Figure 1.

Serum cortisol fully mediates the relationship between fecal Ruminococcus and MRS-derived brain N-acetylaspartate. First, fecal Ruminococcus negatively predicted MRS-derived brain NAA concentrations (path A). Second, fecal Ruminococcus negatively predicted serum cortisol concentrations (path B). Third, mediation effects were assessed for serum cortisol concentrations. The indirect effect (i.e., the effect of fecal Ruminococcus through serum cortisol on MRS-derived brain NAA; path B × C) was significant, and the direct effect (path A’) was not significant. Thus, serum cortisol fully mediates the relationship between fecal Ruminococcus and MRS-derived brain NAA. Abbreviation: N-acetylaspartate (NAA).