Mulberry and the Gut Microbiome

Table of Contents

1. 1. What Kind of Paper This Is
2. 2. Leaf Versus Fruit: Two Different Materials
3. 3. Processing Changes the Material
4. 4. White Mulberry Fruit in High-Fat-Diet Mice
5. 5. The Gut-Bacteria Transfer Experiment
6. 6. Leaf Polyphenols Plus Fibre in Obese Mice
7. 7. Test-Tube Fermentation with Human Stool Samples
8. 8. The Mechanism in Plain Language
9. 9. Press Release Versus Paper, and Safety Figures
10. 10. Limits and What Remains Unknown
11. Key Research Papers
12. Connections

1. What Kind of Paper This Is

The paper is Miszczak, Kłosowska-Buryło, Pieczyńska, Bielecka and Prescha, “Mulberry, Gut Microbiota and Gut Functionality: Effects Shaped by Raw Material and Processing Methods,” Biomolecules 2026, volume 16, issue 7, article 965. It is indexed in PubMed (PMID 42509759) and is freely readable in PubMed Central under an open licence.

It is a narrative review. That matters for how its findings are read. A narrative review runs no new experiment of its own; the authors searched the literature, read other groups' studies and wrote a structured summary of them. Their stated search terms were “mulberry,” “Morus alba,” “Morus nigra,” “mulberry leaf” and “mulberry fruit,” combined with keywords for the gut topics they covered. The reference list runs to 176 papers. Unlike a systematic review, a narrative review does not pool results statistically or grade each study by a fixed protocol, so it describes the shape of a field rather than measuring an average effect.

Who wrote it

The authors work in the Department of Dietetics and Bromatology and the Department of Pharmaceutical Biology and Biotechnology at Wroclaw Medical University, with a student research group called “Nutri-Sfera.” The paper declares no conflict of interest. The corresponding author on the paper is Monika Bielecka; the press release quoted Anna Prescha, the senior author.

What kinds of studies it draws on

• Animal studies — mostly mice fed a high-fat diet, plus genetically diabetic (db/db) or chemically diabetic mice, and some studies in piglets.
• In vitro fermentation — mulberry material incubated in the laboratory with bacteria taken from human stool samples, to see what the bacteria do with it.
• No human intervention trials of the microbiome. The authors state that no well-controlled clinical trial has yet measured gut bacteria, short-chain fatty acids, gut permeability or inflammation in people given mulberry.

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2. Leaf Versus Fruit: Two Different Materials

A central point of the review is that “mulberry” is not one substance. The leaf and the fruit contain different families of compounds, and the bacteria in the gut meet different things depending on which part is eaten.

Leaves

The review describes mulberry leaves as high in three groups of compounds:

• Iminosugars, above all 1-deoxynojirimycin (DNJ). DNJ looks enough like glucose to block the gut enzymes that split starch and sugar into absorbable glucose. This site's page on blood sugar and post-meal spikes covers that effect and its human trials in detail.
• Flavonols and flavones, plant pigments of the polyphenol family.
• Polysaccharides, long sugar chains that human digestive enzymes do not break down.

Fruits

The fruits, “especially Morus nigra,” in the review's words, carry substantial amounts of anthocyanins — the red-to-purple pigments also found in blackberries and blackcurrants — together with other phenolic compounds and their own polysaccharides. White mulberry fruit, which several of the animal studies used, also contains polyphenols and polysaccharides, in different proportions.

Why the difference matters for gut bacteria

Polyphenols and polysaccharides behave differently in the gut. Much of a polyphenol dose is not absorbed in the small intestine and passes to the colon, where bacteria transform it. Polysaccharides that escape digestion become food for bacteria that can ferment them. The review's summary statement is that responses “differ across plant parts, species, and preparation approaches,” and that a leaf study and a fruit study are not interchangeable evidence.

