Mushrooms for Prediabetes: Can Early Intervention Prevent Type 2?

Mushrooms, Prediabetes & Metabolic Syndrome

2 outcomes improved in prediabetes RCT

A 2024 randomized controlled trial found that a Tremella fuciformis mushroom beverage improved both HbA1c and waist circumference in overweight/obese prediabetic adults compared to placebo, among the first RCTs to test a specific mushroom beverage in prediabetes and measure both a glycemic and an abdominal-fat outcome.

Gitsomboon et al., 2024

HbA1c improved

3-month blood sugar average reduced in Tremella prediabetes RCT, 2024

Waist circumference reduced

visceral fat marker improved in the same 2024 trial

GLP-1 raised 17%

oyster mushroom powder raised the GLP-1 response in a 2022 IGT crossover RCT, the hormone targeted by semaglutide

Gitsomboon et al., 2024

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In 2024, researchers published a randomized controlled trial testing a Tremella fuciformis mushroom beverage in overweight/obese adults with prediabetes. Compared to placebo, the Tremella group showed significant improvements in HbA1c, which is the three-month blood sugar average that doctors use to diagnose and track prediabetes, as well as reduced waist circumference.^[1] That combination of outcomes (glycemic control and abdominal fat) is precisely what matters for preventing the progression from prediabetes to type 2 diabetes.

No patient-facing resource covers this study. Most mushroom and diabetes content relies on older animal studies or generic mechanistic reviews. The 2024 Tremella trial and a 2022 oyster mushroom crossover trial showing an increased GLP-1 response (with a 2025 follow-up analysis of the same trial) represent the most current human clinical data available, and they have not yet reached the mainstream.

For the broader picture of how mushrooms affect blood sugar across multiple species, see our research guide to mushrooms and type 2 diabetes.

Why Prediabetes Is the Window That Matters Most for Dietary Intervention

Prediabetes is defined by blood glucose levels that are elevated but not yet in the diabetic range: an HbA1c of 5.7-6.4%, or a fasting blood glucose of 100-125 mg/dL. Approximately 38% of US adults meet this definition, and without intervention, roughly 25% will progress to type 2 diabetes within 3-5 years.

The prediabetes window matters because the biology of progression is still reversible. Beta cells in the pancreas, which produce insulin, are still functioning. Insulin resistance can still be reduced through diet, exercise, and weight management. Once type 2 diabetes is established, the intervention calculus changes: the damage to beta cell function may be partly permanent, and the primary goal becomes management rather than reversal.

This is why early dietary interventions are worth studying carefully. A food that modestly improves postprandial glucose, supports insulin sensitivity, or reduces visceral fat in the prediabetes window has a different clinical value than the same food given to someone with established type 2 diabetes and compromised pancreatic function.

A 2023 systematic review examining mushrooms and cardiometabolic health noted that the human evidence base is still maturing, with the most consistent benefits seen for triglyceride reduction and inflammatory marker improvement rather than HbA1c specifically.^[5] The 2024 and 2025 studies are among the first to test specific mushroom interventions specifically in the prediabetes population.

The 2024 Tremella RCT: Two Prediabetes Outcomes Improved in a Single Trial

Tremella fuciformis, commonly called snow fungus or white jelly mushroom, is widely used in Chinese culinary and traditional medicine contexts. Compared to maitake, reishi, or oyster mushroom, it receives far less attention in Western functional food research. The 2024 trial by Gitsomboon and colleagues is therefore notable on two counts: it tested a less-studied species, and it did so specifically in overweight/obese prediabetic adults rather than in already-diabetic or generally healthy populations.^[1]

The double-blind trial randomized 56 participants to a once-daily Tremella fuciformis beverage or placebo for 12 weeks. Both HbA1c (6.03% to 5.96%, a small but statistically significant change) and waist circumference (95.2 cm to 93.5 cm) improved significantly in the Tremella group, with no adverse events reported. The dual outcome is clinically meaningful: HbA1c improvement indicates better average glucose management over the preceding three months, while waist circumference reduction indicates a reduction in visceral (abdominal) fat, which is both a criterion for metabolic syndrome and a driver of insulin resistance. The effect sizes were modest (Cohen's d around 0.4), consistent with a dietary rather than pharmacological intervention.

