The impact of silymarin on microbiota could be influenced by certain limitations in our study, notably the sequencing technique and batch incubation approach, which may not accurately differentiate between live and dead bacterial cells, potentially masking differences. Additionally, dosage variations across studies can affect results. In our approach, we utilized a relatively low but diet-relevant concentration of 50 µg mL -1 , which we previously carefully calculated and reasoned. At this dosage, the likelihood of silymarin exhibiting antimicrobial activity and altering microbial populations in the human gut is low because it does not reach the commonly reported minimum inhibitory concentrations. However, as shown in our results, this concentration of silymarin leads to suppressed or slower fermentation and triggers changes in the fermentation pathways, reflected by increased monomeric carbohydrate levels (glucose, trahalose) and amino acids, and decreased production of their downstream products SCFAs (including BCFAs). While SCFAs are typically beneficial for gut pH balance, mucosal health, and inflammation reduction, they can paradoxically rise in certain pathological conditions, such as in individuals with high BMI and diabetes. . This increase may be associated with changes in microbiota composition and enhanced energy extraction, which can be undesirable. Microbial imbalances are also key contributors to metabolic and liver diseases, including non-alcoholic fatty liver disease. The most expressed effect was seen in our study on BCFAs. These are derived from the fermentation of BCAAs including valine, leucine, and isoleucine. BCFAs can affect lipid metabolism and inflammatory responses in adipose tissue, playing a role in metabolic health. Previous studies suggest that BCFA levels are elevated in individuals with higher BMI and age, and are linked to proteolytic fermentation, which produces harmful metabolites like ammonia and p-cresol, particularly in older adults. These associated metabolites may principally affect the viability of colonic epithelial cells or promote genomic DNA damage. Notably, silymarin had a stronger effect on fermentation in healthy elderly individuals compared to younger subjects. Additionally, in the elderly, it exhibited a different spectrum of catabolic products, suggesting potential age-related differences in its activity. This underscores the need for well-designed studies to explore silymarin's effects across age groups, as no clinical trials have yet stratified populations to assess this.