This 24-week trial took place in China and assigned 83 participants to either placebo or 103.2 mg/day silymarin (split into two daily doses, given at breakfast and dinner). The primary outcomes were markers of liver health, including liver stiffness, hepatic steatosis, and liver function, with M probe vibration-controlled transient elastography (VCTE, FibroScan) utilized to assess steatosis and stiffness. A number of markers of metabolic health were included as secondary outcomes, including body composition and glucose and lipid profiles, as well as 16S rRNA sequencing of fecal samples.
Compared to baseline participants receiving silymarin had a significant reduction in liver stiffness (-0.21 kPa) while people receiving placebo had a tendency to increase (+0.41 kPa). Significant reductions in serum γ-glutamyl transpeptidase (GGT) and ApoB also occurred with silymarin, in contrast to increases with placebo. No other significant differences were observed, although silymarin was linked to changes in the gut microbiome, specifically to increased species diversity and enrichment of Oscillospiraceae and decreased Selenomonadaceae abundance. Oscillospiraceae species may have the ability to metabolize complex carbohydrates and synthesize short-chain fatty acids, suggesting a possible gut-liver axis for the observed benefits. Overall, this study supports a protective effect of silymarin against liver stiffness at fairly low doses, as well as reductions in GGT and ApoB (both associated with overall mortality in multiple other studies), in support of a recent meta-analysis evaluating polyphenol use for NAFLD.