Categorization based on the fecal BAs composition
We categorized the participants of the study based on their fecal BAs composition by combining cluster analyses and tertiles. The 17 types of BA concentrations we analyzed were subjected to subsequent cluster analysis [including five free BAs (CA, CDCA, DCA, LCA, and ursodeoxycholic acid (UDCA)), five glycine conjugated (G-) BAs (G-CA, G-CDCA, G-DCA, G-LCA, and G-UDCA), five taurine conjugated (T-) BAs (T-CA, T-CDCA, T-DCA, T-LCA, and T-UDCA), 7-oxo-DCA, and 7-oxo-LCA]. The data matrix is presented as Online Resource 1. We used non-standardized variables because they were all on the same scale (µmol/g), and the data were comparable. First, we determined the number of clusters through the tree diagram, which is generated using the squared Euclidean distance via the ward’s method [The fecal bile acid levels were measured per fresh fecal mass and were therefore affected by the fecal water content. Thus, we analyzed the categorization scheme generated by the cluster analysis, which also included the BSFS type of feces used in the analysis as a variable. Two-step cluster analysis, which can also handle categorical variables, was used. All categories obtained by cluster analysis including the BSFS type were identical, with the exception of one participant’s classification (see Online Resource 2), and the results of subsequent analyses were similar. All cluster analyses were performed using the Statistical Package for the Social Sciences Software Ver. 28.0 for Windows (IBM SPSS 28 Statistics Base, Inc., Chicago, IL, USA).