Wroclaw Medical University’s dietetics group went through the mulberry literature and came away with a split verdict: preparations of the tree enriched Bifidobacterium, Lactobacillus and Akkermansia in animal studies, but what a given preparation did depended on whether it came from leaf or fruit, from white or black mulberry, and how it was dried or extracted. The review, led by Professor Anna Prescha with graduate students Marta Miszczak and Karolina Kłosowska-Buryło, appeared in the journal Biomolecules on June 30, 2026.
No human has been given these preparations in a trial that the review could count. Every microbiota result below comes from rodents or laboratory work.
Leaves, white fruit and black fruit
The Biomolecules review, titled “Mulberry, Gut Microbiota and Gut Functionality: Effects Shaped by Raw Material and Processing Methods,” opens with the chemistry. Mulberry leaves are rich in iminosugars, notably 1-deoxynojirimycin, plus flavonols, flavones and polysaccharides. The fruit, especially that of black mulberry, Morus nigra, carries substantial anthocyanins alongside other phenolic compounds and polysaccharides.
The evidence is lopsided toward leaves. White mulberry, Morus alba, leaf powder and water extracts shifted gut communities in diabetic rodent models, raising Akkermansia and Bifidobacterium and altering the ratio of Bacillota to Bacteroidota. For black mulberry the authors write that direct evidence in microbiota studies “remains very limited,” and that no one has yet compared the two species head to head on microbiota, intestinal integrity, short-chain fatty acid production or inflammation.
The leaf compound 1-deoxynojirimycin has its own track record outside the gut. A 2025 comprehensive review in Molecules by Tricase and colleagues describes it as a potent inhibitor of alpha-glucosidase, the intestinal enzyme that digests carbohydrates, which blunts the rise in blood glucose after a meal, and notes that Morus alba leaves contain high amounts of it. Because the same leaves also deliver polysaccharides that feed gut bacteria, a leaf preparation can act through more than one route at once.
That gap is why the plant-part dependence is a finding about the literature as much as about the plant. The comparison that would settle which part works best has not been run.
Drying, extraction and fermentation
Preparation changes what ends up in the extract. According to the review, freeze-drying generally holds on to anthocyanins and antioxidants better than hot-air drying, drying at 60 degrees Celsius or below preserves polyphenols, and temperatures of 70 degrees or above degrade them. Sixty-five percent acetone gave the highest total phenolic yield, 60 percent ethanol suited anthocyanins, and hot water suited polysaccharides.
The polysaccharides themselves vary enormously. Mulberry leaf polysaccharides are mostly acidic heteropolysaccharides built from mannose, rhamnose, arabinose, galactose, glucose and uronic acids, and their molecular weights run from a few kilodaltons to more than 2,700 depending on how they are extracted and purified. Fermentation can lower vitamin C and sugar and produce new metabolites, though the review reports limited microbiota data on fermented material.
One preclinical pattern stood out to the Wroclaw team. In high-fat-diet animal models, a combined preparation of polyphenols and polysaccharides from white mulberry fruit changed the microbiota more than either fraction alone. Prescha put the lesson this way in the university’s release: “What matters is not only the presence of an individual compound, but also the complex composition of the preparation, the proportions of its compounds, and their interactions.”
Short-chain fatty acids, and where the evidence stops
Alongside the bacterial shifts, the reviewed studies document higher production of the short-chain fatty acids acetate, propionate and butyrate, and some linked those microbial changes to better glucose and lipid measures. A record of the paper lists the same benefits from preclinical work: growth of the three bacterial groups, more short-chain fatty acids, and improvements in glucose regulation and inflammatory markers.
The authors are direct about the limits. They state that interpretation is restricted by “the predominance of non-human studies and by incomplete or inconsistent reporting of extract composition, processing conditions, and standardization procedures,” which makes studies hard to compare. Prescha’s team asks for human intervention trials using chemically characterized, standardized preparations before any translation to metabolic health. The project itself began when two graduate students, Miszczak in dietetics and Kłosowska-Buryło in pharmacy, proposed it through the university’s Nutri-Sfera Student Research Group, and Wroclaw Medical University reported on the review on August 18, 2026, seven weeks after the paper appeared.
Gut bacteria also sit on both sides of the polyphenol question. A 2021 review in Antioxidants notes that about 90 to 95 percent of polyphenol intake goes unabsorbed and is transformed by colonic bacteria, so the microbial community shapes which metabolites a person actually gets from a fruit or leaf. In the mulberry literature, the unanswered item is a trial in which people eat a defined, standardized preparation and the same microbiota measures are taken.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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