Changes in the level of select metabolites before NF. (A) A total of 310 serum metabolites were associated with NF, 51 metabolites were associated with abundance of gut Akkermansia, and 9 metabolites were associated with both. (B-I) Serum samples preceding vs not preceding NF within 24 hours were compared for select metabolites using Welch’s t test. (B-E) show colonic bacteria–derived metabolites from dietary tyrosine and tryptophan degradation. (F-H) show select metabolites in the γ-glutamyl cycle. Metabolites in (B-H) were measured by UPLC-MS/MS. GGT in (I) was measured fluorometrically. The boxplots show the median and interquartile range.