Mushroom Supplement Adulteration
31.6% of products correctly labeled
A 2023 laboratory survey of 120 commercially available mushroom supplements in Italy found only 31.6% correctly labeled for both species identity and active compound content.
Tarsitano et al., Journal of Fungi, 2023
5–7%
average beta-glucan content in mycelium-on-grain products, versus 30–40% in fruiting body extracts (McCleary & Draga, Journal of AOAC International, 2016)
35–40%
starch content typically found in mycelium-on-grain supplement powders after the grain substrate is included (McCleary & Draga, 2016)
26.3%
US reishi supplement products meeting acceptable quality standards in a 38-product analytical survey (Wu et al., Scientific Reports, 2017)
Tarsitano et al., Journal of Fungi, 2023
View as image ↗The ingredient labeled "mushroom" in many supplement capsules is not what most people picture. It is not a dried mushroom cap or a mushroom extract. It is a powder ground from mushroom mycelium, the thread-like root structure, that was grown on a grain substrate and then processed whole, grain and all, into the final product. The starch from that grain does not get removed. It ends up in the capsule. Understanding why this happens, and what it means for the active compound content of mushroom supplements, is what this article covers. For the regulatory context that explains why this practice persists, see the complete guide to FDA regulation of mushroom supplements.
Key Takeaways
- Mycelium-on-grain production is the dominant manufacturing method for US mushroom supplement companies; it produces powder containing 35–40% grain starch by weight, confirmed analytically by McCleary & Draga in 2016
- Fruiting body extracts (from the actual mushroom cap) average 30–40% beta-glucan content; mycelium-on-grain products average 5–7% beta-glucan, a 4–6x gap in active compound concentration (McCleary & Draga, 2016)
- "Total polysaccharides" on a supplement label does not mean beta-glucans: standard polysaccharide tests count grain starch (alpha-glucan) as polysaccharides, inflating the apparent active compound content
- The correct measurement is a specific enzymatic assay that distinguishes fungal (1,3)/(1,6)-beta-glucan from alpha-glucan starch; only this test accurately represents mushroom bioactive content (McCleary & Draga, 2016)
- Quality surveys confirm the downstream problem: 26.3% of US reishi products tested met acceptable quality thresholds (Wu et al., 2017) and 31.6% of 120 European products were correctly labeled (Tarsitano et al., 2023)
- The practice is largely an industry convention driven by economics, not necessarily fraudulent intent; mycelium-on-grain costs a fraction of fruiting body and the FDA has not explicitly prohibited it
How Mycelium-on-Grain Became the Default Ingredient in Most US Mushroom Supplements
The mushroom supplement industry has two main production methods, and they produce radically different raw materials.
The first method cultivates the fruiting body, the actual mushroom, through traditional growing and then dries, powders, or extracts it. This produces material with measurable concentrations of the active compounds that medicinal mushroom research studies: beta-glucans, triterpenes, and other bioactives found in the fungal tissue itself. It also requires time, substrate management, and harvesting, the same agricultural process used for edible mushrooms.
The second method grows mushroom mycelium (the root-like network of fungal threads) on grain, typically rice or oats, inside a fermentation vessel or grow bag. After a set incubation period, the grain-mycelium mixture is dried and milled. The resulting powder goes into capsules. The grain is never removed.
The economics explain the method's dominance. Mycelium cultivated on grain substrate can be produced in controlled indoor facilities, scaled rapidly, and processed in weeks rather than months. The grain substrate itself is cheap. Growing mycelium on grain requires less specialized infrastructure than cultivating, drying, and extracting fruiting bodies at scale. The cost differential between these two production routes is substantial, and US supplement manufacturing has largely built itself around the faster, cheaper option.
This is the commercial reality behind most mushroom supplement brands sold online and in US retail stores. It is not universally disclosed on labels. Many products simply list "reishi," "lion's mane," or "turkey tail" without specifying the form of the ingredient.
What Stays in the Jar After Manufacturing: 35–40% Starch
When mycelium is grown on grain and the mixture is processed whole, the resulting powder is a blend of fungal material and grain residue. The proportion of each depends on how completely the mycelium colonized the substrate and how long the fermentation ran. For products sold in the US market, the grain fraction is substantial.
