high priced, and the species is threatened in its natural habitats. Alternatives to wild collecting have been sought, and artificial cultivation of the mycelium has received a lot of attention. The question then arises, does the mycelium contain the same types and quantities of bioactive ingredients as the wild fruitbody—addressing our topic of which is better, mushrooms or mycelium?
Li et al. (2006) studied the composition of Hirsutella sinensis, the anamorph of Ophiocordyceps sinensis (the asexual phase of the life cycle of this species), comparing natural fruitbodies to mycelium from submerged cultures. Results of their research showed that the mycelium contained higher contents of crude fat, crude protein, total and essential amino acids, the elements calcium, selenium and copper, vitamin B1, and the four nucleosides (adenosine, guanosine, uridine, inosine) than did the natural fruitbodies. The mycelium was lower than the fruitbodies in content of unsaturated fatty acids, iron, zinc, tin, vitamin B6 and niacin. They concluded that mycelium was a probable substitute for natural fruitbodies of O. sinensis. Cordycepin concentration was not studied.
In a study of chemical composition and medicinal value of another insect pathogen, Cordyceps militaris, Chan et al. (2015) found that the mycelium had higher carbohydrate content (39.6%) than the fruitbodies (29.1%), but lower protein (39.5% vs 59.8%) and lower total amino acid content (24.98 mg/g vs 57.29 mg/g) than fruitbodies, respectively. However, when comparing the content of the important bioactive molecules cordycepin and cordycepic acid (D-mannitol), the mycelium had higher concentrations of both, 0.182% cordycepin and 5.2 mg/100g cordycepic acid, than did the fruitbodies, 0.11% and 4.7 mg/100 g, respectively. Additionally, the cordycepin content of C. militaris is higher than that found in fruitbodies of O. sinensis, making the easily artificially cultured C. militaris a good substitute for the rare and endangered O. sinensis (Jedrejko et al. 2021).
Case Study – Lariciformis officianalis (syn. Fomitopsis officianalis). Commonly known as Agarikon, L. officianalis is a pathogenic polypore species that causes brown heart rot of conifers and has been used for centuries in traditional European medicine as effective in treatment of excessive sweating, dizziness, rheumatism, respiratory and digestive diseases, cancer and as an anti-inflammatory agent. In a comparison of bioactive compounds with medicinal value found in mycelium versus mushrooms, Fijalkowska et al. (2020) found higher antioxidant activity, proteolytic activity and indole compounds in the mycelium than in mushrooms of this species. The total content of indole compounds in mycelium extracts was 526.39 mg/100 g.d.w. whereas that from the mushrooms was only 80.83 mg/100 g.d.w., i.e., 6.5 times more. In addition, they found higher levels of ergosterol, specific phenolic compounds, and the minerals zinc, iron and magnesium in the mycelium than in the mushrooms. Ergosterol, important in the synthesis of a bioactive form of vitamin D, showed nearly twice the concentration in the mycelium than in the mushrooms (102.02 mg/100 g.d.w. versus 52.97 mg/100 g.d.w.). Clearly, for many important bioactive compounds, the mycelium of Agarikon may be more beneficial than the fruitbodies.
Case Study – Inonotus obliquus (Chaga) and Lignosus rhinoceros (Tiger Milk Mushroom). Both Inonotus obliquus (Chaga) and Lignosus rhinoceros (Tiger Milk Mushroom) are well-known medicinal polypore mushrooms. However, it is not the fruitbody of the species that is used medicinally, but rather an over-wintering, long-term storage structure known as a sclerotium. The sclerotium is composed entirely on non-sporulating hyphae. In the case of chaga, it rarely forms fruitbodies, and traditionally it is the sclerotia that are collected for medicinal purposes showing major antitumor, antioxidant, anti-virus, hypoglycemic and hypolipidemic activities (Lu et al. 2021). For tiger milk mushroom, there are very few bioactives in the mushroom part of the lifecycle (some report none) but high amounts in the sclerotia, which in clinical trials effectively improved respiratory health, immunity, and antioxidant status (Tan et al. 2021). For these two important medicinal fungi, the argument of mushrooms versus mycelium is baseless.
Case Study – Agaricus subrufescens (Almond Mushroom, syn. A. blazei, A. brasiliensis). The Almond Mushroom, widely cultivated for its medicinal uses and pleasant almond flavor, was recently shown to have more than 10,000 putative genes that were differentially expressed in mycelia, primordia and fruitbodies. Lu et al. (2020) reported that fruitbodies showed a higher activity of genes associated with stress response, ribosome biogenesis, arginine, and steroid biosynthesis, while Fan et al. (2021) reported higher levels of ergosterol in the mycelium versus the fruitbodies.
Unfortunately, few studies have compared the chemical composition of mushroom fruitbodies to that of its mycelium grown under similar conditions, so stating which provides more nutritional and medicinal value, mushroom fruitbodies or mycelium, is disingenuous. From the available published data, it is apparent that both fruitbodies and mycelium produce efficacious compounds (Cohen et al. 2014, Berger et al. 2022). When considering supplements for medicinal and nutritional purposes, what is important is the documentation and standardization of the quantities of bioactive constituents, and that the compounds are derived from both the fruitbodies and mycelium, i.e., a full spectrum resource. This will assure the highest benefits from the suite of medicinal compounds produced by the species of choice.
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