Fig. 2

Summary of targeted measurements of short chain fatty acids in human plasma after fasting. a Change in fasting circulating (plasma) concentrations [μM] for the three major short chain fatty acids (SCFAs). Line ranges summarize the 95% within-group confidence interval (Wilcoxon Rank Sum test [37]), with nominal significance indicated above the respective group (star) or between-group comparison (bracket with star). Single and double stars indicate the one-sided significance of p < 0.05 and p = 0.007, respectively. b Scatter plot of human plasma butyrate [μM] versus fecal butyrate [mM] corresponding to specimens collected at the same clinical visit. Line indicates the robust linear regression [36], with a green shading and p-value shown for the only slope coefficient to reach nominal significance, p = 0.003. c Scatter plot of the change in participant HbA1c versus their change in plasma butyrate [μM]. Due to the confounding variable of SFU drug use (see below), participants using SFU drugs are highlighted in gray and omitted from the robust linear regressions. In both (b) and (c) the gray ribbon denotes the 95% confidence region for the linear regression. d Heatmap of Spearman’s correlation between the participant-wise changes in metabolic measures (top seven rows) and major SCFAs (bottom three rows). Correlations were separately estimated for each study arm. Correlation magnitude and direction is indicated by the provided color shading legend. ‘AUC_inc’ and ‘AUC_tot’ prefixes correspond to the incremental and total area under the curve of the oral meal tolerance test, respectively. For clarity, correlations with nominal p > 0.4 are set to zero (white color shading) irrespective of incidental correlation value