McCleary and Draga validated this in a 2016 methodology paper published in the Journal of AOAC International, which established the enzymatic assay for measuring fungal beta-glucans.[1] Their measurements of commercial mycelium-on-grain products showed an average starch content of 35–40% by weight. In a 500mg capsule, that is 175–200mg of grain starch per dose.
The starch is not an added filler in the traditional supplement sense, where an excipient is blended in to improve capsule fill. It is structurally inseparable from the fermented substrate. Removing the grain would require a solvent extraction process that would fundamentally change the ingredient, add processing steps, and increase cost. Most producers using this method do not perform that extraction. The mycelium-grain mixture is the product.
The consequence for active compound concentration is directly measured. Where fruiting body material averages 30–40% beta-glucan content, the same weight of mycelium-on-grain powder averages 5–7% beta-glucan.[1] A consumer taking the same gram-for-gram dose receives roughly one-fifth to one-seventh the fungal bioactive content.
Why "Total Polysaccharides" Is Not the Same as "Beta-Glucans"
If mycelium-on-grain products contain 5–7% beta-glucan and 35–40% starch, yet many labels claim high polysaccharide content, there is an obvious question: what is the label measuring?
The answer is that most polysaccharide testing in the supplement industry does not distinguish between fungal beta-glucan polysaccharides and grain alpha-glucan polysaccharides (starch). Standard carbohydrate measurement methods count all polysaccharides. Starch is a polysaccharide. If a product is 35–40% starch by weight, a generic polysaccharide test will capture that starch and report it as polysaccharide content.
This is precisely what McCleary and Draga's 2016 work addressed.[1] They validated an enzymatic assay that specifically measures (1,3)/(1,6)-beta-D-glucan, the type of polysaccharide found in fungal cell walls and associated with the immune-modulating effects in the research literature. This assay uses a specific enzyme to digest alpha-glucan (starch) first, leaving only the fungal beta-glucan to be measured. The starch signal is removed from the measurement.
When products are tested with the generic polysaccharide method versus the specific beta-glucan assay, the results diverge dramatically. A product that reads 30% polysaccharides by generic methods might show 5–7% beta-glucan once the grain starch is accounted for and excluded.
The label term "total polysaccharides" technically discloses what is being measured: the total of all polysaccharides, including starch. But consumers reading "total polysaccharides 30%" on a supplement label reasonably interpret that as 30% mushroom bioactives. The measurement is accurate; the interpretation that follows from it is not.
Beta-glucan content, measured by the specific enzymatic assay, is what the research literature measures. It is the number that corresponds to the compound classes studied in clinical trials and mechanistic research.
Fruiting Body vs. Mycelium on Grain: The Numbers Side by Side
The measured difference between these two ingredient types, using the validated beta-glucan assay, is the following:
| Parameter | Fruiting Body Extract | Mycelium on Grain |
|---|---|---|
| Average beta-glucan content | 30–40% | 5–7% |
| Average starch (alpha-glucan) content | less than 3% | 35–40% |
| Active compound density per gram | High | Low |
| Grain residue present | No | Yes, inherent |
Source: McCleary & Draga, Journal of AOAC International, 2016[1]
The Windsor and colleagues 2025 study, a comparative analysis of commercial Chaga supplements using multiple complementary analytical techniques including NMR, HPTLC, and beta-glucan assays, confirmed that significant quality variation exists across products and that analytical chemistry reliably detects it.[4] Jeff Chilton, founder of NAMMEX (the North American Medicinal Mushroom Extracts company and originator of much of the quality standards framework for the industry), was a co-author. When the person who established the quality standards for the industry signs their name to a paper documenting the problem, the finding is difficult to dispute on credibility grounds.
The practical implication scales with the dose. A consumer buying a 500mg capsule product with 5% beta-glucan receives 25mg of fungal beta-glucan per capsule. The same product claiming 30% total polysaccharides and 35% starch content has 25mg beta-glucan and 175mg starch per capsule. A fruiting body extract at 30% beta-glucan in the same capsule delivers 150mg of beta-glucan per dose.
What Product Testing Found: 26.3% and 31.6%
The beta-glucan concentration gap does not stay theoretical. Quality surveys show its commercial consequence.
