Why researchers are studying mulberries and gut health

“The gut microbiota not only contributes to the functioning of the gastrointestinal tract, but can also influence the metabolism of the entire body. Mulberries are particularly interesting in this respect, as they contain a large number of bioactive compounds, such as polyphenols and polysaccharides, that can interact with gut microorganisms,” explains Anna Preša, Ph.D., Ph.D., Professor, Department of Nutrition and Bromine Sciences, Medical University of Wrocław.

Different mulberry varieties contain different compounds

Research to date has mainly focused on white mulberry (Aruba) and black mulberry (Nigra), particularly its fruit, which has produced notable results.

Mulberry leaves contain several biologically active substances, including 1-deoxynojirimycin (DNJ), a compound known to affect carbohydrate metabolism. They also contain polyphenols and polysaccharides. Black mulberry fruit, on the other hand, contains high levels of anthocyanins and other phenolic compounds, as well as polysaccharides.

How the plant material is processed can also make a significant difference. Drying, fermentation and extraction methods can change the amount and relative proportions of bioactive compounds. As a result, two formulations made from the same plant material may differ considerably in composition and biological effects.

Mulberry preparations may change gut bacteria

The review found that preparations made from both mulberry leaves and fruits can influence the composition and activity of the gut microbiota. Several studies have reported beneficial changes in bacterial populations associated with increased production of short-chain fatty acids, including acetate, propionate and butyrate.

These compounds are produced when intestinal microorganisms ferment food substances 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 across all preparations. Both the plant material studied and the way it was processed appeared to influence the outcome.

Extraction methods can affect prebiotic potential

Black mulberry fruit polysaccharides provide one example. Researchers used different extraction techniques to produce fractions with different structures and levels of utilization by gut microbes. Fractions generated using water extraction and pectate lyase showed the strongest prebiotic potential.

Studies on mulberry leaf polysaccharides also suggest that their structural features are important. Characteristics such as molecular weight and monosaccharide composition may determine which bacteria can use a compound as a substrate and which short-chain fatty acids are ultimately produced.

Combined mulberry compounds produced stronger effects in mice

Some of the most interesting findings came from experiments involving more complex mulberry preparations.

In mice fed a high-fat diet, a fraction containing both polyphenols and polysaccharides from white mulberry fruit produced more favorable changes in the gut microbiota than either fraction alone. These microbial changes were accompanied by improvements in several measurements related to metabolic syndrome and gut health.

The researchers also conducted microbiota transplantation experiments using the same model. The gut microbiota of mice given the combined mulberry fractions was transferred to other animals. The recipient animals also showed improvements in some metabolic disorders, providing additional evidence that microbiome changes may help mediate the effects of mulberry preparations.

“These findings suggest that it is not only the presence of individual compounds that is important, but 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 combinations of species, plant parts, composition and processing methods produce specific biological effects,” emphasizes Professor Anna Preša.

The project began with a student research idea

The project began within the Nutri-Sfera student research group at the Faculty of Nutrition and Bromology at the Medical University of Wrocław.

The topic was proposed by two students who have since graduated: Marta Miszczak, who studied nutrition, and Karolina Kłosowska-Bryło, who studied pharmacy. Their involvement brought together nutritional and pharmaceutical approaches to studying mulberry and the gut microbiota.

“This fit very well with the interdisciplinary nature of the study, combining the perspective of mulberry as a plant material with a specific composition and the analysis of its potential effects on the microbiome and metabolism,” added Professor Preša.

Human studies on mulberry and the gut microbiome are still lacking

Despite the promising experimental findings, one major question remains unanswered: how do mulberry preparations affect the human gut microbiome?

Researchers have not yet conducted human studies that directly investigate this question. Most of the available evidence comes from animal models and laboratory experiments. Comparing results across studies is also difficult because relatively few investigations have combined biological testing with detailed chemical analysis of the exact mulberry preparations used.

“Although the available findings are promising, at this stage it is not possible to determine whether the relationships between mulberry preparation, microbiota and metabolism observed in experimental models also occur in humans,” Professor Preša points out.

Researchers say future clinical trials should use carefully characterized and standardized mulberry preparations. Such studies could help determine how different products affect the human gut microbiome, how large the effect is and whether it produces measurable health benefits.

Key facts about mulberries and gut health

• Mulberry leaves contain DNJ, a compound involved in carbohydrate metabolism.
• Black mulberry fruit is particularly rich in anthocyanins and other phenolic compounds.
• Drying, fermentation and extraction can change the biological effects of mulberry preparations.
• Compounds from mulberry may work differently when used together than when used individually.
• In mice, a combination of polyphenols and polysaccharides from white mulberry fruit produced greater beneficial changes in the microbiota than either fraction alone.
• Transferring the microbiota of treated mice to other animals was associated with improvements in some metabolic disorders.
• No human studies have yet directly tested how mulberry preparations affect the gut microbiome.