Why might Tremella specifically improve these outcomes? The proposed mechanism goes through beta-glucan content. Tremella polysaccharides are structurally distinct from the beta-glucans in oyster mushroom or oat fiber, but they share the general property of resisting human digestive enzymes and reaching the colon for fermentation. The fermentation products, short-chain fatty acids, activate intestinal hormone pathways and modulate gut bacteria in ways that affect glucose metabolism and adipogenesis.

The Tremella trial represents the most directly relevant human evidence currently available for mushrooms in prediabetes. It is small-scale and recent, and replication in larger trials would strengthen its conclusions. But for a population searching for evidence-based dietary strategies, it is a meaningful data point that predates this article's publication and deserves to be cited.

For research on how mushrooms affect waist circumference and visceral fat more broadly, see Mushrooms and Visceral Fat: Research on Abdominal Adiposity Reduction.

Oyster Mushroom in Impaired Glucose Tolerance: What the Postprandial Data Actually Shows

Impaired glucose tolerance is a specific subset of prediabetes defined by elevated blood glucose specifically two hours after eating, even when fasting glucose is normal. It is often the earliest detectable signal that glucose metabolism is starting to fail.

A 2022 double-blind randomized controlled crossover trial by Dicks and colleagues tested oyster mushroom powder in 22 adults with impaired glucose tolerance.^[2] Each participant consumed a standardized meal with 20 grams of dried Pleurotus ostreatus powder containing 8.1 grams of beta-glucan, and, on a separate occasion, the same meal without mushroom.

The result is more nuanced than a simple blood-sugar-lowering story, and the details matter. Postprandial glucose (the trial's primary outcome), insulin, and triglycerides did not differ significantly between the mushroom and control meals. What did change was hormonal and metabolic: the GLP-1 response was 17% higher, non-esterified free fatty acids (NEFAs) were 14% lower, and rated hunger was 22% lower after the mushroom meal. In other words, a single fortified meal did not blunt the glucose spike itself, but it shifted the gut-hormone and fat-metabolism signals that regulate glucose control and appetite over time.

This is an acute effect measured after a single meal, not a measure of what happens to HbA1c over months of regular consumption. The authors themselves framed it cautiously: if the effect is preserved long term, it could help reduce the risk of progression to overweight and type 2 diabetes in people with impaired glucose tolerance. The specific population matters, because these are exactly the people in whom that gut-hormone signaling is beginning to falter.

For how this and similar data translate to HbA1c over time, see The Mushroom Diet and HbA1c: Can Regular Consumption Improve Long-Term Blood Sugar?.

The GLP-1 Angle: Why Oyster Mushroom Beta-Glucan May Work Through the Same Pathway as Semaglutide

GLP-1 (glucagon-like peptide-1) is a gut hormone that signals the pancreas to produce insulin after eating, slows stomach emptying to reduce post-meal glucose spikes, and signals the brain that food has been consumed. Drugs like semaglutide (Ozempic, Wegovy) work by binding GLP-1 receptors directly and continuously, which is why they improve both blood glucose and body weight simultaneously.

The GLP-1 increase in that 2022 trial is the finding most relevant to the semaglutide comparison. In 2025, Klümpen and colleagues published a secondary analysis of the same crossover study to understand why the GLP-1 response varied so much between participants.^[3] They found that the size of the meal-induced GLP-1 response depended on each person's baseline gut microbiota: the boost was larger in participants whose microbiome was more specialized in fermenting fiber into short-chain fatty acids, and specific bacterial groups (such as Eubacterium ventriosum) were linked to a stronger response.