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3. Processing Changes the Material

The review's title puts “processing methods” next to raw material, and the authors return to it throughout. The composition of what reaches the gut depends on what was done to the leaf or fruit before it was eaten or tested. The processing steps the review lists are:

• Drying of leaves or fruit, which changes the amount of heat-sensitive compounds such as anthocyanins.
• Maceration, soaking the plant material in a liquid.
• Fermentation of the leaf or fruit before use.
• Extraction, where the solvent decides what comes out: a water (aqueous) extract pulls out a different mix from a water-alcohol (hydroalcoholic) extract.
• Fractionation, splitting an extract into enriched fractions — a polyphenol fraction, a polysaccharide fraction, a DNJ-standardised fraction.

Most of the animal studies below did not feed whole mulberry leaves or fruit. They fed purified fractions or extracts. The authors point out that two studies both described as “mulberry” may have tested materials with little in common, and that many papers do not report the composition of what they tested in enough detail for a reader to compare them. They name this incomplete and inconsistent reporting as one of the main limits of the field (section 10).

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4. White Mulberry Fruit in High-Fat-Diet Mice

The study the press release highlighted is a 2022 paper by Wan and colleagues in Foods. Mice were fed a high-fat diet, a standard laboratory model of metabolic syndrome: the animals gain fat, their blood lipids and blood sugar worsen, and their gut bacteria shift.

The design

The researchers separated white mulberry (Morus alba) fruit into a polyphenol fraction and a polysaccharide fraction. Groups of high-fat-diet mice received the polyphenols alone, the polysaccharides alone, or the two in combination.

The results

• Each fraction on its own improved markers of metabolic syndrome in the mice.
• In the words of the paper's abstract, “the group treated with polyphenols and polysaccharides in combination showed better efficacy.”
• Bacteria that rose: Muribaculum and the Lachnospiraceae NK4A136 group.
• Bacteria that fell: Prevotella_2, Bacteroides, Faecalibacterium and Fusobacterium.
• Faecal metabolites: 23 metabolites in the droppings differed between groups. The Foods abstract relates these 23 to the treatments “individually and in combination.” The review describes the combination as producing “a distinct fecal metabolite signature involving 23 metabolites”; the original abstract does not attribute all 23 to the combination alone.

Reading the bacterial changes

A fall in Faecalibacterium may look surprising, because in human research that genus is often discussed as a butyrate producer associated with gut health. Mouse and human gut communities differ, and a change in a genus in a high-fat-diet mouse does not translate directly to a person. The study reports which groups moved; it does not establish that any one of them caused the metabolic improvement.

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5. The Gut-Bacteria Transfer Experiment

Finding that bacteria change alongside a metabolic improvement leaves an open question: did the bacteria help produce the improvement, or did they simply change because the animals' metabolism changed? The same research group addressed this in a follow-up published in Scientific Reports in 2025 (Wan and colleagues).

The design

• Donor mice were dosed with the combined white mulberry fruit polyphenol-plus-polysaccharide fraction.
• Their gut bacteria were collected and transferred by faecal microbiota transplant (FMT) into recipient mice.
• The recipients were “pseudo-germ-free” — their own gut bacteria had first been depleted, typically with antibiotics — and were on a high-fat diet.
• The recipients themselves did not receive the mulberry fraction; they received only the bacteria.

The results

The recipient mice showed improved dyslipidaemia (abnormal blood fats), less organ injury and less injury to the proximal colon, and activation of a signalling pathway called PPARα/PGC-1α. PPARα is a receptor that switches on fat-burning genes, mainly in the liver; PGC-1α is a regulator of mitochondrial activity and energy use.

What it does and does not show

The review's reading is that “at least part of the biological activity of the fraction was microbiota-mediated.” That is the strongest form of evidence in this field so far, because it separates the bacteria from the plant compounds. Its limits are also clear: it is one research group, in mice, using a purified fraction rather than the whole fruit, and the full text of this paper was not read for this page, so details of group sizes and doses are not reported here.

