Paul Stamets and the Mycelium Debate — What Measurement Settles
Paul Stamets is the mycologist who brought medicinal mushrooms into mainstream conversation — a TED talk watched by millions, a central role in Fantastic Fungi, dozens of patents, and peer-reviewed research in Scientific Reports. He is also at the center of the industry’s sharpest dispute: whether mycelium grown on grain is a “mushroom.” That argument has run for years because it is fought over definitions. A label ends it with numbers.
Key points
- You cannot discuss medicinal mushrooms without Stamets. He moved the field from the fringe to the mainstream, and mycelium research he led was published in a peer-reviewed journal with a real, measured result.
- The industry dispute is not “who is right about mushrooms.” It is a labeling question: when you buy “mushroom,” how much of what is in the jar is fungal tissue and how much is the grain the mycelium grew on.
- Both sides make claims that can be measured. One side published numbers; the other holds that β-glucan testing is not reliable enough to print on a label.
- Alpha-glucan is the number that ends the argument. It is the starch marker, its measurement is among the oldest and least contested in food chemistry, and it tells you how much grain is in the bottle — without having to settle the definitional debate at all.
Reishi fruiting bodies, at harvest on our farm. The debate this page describes is precisely about what reaches the bottle — this material, or the substrate the mycelium grew on.
Who is Paul Stamets, and why is his name in every mushroom conversation?
Paul Stamets is an American mycologist, founder of Fungi Perfecti and of the supplement brand Host Defense, and to a large degree the person who made fungi a subject discussed outside the laboratory. His 2008 TED talk on six ways mushrooms can save the world has been watched millions of times, and he is the central figure in the 2019 documentary Fantastic Fungi.
His background is real and documented: a graduate of The Evergreen State College, holder of an honorary doctorate from the National University of Natural Medicine, and holder of dozens of mushroom-related patents. He has also published peer-reviewed research rather than only talking about it. In 2018 Scientific Reports published a paper on which he is first author, with researchers from Washington State University and the USDA, finding that extracts from the mycelium of polypore fungi reduced viruses in honey bees. Colonies fed Ganoderma resinaceum extract showed a 79-fold reduction in deformed wing virus and a 45,000-fold reduction in Lake Sinai virus compared with controls.
We say this at the top rather than the bottom, because much of what is written about this controversy online opens with an attack. Stamets broke the ground. Even someone who disagrees with him on one specific question owes him the existence of the field.
What is the mycelium versus fruiting body debate actually about?
The mushroom you recognize — cap and stem — is the fruiting body. Mycelium is the thread network the fruiting body grows from. Both are the same organism, but they are not the same material. The industry dispute is not about that biology. It is about what happens when mycelium is grown on grain and the result — mycelium together with the grain it grew on — is sold under the word “mushroom.”
In the production method common in the United States, called mycelium-on-grain, the mycelium grows through brown rice or another grain. At the end of the process the threads and the kernel cannot be separated; they are physically interwoven. So the whole mass is milled together. What gets weighed and packed is a mixture of fungal tissue and substrate — and in most cases the buyer sees nothing on the label indicating how much of it is which.
That is the background to everything that follows. If you want the baseline version of the distinction without the politics around it, we wrote it separately: Fruiting body or mycelium — what to check on the label.
What does the Stamets side argue?
That mycelium is part of the organism, and therefore the word “mushroom” applies to it. On this view, “mushroom” describes the whole organism, while “mycelium” and “fruit body” name distinct parts within it — exactly as one says “plant roots,” “plant seeds” and “plant flowers” without anyone claiming these are different plants.
The argument also has a practical side, and that deserves a fair hearing too. Host Defense holds that the fermented substrate is a functional part of the formula rather than a filler, and that the mycelium itself is immunologically active. Their stated logic is to keep the mushroom’s natural chemical architecture intact as a whole, rather than isolating or concentrating any single compound out of it.
In June 2023, Fungi Perfecti — together with M2 Ingredients, Gourmet Mushrooms and Monterey Mushrooms — published a joint open letter arguing that the regulatory petition filed against their category obscures and misrepresents well-established mycological definitions. That is a substantive claim, not a slogan: in the mycological literature “mushroom” is indeed sometimes used for the organism as a whole.
What does the other side argue — and what happened at the FDA?
The other side, led by Jeff Chilton of Nammex, does not claim mycelium is biologically not fungal. It makes a labeling claim: that a product which is mostly grain is sold under a name implying it is mostly mushroom, without disclosing that grain was added. On June 7, 2023, a formal citizen petition was filed with the FDA on exactly this point (docket FDA-2023-P-2340).