This matters for prediabetes specifically because GLP-1 is one of the hormones that progressively fails as the body moves from prediabetes toward type 2 diabetes. The beta-glucan in oyster mushroom feeds gut bacteria that ferment it into short-chain fatty acids, which then stimulate intestinal L-cells to release GLP-1. This is the same biological pathway that semaglutide engages, approached from a dietary rather than pharmacological direction.

Mushrooms do not bind GLP-1 receptors the way semaglutide does, and they do not produce the magnitude of sustained GLP-1 activation that a drug produces. But for someone with prediabetes managing their condition through diet and lifestyle, a meal-timed GLP-1 boost represents a real, evidence-grounded metabolic signal, one whose size appears to depend partly on the gut microbiome you bring to the meal.

For the full treatment of the oyster mushroom GLP-1 evidence and how gut microbiome composition predicts the size of the response, see Mushrooms and GLP-1: Can Fungi Mimic the Ozempic Effect?.

What the Systematic Evidence Shows (and What It Does Not)

Two data points make the prediabetes case for mushrooms: a 2024 prospective cohort study of 16,666 Korean adults finding higher dietary mushroom intake was inversely associated with type 2 diabetes risk at the population level,^[4] and the 2023 Uffelman systematic review synthesizing what the accumulated evidence actually shows.

The Uffelman review conclusion is worth stating precisely. Across the 22 human studies that met inclusion criteria, limited experimental evidence suggested mushroom consumption improves triglycerides and hs-CRP (a marker of systemic inflammation), but not measures of glucose control (fasting glucose and HbA1c), other lipids, or blood pressure.^[5]

This is an honest picture. Triglyceride improvement and reduced inflammation are meaningful cardiometabolic benefits, and both are relevant to prediabetes risk. But HbA1c improvement from general mushroom consumption, as measured in older studies, was not strongly demonstrated. The 2024 Tremella trial represents newer, more targeted evidence that may shift this picture, but the systematic evidence base as a whole remains in development.

A 2016 retrospective study by Calvo and colleagues analyzed 37 adults with metabolic syndrome who had consumed 100 grams of white button mushrooms daily for 16 weeks; they showed increased antioxidant capacity (ORAC), higher adiponectin (an anti-inflammatory hormone associated with improved insulin sensitivity), and decreased oxidative stress markers, without measurable changes in glucose metabolism or insulin resistance.^[6] This pattern appears in several mushroom studies: benefits to inflammatory and oxidative markers precede or occur without directly measurable glucose changes in the study timeframe.

For a broader epidemiological picture of mushroom consumption and metabolic syndrome risk, see Mushroom Consumption and Metabolic Syndrome Risk: Epidemiological Evidence. For the evidence specifically on reishi and metabolic markers, see Reishi for Metabolic Syndrome: Addressing Inflammation, Lipids, and Glucose Together.

Which Mushrooms Show the Most Promise: The Evidence Hierarchy

For the prediabetes-specific question, three species have the strongest human evidence.

Human Evidence, At a Glance

What Each Study Actually Moved — and What It Did Not

Study

What improved

Caveat / unchanged

Tremella beverage^[1]

Gitsomboon 2024 · RCT, n=56, 12 wk

HbA1c and waist circumference both improved (small, significant)

Effect sizes modest (Cohen’s d ≈ 0.4)

Oyster meal^[2]

Dicks 2022 · IGT crossover, n=22

GLP-1 +17%, free fatty acids −14%, hunger −22%

Glucose, insulin and triglycerides unchanged

Oyster + microbiome^[3]

Klümpen 2025 · re-analysis of the 2022 trial

GLP-1 response larger with fiber-fermenting gut bacteria

Explains who responds, not a new outcome

Dietary intake^[4]

Kim 2024 · cohort, n=16,666

Higher mushroom intake linked to lower T2D risk

Association only — not a controlled trial

The strongest signal is hormonal and anthropometric, not a direct drop in the post-meal glucose spike. That distinction is why mushrooms read as a supporting dietary strategy rather than a glucose-lowering treatment.