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6. Leaf Polyphenols Plus Fibre in Obese Mice

A similar pattern — two components working better together than apart — appeared in leaf research. Two papers from one group (Li and colleagues, Nutrients 2019; Liao and colleagues, Journal of Food Science 2021) studied mulberry leaf polyphenols and mulberry leaf fibre in obese mice.

The design

The researchers compared several leaf preparations, including whole mulberry leaf powder and a combination of leaf polyphenols with leaf fibre at a ratio of 1 to 4 by weight.

The results

• The polyphenol-plus-fibre combination (1:4 w/w) produced the greatest weight-loss effect of the preparations tested.
• It also outperformed whole leaf powder, even though whole leaf contains both components.
• The mice given the combination had more Lactobacillus johnsonii in the gut.
• The ratio of two major bacterial groups, Bacillota to Bacteroidota (formerly called Firmicutes and Bacteroidetes), was lower.

Why the ratio is mentioned

The Bacillota-to-Bacteroidota ratio was proposed in early microbiome research as a marker associated with obesity in mice. Later work found the association inconsistent, especially in humans, so a change in the ratio is a description of the mouse gut community rather than proof of a health effect. The papers report the change; the weight result is the outcome measured directly.

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7. Test-Tube Fermentation with Human Stool Samples

The closest the field has come to human gut bacteria is in vitro fermentation: stool samples from human volunteers are used as a starter culture, mulberry material is added, and the mixture is incubated in the laboratory under conditions that mimic the colon. These studies show what human gut bacteria can do with mulberry material. They do not show what happens when a person eats it, because the material has not passed through the stomach and small intestine, and the person's immune system, gut lining and diet are absent.

Black mulberry fruit polysaccharides (Ai and colleagues, 2022)

• Polysaccharides were extracted from black mulberry fruit by several methods, including hot water and enzyme-assisted extraction.
• All of the extracts were fermented by the human faecal bacteria, and all raised short-chain fatty acids.
• The water-extracted fraction and the fraction extracted with the enzyme pectin lyase showed the highest fermentability and prebiotic potential.
• Bacteroidota and Bacillota increased; Pseudomonadota and Fusobacteriota decreased.

The result supports the review's processing theme directly: the same fruit, extracted differently, gave polysaccharides that bacteria fermented to different degrees.

Mulberry fruit polysaccharides (Chen and colleagues, 2016)

In an earlier study tabulated in the review, mulberry fruit polysaccharides incubated with human faecal inocula were about 45 percent consumed within 48 hours. The pH of the culture fell, as it does when bacteria ferment carbohydrate into acids, and total short-chain fatty acids rose.

The pattern across the field

Summarising the animal and laboratory work as a whole, the review's abstract states that preclinical studies “frequently” report enrichment of Bifidobacterium, Lactobacillus and Akkermansia, normalisation of bacterial patterns associated with dysbiosis, and higher short-chain fatty acids — acetate, propionate and butyrate. These changes were “sometimes observed alongside” better glucose regulation, lipid profile, adiposity or inflammatory markers. The wording is careful: frequently, not always; sometimes alongside, not caused by.

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8. The Mechanism in Plain Language

The review proposes a chain of events, drawn from the animal and laboratory studies. Each link is supported in those models; the whole chain has not been tested in people.

Step 1: Material reaches the colon

Mulberry polysaccharides and fibre are not digested by human enzymes, and many mulberry polyphenols are poorly absorbed in the small intestine. Both pass on to the large intestine. Leaves add a further route: by slowing the enzymes that digest starch and sugar, DNJ can leave some carbohydrate undigested, and undigested carbohydrate also travels on to the colon. The blood sugar page describes a human study in which a tea extract that included mulberry caused part of a carbohydrate load to be malabsorbed.

Step 2: Bacteria ferment it

Colon bacteria that can break down these polysaccharides grow on them, and the bacteria transform polyphenols into smaller compounds. This is what “prebiotic potential” means in the fermentation studies: the material feeds particular bacteria.