The petition asks for two straightforward things: that fungal ingredients be listed by the fungal part they come from and by the specific species, and that added grain ingredients be disclosed. In December 2023 the FDA issued a 180-day interim response — meaning it had not reached a decision, citing competing agency priorities — and as of this writing no final decision has been issued.
One thing that usually goes unsaid should be said plainly here: Nammex is a commercial supplier of fruiting-body raw material. It has a financial interest in the outcome. That does not make its data wrong, but it does mean the data should be read the way any figure published by a party who benefits from it should be read.
Why has this argument not been settled in years?
Because it is fought over definitions, and definitions cannot be measured. If the question is “is mycelium a mushroom,” both sides can argue forever: both cite mycology, both are partly right, and no laboratory test on earth will decide between them. The question is built so that it cannot be resolved.
But a second question hides underneath it, and it is the one that actually matters to whoever is paying: how much of the material in this jar is fungal tissue, and how much of it is grain? That second question is not definitional. It is quantitative, and it has a numerical answer.
This is where the debate ends for us. We do not vote in the American controversy and we are not trying to decide who owns the correct definition of the word “mushroom.” We answer the second question and leave the first one to linguists.
What does the measurement actually show?
Two numbers, not one. Beta-glucan is the active polysaccharide that comes from the fungal cell wall. Alpha-glucan is starch — and in a mushroom product it is essentially a marker for how much grain stayed in. Measure both in the same assay and the product’s profile is exposed without having to believe either side of the argument.
The 2016 Nammex white paper, presented that year at the ISMS conference, published tests on commercial products. Two findings from it illustrate the gap well: one mycelium-on-grain product measured 66.4% alpha-glucan against 3.2% beta-glucan, and another identified as mycelium-on-grain measured 72.5% alpha-glucan against 1.3% beta-glucan. In other words: more than two-thirds starch, and low single digits of the compound the product was bought for.
| What is measured | What it means | Why it settles the argument |
|---|---|---|
| Beta-glucan | The polysaccharide from the fungal cell wall — the compound studied in the immune literature. | A high number cannot come from grain. It can only come from fungal tissue. |
| Alpha-glucan | Starch. Mushroom fruiting bodies contain very little; grain contains a great deal. | It is the direct measure of how much substrate remained in the product. You do not need to know what happened in production. |
| “Total polysaccharides” | A figure that pools both together, and sometimes other sugars and carriers as well. | It does not distinguish an active compound from starch — so it settles nothing. |
The distinction between those three rows is the whole story, and we expanded on it separately: Beta-glucan vs “polysaccharides” — the number that decides.
Is Host Defense’s objection to beta-glucan testing justified?
Partly — and the part that is justified deserves to be said out loud. The company’s stated position is that the industry has no single standard, validated methodology for measuring beta-glucan, and that common assays detect mainly soluble beta-glucan while the insoluble fraction goes undetected. Printing a percentage on a label would therefore, in their view, be misleading. In its place they publish a guarantee of more than 55% polysaccharides.
The methodological objection itself is not trivial: a beta-glucan result does depend on the hydrolysis method used, and different methods return different values. But the answer to it was published in the very year the dispute erupted. In 2016, McCleary and Draga published a dedicated method for measuring beta-glucan in mushrooms and mycelial products in the Journal of AOAC International — the journal of the organization whose work is validating analytical methods. The method measures total glucan by controlled acid hydrolysis, measures alpha-glucan separately using enzymes, and derives beta-glucan as the difference. The same authors compared several hydrolysis approaches and published which one performs best. This is not an improvised assay; it is the one that became the industry reference.
Here is the point that makes the entire methodological discussion secondary: the objection applies to beta-glucan, not to alpha-glucan. Starch measurement is among the oldest and best-established assays in food chemistry, and it is not contested. So even someone who accepts every reservation anyone has about the reliability of a beta-glucan figure can still ask how much starch is in the product — and get an answer whose measurement no one disputes. And that is exactly the question that reveals how much grain went into the bottle.
It should also be said that “more than 55% polysaccharides” is a figure that does not distinguish beta-glucan from starch, because both are polysaccharides. It reports a broader category, and therefore does not answer the question under dispute. That is an observation about what the number measures, not about the intentions of whoever published it.
So is mycelium worthless?