Sources: Gitsomboon et al. (2024) [ref 1]; Dicks et al. (2022) [ref 2]; Klümpen et al. (2025) [ref 3]; Kim et al. (2024) [ref 4].

Tremella fuciformis: The 2024 RCT (Gitsomboon et al.) is the only human trial to test a specific mushroom intervention in prediabetes patients and measure both HbA1c and waist circumference as outcomes. Both improved significantly versus placebo in overweight/obese prediabetic adults.^[1] This is a single small trial and should be interpreted accordingly, but the specificity of the population and the dual outcomes make it the most directly relevant data currently available.

Oyster mushroom (Pleurotus ostreatus): A 2022 crossover trial (Dicks) showed that a single fortified meal raised the GLP-1 response and lowered free fatty acids and hunger in adults with impaired glucose tolerance, without changing postprandial glucose or insulin,^[2] and a 2025 secondary analysis (Klümpen) showed that the size of the GLP-1 response depends on baseline gut microbiota.^[3] The dose tested was 20 grams of dried oyster mushroom powder per meal, providing approximately 8.1 grams of beta-glucan.

White button mushroom (Agaricus bisporus): The Calvo 2016 retrospective study analyzed 100 grams per day for 16 weeks in metabolic syndrome adults and found improved antioxidant and anti-inflammatory markers.^[6] These markers precede or accompany glucose improvement in the metabolic syndrome pathology. White button mushroom is the most accessible and lowest-cost option among the three.

For maitake, which has extensive animal evidence for insulin sensitivity and the Georgetown University clinical research program on glucose tolerance, see Maitake and Glucose Tolerance: The Georgetown University Clinical Research.

The honest frame: no mushroom species has sufficient large-scale, long-term human trial evidence to be characterized as a prediabetes intervention in the same category as lifestyle programs like the Diabetes Prevention Program. The evidence supports mushrooms as an evidence-based dietary addition that touches several prediabetes-relevant pathways (GLP-1 signaling, free fatty acids, inflammation, and, for Tremella, HbA1c and visceral fat) but not as a standalone treatment.

This article is educational and is not medical advice. Prediabetes should be managed with a clinician, and anyone taking glucose-lowering medication should talk to their doctor before making significant dietary changes, since improved metabolic signaling can affect medication needs.

The Bottom Line

The most direct human evidence for mushrooms in prediabetes comes from a 2024 Tremella fuciformis RCT that improved both HbA1c and waist circumference in overweight/obese prediabetic adults, and a 2022 oyster mushroom crossover trial (with a 2025 microbiota follow-up analysis) showing a higher GLP-1 response and reduced free fatty acids and hunger in adults with impaired glucose tolerance, though postprandial glucose itself was unchanged. A 2023 systematic review found limited benefits for triglycerides and inflammatory markers but no clear evidence for HbA1c from general mushroom consumption. The pattern across studies supports mushrooms as a meaningful dietary addition for prediabetes risk management, with the strongest human evidence for Tremella, oyster mushroom, and white button mushroom at meaningful serving sizes.

Frequently Asked Questions

Can mushrooms prevent type 2 diabetes?

No mushroom species has been shown to prevent type 2 diabetes in large-scale clinical trials. A 2024 prospective cohort study found an association between dietary mushroom intake and lower type 2 diabetes risk, and a 2024 Tremella RCT improved HbA1c in prediabetes patients. The evidence supports mushrooms as an evidence-based dietary component of prediabetes risk reduction, not as a treatment that replaces lifestyle interventions or medical management.

Do mushrooms help with prediabetes?

The most relevant human evidence includes a 2024 RCT in which Tremella fuciformis improved both HbA1c and waist circumference in overweight/obese prediabetic adults, and a 2022 crossover RCT in which oyster mushroom powder raised the GLP-1 response and lowered free fatty acids and hunger in adults with impaired glucose tolerance, though postprandial glucose and insulin themselves did not change. A 2025 secondary analysis of that same oyster mushroom trial found the size of the GLP-1 response depends on a person's gut microbiota. The evidence is promising but early-stage; most trials are small and short-term.