Wu and colleagues analyzed 38 commercially available Ganoderma (reishi) supplement products sold in the US market in 2017.[2] Only 26.3% of those products, roughly 10 out of 38, met acceptable thresholds for both species identity and active compound content. Nearly three-quarters of the US reishi supplement market, in the sampled window, delivered a product that either contained the wrong species or contained substantially less bioactive content than expected.
A 2023 systematic survey by Tarsitano and colleagues tested 120 mushroom supplement products commercially available in Italy across multiple species.[3] The results were similarly stark: only 31.6% of products correctly met label claims for both species identity and beta-glucan content. More than two-thirds of the market sample failed. The researchers named their paper "Let's Open Pandora's Box," a characterization that the data justifies.
These are not cherry-picked studies. They are among the few systematic analytical surveys of commercial mushroom supplement quality conducted by independent researchers using validated assays. The pattern they describe, roughly 26–32% of products meeting quality expectations, suggests that substandard quality is the norm in the market, not the exception.
The full scope of the adulteration problem across all mushroom species, including species misidentification separate from the starch issue, is covered in the companion article on how widespread mushroom supplement adulteration is. The specifics of how to test for starch at home and how to read a COA for beta-glucan vs. alpha-glucan content are in how to spot adulterated mushroom products.
Why This Practice Is Still Legal: The Regulatory Grey Zone
Mycelium-on-grain supplements can be sold legally because the regulatory framework governing dietary supplements does not require specific proof of bioactive content before a product reaches market.
The Dietary Supplement Health and Education Act (DSHEA), enacted in 1994, places the burden on manufacturers to ensure their products are safe and accurately labeled. The FDA does not pre-approve dietary supplements. It acts after the fact when evidence of a problem emerges. Manufacturers are required to follow Current Good Manufacturing Practices, which include identity and potency testing, but the agency does not independently verify those tests before products ship.
"Mushroom mycelium" is a legitimate dietary ingredient. "Mycelium-on-grain" is a production method, not a prohibited adulterant under current FDA guidance. A product that correctly labels its ingredient as "mushroom mycelium" (even if it contains grain starch) is not, under current regulatory interpretation, mislabeled in the same way that a product claiming the wrong species would be. It is meeting the letter of label compliance while potentially falling short of what a consumer intuitively expects.
The companion article on how DSHEA shapes what mushroom supplement companies can and can't say covers this regulatory structure in depth. For species-specific mislabeling, where a product claims to contain one mushroom species but DNA testing reveals another, the standards and enforcement record are different, as covered in DNA testing for mushroom supplements.
What this regulatory context means for consumers: the quality gap between products is real, analytically confirmed, and not currently being closed by enforcement alone. The label distinction between "total polysaccharides" and "beta-glucans" remains unregulated in terms of mandatory disclosure. Brands that test to the stricter standard and publish their COA data are self-differentiating against a baseline that does not require them to do so.
For a practical guide to label reading, what to ask a manufacturer, and how to interpret a COA, see how to read a mushroom supplement label.
The Bottom Line
The starch problem in mushroom supplements is primarily an economic and regulatory issue, not a fraud scandal. Mycelium-on-grain production is cheaper and faster than fruiting body cultivation, and FDA regulation does not require pre-market testing of bioactive content. The result is a market where most products by volume are manufactured using a method that delivers 5–7% beta-glucan with 35–40% grain starch, versus the 30–40% beta-glucan typical of fruiting body extracts. Laboratory surveys confirm the consequence: roughly 26–31% of products tested in the US and Europe meet acceptable quality thresholds. The analytical tools to identify high-quality products exist; the question is whether those tools are used and disclosed.
Frequently Asked Questions
Sources & References
- 1RTHM-00438·McCleary, Barry V et al. (2016). “Measurement of β-Glucan in Mushrooms and Mycelial Products..” Journal of AOAC International.Study breakdown →PubMed →↩
- 2RTHM-00499·Wu, Ding-Tao et al. (2017). “Evaluation on quality consistency of Ganoderma lucidum dietary supplements collected in the United States..” Scientific reports.Study breakdown →PubMed →↩
- 3. Source details for this reference are not yet available.
- 4RTHM-02209·Windsor, Coleton et al. (2025). “What This 2025 Chaga Supplement Authentication Study Actually Found.” International journal of molecular sciences.Study breakdown →PubMed →↩