a–d Total BAs and total HCA species in serum and feces of healthy control (C, n = 26), pre-diabetes (preDM, n = 30) and diabetes (DM, n = 35) groups. e–j Individual HCA species in the three groups in all (n = 91), male (n = 35) and female (n = 56) samples. k, l Heatmaps of Spearman correlation coefficients of total and individual HCA species in serum and feces with representative metabolic markers. Data are expressed as median with interquartile range (a–j). In the bar plots (a–j), * and # indicate the statistical significance (p < 0.05) between two groups and among three groups, respectively, based on two-sided Kruskal–Wallis test. In the heatmaps (k, l), r value indicates Spearman correlation coefficient, and * indicates the statistical significance (p < 0.05) based on Spearman correlation. HCA species in serum is the concentration summation of HCA, HDCA, GHCA, and GHDCA. HCA species in feces is the concentration summation of HCA and HDCA.