No, and this is where most writing on the subject overshoots. Mycelium is living fungal tissue with its own chemistry, and Stamets’ own 2018 research is a good demonstration: mycelium extracts reduced viruses in bees to a measured and substantial degree, in a peer-reviewed journal. Mycelium is not a fake. It is a different material.
The problem was never the mycelium — it was the grain nobody mentioned. A mycelium product grown in liquid culture and harvested without substrate is a perfectly legitimate mycelium product; it can be named accurately, measured, and sold. A product in which mycelium and grain are milled together and sold as “mushroom” without stating the ratio is an entirely different question, and it is not a mycological one. It is a disclosure question.
For complete fairness, one more thing: the 2018 bee paper carries a conflict-of-interest declaration in its own text — Stamets holds patents in the field, and Washington State University received a research grant from Fungi Perfecti. We note this not to discredit the research; such a declaration is exactly what sound science requires be published. We note it to stay consistent: we ask readers to weigh data alongside the interests of whoever published it, so we apply that rule even when it is inconvenient for the side we happen to agree with.
How often do mushroom supplement labels actually match the contents?
Less often than buyers assume, and that is measurable rather than rhetorical. A 2017 study in Scientific Reports examined 19 batches of reishi supplements purchased in the United States and compared the bioactive components actually measured against what the labels claimed. Only five of them — 26.3% — were found to be in accordance with their labels.
That is a regulated market, and that is what was measured in it. The practical conclusion is simple: do not buy on the strength of the story on the back of the box. Ask for the numbers. If you want the detailed version, we wrote a guide to reading a mushroom supplement test report that walks through a real report line by line.
Where we stand — and why you should check us too
We grow and sell fruiting-body extracts, so we have an obvious commercial interest in one side of this debate. That is precisely why we do not ask you to take our word for it: we publish the full external laboratory report for each extract, with a certificate number you can verify against the lab.
Our extracts were tested at TÜV Austria and measured in the range of 23.21%–28.16% beta-glucan, on the dry-matter basis of the finished extract. The assay is the Megazyme enzymatic method — from the same house that produced the method published in the Journal of AOAC International referenced above. And in those same tests, alpha-glucan was not detected. That is the part that matters most in the context of this page: the absence of starch is chemical proof that no grain went in.
| What was measured | Beta-glucan 1,3/1,6 and alpha-glucan |
|---|---|
| Laboratory | Tested at TÜV Austria |
| Result | 23.21%–28.16% beta-glucan, dry-matter basis of the extract |
| Alpha-glucan | Not detected |
| Starting material | 100% fruiting bodies, no grain substrate at any stage |
We will add our own caveat too, because a page that demands disclosure from others owes it to itself: the beta-glucan percentage is measured on the finished extract, on its dry-matter basis, not on the raw mushroom. It does not tell you how many milligrams are in a serving — that calculation requires extraction-yield data we do not publish, so we do not publish its result either. All of our laboratory reports are open, and each report shows which extract was tested.
How do you decide for yourself, without picking a camp?
Three questions, in this order, all about the label rather than the story. Which part of the fungus is in the product. What the beta-glucan percentage is, and who measured it. And what the alpha-glucan percentage is — because that is the question that reveals grain, and the one least often asked.
| What to ask | An answer you can check | An answer you cannot check |
|---|---|---|
| Which part of the fungus? | “Fruiting body” or “mycelium,” stated explicitly on the label. | “Mushroom” with no part named, or “whole organism.” |
| What is the beta-glucan percentage? | A number, the name of the lab, and the measurement basis. | “Rich in beta-glucans,” or a percentage with no source. |
| What is the alpha-glucan percentage? | A number, or “not detected,” in a report you can see. | Silence. This is the most common answer. |
| What is the extraction ratio? | A numeric ratio, and the basis it was measured on. | “Concentrated” or “strong extract.” |
If the answers in the middle column exist, the definitional argument no longer concerns you. You know what you bought. And if you want to go deeper on extraction ratios — a number that is unusually easy to mislead with — we wrote about that in what an “extraction ratio” really means.
Fruiting-body extracts only — with the lab report published
Every extract we sell is made from fruiting bodies grown on our farm in the Galilee, and its external test report is published in full — including the alpha-glucan line.
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The bottom line
Paul Stamets broke the ground, and no one can write about medicinal mushrooms without acknowledging it. The argument he sits at the center of has run for years because it is phrased as a definitional question — “is mycelium a mushroom” — and definitional questions are not settled in a laboratory. But the question that actually matters to whoever is paying is a different one, and it is measurable: how much of the material in the bottle is fungal tissue, and how much is the grain it grew on. Beta-glucan and alpha-glucan, side by side on the same report, answer it. We are not a party to the American controversy. We simply publish both numbers, and ask every brand to do the same.