Step 3: Short-chain fatty acids are made

Fermentation produces short-chain fatty acids, mainly acetate, propionate and butyrate. Butyrate is the main fuel of the cells lining the colon, and these acids also act as signals that reach the liver and other tissues. This site's gut barrier and microbiome animation shows the process step by step.

Step 4: Effects beyond the gut, in animals

In the mouse studies, the shifted bacterial community went together with better blood fats, less fat gain and lower inflammatory markers, and in the transfer experiment the bacteria alone were enough to produce part of the effect, with the PPARα/PGC-1α fat-burning pathway switched on in the recipients.

The synergy question

Two studies, one on fruit and one on leaf, found a combination of polyphenols with polysaccharide or fibre doing better than either part alone. The review does not settle why. One possibility consistent with the findings is that the fibre feeds bacteria that also process the polyphenols, but no study described in the review proves a specific explanation.

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9. Press Release Versus Paper, and Safety Figures

The press release, issued through ScienceDaily on 30 September 2026 with Wroclaw Medical University as the source, is largely faithful to the review. Checked claim by claim against the paper:

Supported by the paper

• The combined polyphenol-plus-polysaccharide fraction from white mulberry fruit outperformed either fraction alone in high-fat-diet mice.
• The faecal transplant experiment, in which bacteria from treated mice improved metabolic markers in recipient mice.
• Mulberry leaves contain DNJ; black mulberry fruit is high in anthocyanins.
• Processing changes composition, and results are inconsistent across preparations.

Where the wording differs

• The enzyme name. The press release refers to “pectate lyase.” The paper names pectin lyase, which is a different enzyme. This page follows the paper.
• Human studies. The press release says researchers have not yet conducted human studies directly examining mulberry and the gut microbiota. The paper's statement is narrower: there are no well-controlled human clinical trials. It does describe laboratory fermentation studies using human stool samples — human bacteria, but not people eating mulberry. The accurate summary is that no controlled trial in people has measured it.
• The headline. “May reshape gut bacteria and influence metabolism” rests entirely on animal and laboratory evidence. Every finding carries the qualifier “in mice” or “in laboratory studies.”
• The 23 metabolites. As noted in section 4, the original study relates the 23 differing metabolites to the treatments individually and in combination, not to the combination alone.

What neither document says

Neither the review nor the press release gives a human dose for any gut effect, and neither names any product or brand.

Safety figures the review reports

The review summarises safety data from other studies (the underlying papers were not separately checked for this page):

• Aqueous extracts of Morus alba leaf had a median lethal dose (LD₅₀) above 15 g per kilogram of body weight in animals — a very low acute toxicity.
• A DNJ-standardised extract had a no-observed-adverse-effect level (NOAEL) of 4 g per kilogram per day in a 28-day animal study.
• Human studies giving 18–36 mg of DNJ per day “generally reported only mild gastrointestinal symptoms, including bloating, flatulence, and abdominal discomfort.” Those symptoms fit the mechanism in section 8: carbohydrate that is not digested is fermented by colon bacteria, which produces gas.

The site's page on timing and side effects covers the human tolerability research and reported drug interactions in more detail.

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10. Limits and What Remains Unknown

The authors are direct about the state of the evidence. Their own statements:

• “the most important limitation of the current evidence base is the absence of well-controlled human clinical trials evaluating gut microbiota, SCFA production, intestinal permeability, and inflammatory outcomes following mulberry supplementation.”
• “most of the mechanistic relationships discussed in this review remain supported primarily by animal models and in vitro fermentation systems.”
• The evidence is limited “by incomplete or inconsistent reporting of extract composition, processing conditions, and standardization procedures.”
• Direct comparisons of white mulberry (M. alba) with black mulberry (M. nigra) are lacking.

