“…They include (i) two fatty acids, 22 lipids (including gluco-, glycero-and glycerophospho-lipids) and 10 bile acid derivatives, low levels of which have been reported to promote cell lipotoxicity and apoptosis and have an overall cathartic effect on the colon (Yoon et al, 2002;Senkal et al, 2011;Swann et al, 2011;Longato et al, 2012); (ii) five N-acyl amino acids or polyamides (including arachidoyl glycine, N-stearoyl proline, N-oleoyl (iso)leucine, N-stearoyl tyrosine and N-palmitoyl threonine), the absence of which promotes dysfunction in the regulation of host temperature, locomotion and inflammation (Tan et al, 2010); (iii) ferroxamine and five metabolites implicated in porphyrin and iron metabolism, the deficiency of which decreases the concentration of beneficial gut microbiota and induces iron deficiency anaemia (Dostal et al, 2014); (iv) 12 presumptive secondary metabolites and bioactive peptides, such as methionine enkephalin and a number of tripeptides, the metabolism failure of which has been shown to lead to failure in immune and neuroactive ligand-receptor interactions (Yoshimasa et al, 1982;Salzet and Tasiemski, 2001); (v) inosine, pseudouridine and hypoxanthine, nucleoside and purine derivatives, the depletion of which may negatively influence the initiation of translation and nucleic acid synthesis in human gut microbiota and in gut mucosal defence (Grimble, 1994); and (vi) six ceramide/sphingolipid derivatives, creatinine, N-acetylhistamine, glyoxylate and succinate-ceramide and creatinine deficits in the gut have been associated with liver and renal dysfunctions (Peral et al, 2002; Longato et al, . Notably, the production of the above metabolites was observed in patients carrying toxin + C. difficile strains (Supplementary Table 2).…”