Frequently asked questions about Paul Stamets and the mycelium debate
Who is Paul Stamets?
An American mycologist, founder of Fungi Perfecti and of the supplement brand Host Defense. A graduate of The Evergreen State College, holder of an honorary doctorate from the National University of Natural Medicine, and holder of dozens of patents. He is best known for his 2008 TED talk and his central role in the 2019 documentary Fantastic Fungi.
What is the controversy around Host Defense?
Its products are based on mycelium grown on fermented brown rice, milled and packaged together with the substrate. The controversy is not about biology but about labeling: whether it is accurate to sell a mixture of mycelium and grain under the word “mushroom” without stating the ratio between them.
Is mycelium a mushroom?
It depends what is being asked. Biologically, mycelium is part of the same organism, and that is a legitimate position in mycology. From a consumer standpoint the question is different: mycelium grown on grain arrives in the jar together with that grain, so the product’s composition differs materially from a fruiting-body extract.
What is the Nammex FDA petition?
A citizen petition filed on June 7, 2023 (docket FDA-2023-P-2340) by Nammex, led by Jeff Chilton. It asks that fungal ingredients be labeled by fungal part and species, and that added grain be disclosed. The FDA issued a 180-day interim response in December 2023 without reaching a decision.
Why doesn’t Host Defense publish a beta-glucan percentage?
Per its stated position, the industry lacks a standard validated measurement method and common assays detect mainly soluble beta-glucan. Instead the company publishes a guarantee of more than 55% polysaccharides — a figure that does not distinguish beta-glucan from starch, since both are polysaccharides.
What is alpha-glucan and why does it matter here?
Alpha-glucan is starch. Mushroom fruiting bodies contain very little of it; grain contains a great deal. A high alpha-glucan percentage in a mushroom product therefore indicates grain substrate that stayed in. Starch measurement is an old, well-established assay, so it is decisive even for someone who doubts the reliability of beta-glucan testing.
Is mycelium worthless?
No. Mycelium is fungal tissue with its own chemistry, and research Stamets led in 2018 showed that mycelium extracts reduced viruses in honey bees. The problem is not the mycelium — it is the grain sold alongside it without being mentioned.
What was measured in Triterra’s extracts?
Testing at TÜV Austria measured 23.21%–28.16% beta-glucan on the dry-matter basis of the finished extract, with alpha-glucan not detected. The extracts are made from fruiting bodies only, with no grain substrate at any stage. All of our lab reports are open.
Sources
- McCleary BV, Draga A. Measurement of β-Glucan in Mushrooms and Mycelial Products. Journal of AOAC International. 2016;99(2):364-73. View on PubMed
- Stamets PE, Naeger NL, Evans JD, et al. Extracts of Polypore Mushroom Mycelia Reduce Viruses in Honey Bees. Scientific Reports. 2018;8:13936. View on PubMed
- Wu DT, Deng Y, Chen LX, et al. Evaluation on quality consistency of Ganoderma lucidum dietary supplements collected in the United States. Scientific Reports. 2017;7:7792. View on PubMed
- Anaya EU, et al. Dectin-1 multimerization and signaling depends on fungal β-glucan structure and exposure. Biophysical Journal. 2023. View on PubMed
- Zhang X, et al. Edible mushroom polysaccharides: structural characteristics, chemical modification strategies, and structure-activity relationship: a review. International Journal of Biological Macromolecules. 2025. View on PubMed
- U.S. Food and Drug Administration — Citizen petition docket FDA-2023-P-2340 (Nammex), filed June 7, 2023
- Fungi Perfecti — Open letter in response to the Nammex citizen petition, June 20, 2023
- Nammex — Redefining Medicinal Mushrooms — the white paper and its commercial product testing
Continue reading
- Fruiting body or mycelium — what to check on the label
- Beta-glucan vs “polysaccharides” — the number that decides
- How to read a mushroom supplement test report (COA)
- What an “extraction ratio” really means
- Fresh or dried mushroom — what actually goes into the extract
- Full lab results — beta-glucan, heavy metals and pesticides
- All extracts
These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease. This page is educational and describes an industry labeling debate; it is not medical advice. Consult a qualified healthcare professional before using any supplement, particularly if you are pregnant, nursing, or taking medication.