What mushrooms lower blood sugar in prediabetes?

Based on human trials, the species with the most direct prediabetes evidence are Tremella fuciformis (2024 RCT showing HbA1c improvement in overweight/obese prediabetic adults) and oyster mushroom (Pleurotus ostreatus; a 2022 RCT raised the GLP-1 hormone response in impaired glucose tolerance, though it did not lower the acute post-meal glucose spike itself). White button mushroom (Agaricus bisporus) showed improved anti-inflammatory and antioxidant markers in a metabolic syndrome cohort. Maitake has clinical research on glucose tolerance at Georgetown University but is less studied specifically in the prediabetes population.

How can I reverse prediabetes naturally?

The most evidence-backed approaches to reversing prediabetes involve sustained weight loss (5-10% of body weight), aerobic exercise, and reduced refined carbohydrate intake; these come from the Diabetes Prevention Program and similar large trials. Within a dietary strategy, adding mushrooms shows some evidence of benefit across several prediabetes-relevant pathways: GLP-1 stimulation and reduced free fatty acids (oyster mushroom in IGT patients, 2022), inflammation and antioxidant markers (white button mushroom), and HbA1c and waist circumference (Tremella 2024). Mushrooms appear most useful as one dietary component within a broader strategy rather than a single intervention, and dietary changes should be coordinated with your clinician.

What foods help with prediabetes blood sugar?

Foods that reduce postprandial glucose spikes and improve insulin sensitivity are most relevant to prediabetes management. High-fiber foods including legumes, whole grains, vegetables, and mushrooms slow carbohydrate absorption. Mushrooms specifically provide beta-glucan fibers that ferment into short-chain fatty acids, which stimulate GLP-1 release and modulate glucose metabolism. Among mushrooms, oyster mushroom and Tremella have the most direct human trial evidence in prediabetes populations. General recommendations for prediabetes consistently include increased fiber from whole foods, reduced ultra-processed carbohydrates, and weight management.

Sources & References

1. 1RTHM-01892·Gitsomboon, Sawika et al. (2024). “Tremella fuciformis beverage improves glycated hemoglobin A1c and waist circumference in overweight/obese prediabetic subjects: a randomized controlled trial..” BMC nutrition.Study breakdown →PubMed →↩
2. 2RTHM-00753·Dicks, Lisa et al. (2022). “Fortifying a meal with oyster mushroom powder beneficially affects postprandial glucagon-like peptide-1, non-esterified free fatty acids and hunger sensation in adults with impaired glucose tolerance: a double-blind randomized controlled crossover trial..” European journal of nutrition.Study breakdown →PubMed →↩
3. 3RTHM-02111·Klümpen, Linda et al. (2025). “GLP-1 Responses to a Single Meal Fortified With Oyster Mushroom Powder in Adults With Impaired Glucose Tolerance Depend on the Gut Microbiota Composition Before the Meal..” Molecular nutrition & food research.Study breakdown →PubMed →↩
4. 4RTHM-01918·Kim, Yu-Mi et al. (2024). “A prospective association between dietary mushroom intake and the risk of type 2 diabetes: the Korean Genome and Epidemiology Study-Cardiovascular Disease Association Study..” Epidemiology and health.Study breakdown →PubMed →↩
5. 5RTHM-01810·Uffelman, Cassi N et al. (2023). “An Assessment of Mushroom Consumption on Cardiometabolic Disease Risk Factors and Morbidities in Humans: A Systematic Review..” Nutrients.Study breakdown →PubMed →↩
6. 6RTHM-00767·Calvo, Mona S et al. (2016). “A Retrospective Study in Adults with Metabolic Syndrome: Diabetic Risk Factor Response to Daily Consumption of Agaricus bisporus (White Button Mushrooms)..” Plant foods for human nutrition (Dordrecht.Study breakdown →PubMed →↩