Open questions that follow

• Do the mouse changes happen in people? Mouse and human gut communities differ in which bacteria dominate, and high-fat-diet mice are a model, not a patient group.
• Whole food or fraction? Most studies used purified fractions. Whether eating whole mulberry fruit or drinking leaf tea gives the same effect is untested; in the leaf study, the whole leaf powder did less than the combined fraction.
• What amount? No study described in the review translates an animal dose into a human gut effect.
• Which bacteria matter? The taxa that rise or fall differ between studies, and none has been shown to carry the effect on its own.
• How long do changes last? The studies are short, and whether a shift persists after mulberry is stopped is not reported.
• Fruit research on this site. The strongest single finding concerns the fruit, while the research on this site so far centres on the leaf.

Where this fits

For the leaf's best-studied human effect — flattening the blood-sugar rise after a carbohydrate meal — there are randomised human trials, covered on the blood sugar page. For the gut microbiome, the evidence is at an earlier stage: a consistent pattern in animals and laboratory fermentation, one transfer experiment suggesting the bacteria carry part of the effect, and no controlled human trial yet.

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Key Research Papers

1. Miszczak MM, Kłosowska-Buryło K, Pieczyńska JM, Bielecka M, Prescha A (2026). Mulberry, Gut Microbiota and Gut Functionality: Effects Shaped by Raw Material and Processing Methods. Biomolecules 16(7):965 — PubMed PMID: 42509759
2. Wan M, Li Q, Lei Q, Zhou D, Wang S (2022). Polyphenols and Polysaccharides from Morus alba L. Fruit Attenuate High-Fat Diet-Induced Metabolic Syndrome Modifying the Gut Microbiota and Metabolite Profile. Foods 11(12):1818 — PubMed PMID: 35742014
3. Wan M, Li Q, Xiao Y, Zhou D, Lei Q, Wang S (2025). Gut microbiota from Mori fructus (Morus alba L.) polyphenols and polysaccharides-dosed mice activates the PPARα/PGC-1α signaling pathway to mitigate HFD-induced metabolic syndrome in mice. Scientific Reports 15(1):28137 — PubMed PMID: 40750814
4. Li Q, Liu F, Liu J, Liao S, Zou Y (2019). Mulberry Leaf Polyphenols and Fiber Induce Synergistic Antiobesity and Display a Modulation Effect on Gut Microbiota and Metabolites. Nutrients 11(5):1017 — PubMed PMID: 31064150
5. Liao S, Long X, Zou Y, Liu F, Li Q (2021). Mulberry leaf phenolics and fiber exert anti-obesity through the gut microbiota-host metabolism pathway. Journal of Food Science 86(4):1432–1447 — PubMed PMID: 33761137
6. Ai J, Yang Z, Liu J, Schols HA, Battino M, Bao B, Tian L, Bai W (2022). Structural Characterization and In Vitro Fermentation Characteristics of Enzymatically Extracted Black Mulberry Polysaccharides. Journal of Agricultural and Food Chemistry 70(12):3654–3665 — PubMed PMID: 35311256
7. Chen C, Huang Q, Fu X, Liu RH (2016). In vitro fermentation of mulberry fruit polysaccharides by human fecal inocula and impact on microbiota. Food & Function 7(11):4637–4643 — PubMed PMID: 27748781

PubMed Topic Searches

1. PubMed: Mulberry and gut microbiota
2. PubMed: White mulberry fruit polysaccharides and microbiota
3. PubMed: Black mulberry anthocyanins
4. PubMed: Mulberry leaf and short-chain fatty acids
5. PubMed: DNJ and gut microbiota
6. PubMed: Mulberry in vitro fermentation with human faecal samples

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Connections

• All Herbs
• White Mulberry Leaf Benefits
• White Mulberry Leaf (Morus alba)
• Blood Sugar and Post-Meal Spikes
• Cholesterol and Cardiovascular
• Timing and Side Effects
• News, October 11, 2026
• The Gut Microbiome
• Gut Barrier and Microbiome (animation)
• Anthocyanins
• Gut-Brain Axis
• Metabolic Syndrome
• Berberine and the Gut Microbiome
• Threonine, Gut Mucin and Barrier

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