The mulberry tree has been consumed as food and used in traditional medicine for centuries. Now, researchers are examining whether plant compounds can alter the gut microbiota and, in turn, affect metabolism. A review involving scientists from the Medical University of Wroclaw suggests that results may largely depend on the type of mulberry, what part of the plant is used, and how it is processed.
“The gut microbiota not only contributes to the functioning of the gastrointestinal tract, but can also influence the metabolism of the entire body. Mulberry is particularly interesting in this regard because it contains numerous bioactive compounds, including polyphenols and polysaccharides, which can interact with intestinal microorganisms,” explains Anna Prescha, PhD, DSc, professor at the Medical University of Wroclaw, Department of Dietetics and Food Science.
Different blackberries contain different compounds
To date, research has focused primarily on the white mulberry (morus alba), although the black mulberry (black morus), especially its fruit, has also given notable results.
Mulberry leaves contain several biologically active substances, including 1-deoxynojirimycin (DNJ), which is known to affect carbohydrate metabolism, along with polyphenols and polysaccharides. Meanwhile, black mulberry fruit contains high levels of anthocyanins and other phenolic compounds, as well as polysaccharides.
The way the plant material is processed can also make a big difference. Drying, fermentation, and extraction methods can change both the quantity and relative proportions of bioactive compounds. As a result, two preparations made from the same plant material can differ considerably in composition and biological effects.
Mulberry can alter intestinal bacteria
The review found that preparations made from both mulberry leaves and fruits can affect the composition and activity of the intestinal microbiota. Some studies reported changes in beneficial bacteria along with increased production of short-chain fatty acids such as acetate, propionate, and butyrate.
These compounds are produced when gut microbes ferment dietary material and are important for normal intestinal function. In some experiments, changes in the microbiota were also associated with improvements in measurements related to glucose and lipid metabolism.
However, the results were not consistent in all preparations. Both the material studied and the way it was processed seemed to influence the result.
The polysaccharides of black mulberry fruit offer an example. The researchers used different extraction techniques to produce fractions with different structures and different levels of utilization by gut microbes. Fractions produced by water and pectate lyase extraction showed the strongest prebiotic potential.
Studies with mulberry leaf polysaccharides also suggest that structural characteristics are important. Characteristics such as molecular weight and monosaccharide composition can determine which bacteria can use the compounds as a substrate and which short-chain fatty acids are ultimately produced.
Combined mulberry compounds show stronger effects in mice
Some of the most intriguing findings came from experiments with more complex mulberry preparations.
In mice fed a high-fat diet, a fraction containing white mulberry polyphenols and polysaccharides produced more favorable changes in the gut microbiota than either fraction administered alone. These microbial changes were accompanied by improvements in some measures related to metabolic syndrome and intestinal health.
The researchers also performed a microbiota transplant experiment using the same model. The intestinal microbiota of mice that had received the combined mulberry fraction was transferred to other animals. Those receptors also showed improvements in some metabolic alterations, adding evidence that changes in the microbiota may help drive the effects of the blackberry preparation.
“These findings suggest that what is important 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. Therefore, instead of looking for a single universal product, it is worth determining which combination of species, plant parts, composition and processing method produces a specific biological effect,” emphasizes Professor Anna Prescha.
The research began with an idea from a student
The project arose from the student research group Nutri-Sfera of the Department of Dietetics and Bromatology of the Medical University of Wroclaw.
The topic was proposed by two graduate students: Marta Miszczak from the Dietetics major and Karolina Kłosowska-Buryło from the Pharmacy major. Their participation brought together nutritional and pharmaceutical approaches to study mulberry and intestinal microbiota.
“This fitted very well with the interdisciplinary nature of the study. It combined a perspective on mulberry as a plant material with a specific composition with an analysis of its possible effects on the microbiota and metabolism,” adds Professor Prescha.
Studies in humans are still lacking
Despite promising experimental findings, an important question remains unresolved. Researchers have not yet conducted human studies that directly examine how mulberry preparations affect the gut microbiota.
Most of the existing evidence comes from animal models and in vitro experiments. Comparing results between studies is also difficult because relatively few investigations combine biological findings with detailed chemical analysis of the exact mulberry preparation being tested.
“The available results are promising, but at the moment they do not allow us to determine whether the relationships observed in experimental models between mulberry preparations, microbiota and metabolism also occur in humans,” says Professor Prescha.
The researchers say clinical trials will need to use carefully characterized and standardized mulberry preparations. Such studies could help determine how different products affect the human gut microbiota, how large those effects are, and whether they result in measurable health benefits.
Did you know?
Mulberry leaves and fruits contain different compounds. The leaves contain, among other substances, DNJ, which is associated with carbohydrate metabolism, while the fruit of the black mulberry is especially rich in anthocyanins.
Processing can change the biological effects of mulberry. Even preparations made from the same part of the plant can behave differently depending on the extraction or fermentation method.
In experimental studies, combining compounds sometimes produced stronger effects than using them alone. In mice, a combination of white mulberry polyphenols and polysaccharides produced greater beneficial changes in the microbiota than either fraction alone.
The gut microbiota may also help mediate these effects. In one experiment, the transfer of microbiota from mice receiving a mulberry preparation to other animals was associated with improvements in some metabolic alterations.
The biggest unanswered question is whether these findings apply to people. No human studies have yet directly tested how blackberry preparations affect the gut microbiota.