Tryptophan catabolism by gut microbiota : A bridge connecting food science and human nutrition

Effects of various whole foods on the production of tryptophan-derived aryl hydrocarbon receptor (AhR) ligands in the intestine were investigated in a pig model.Ileal digesta and faeces of pigs after feeding of eighteen different foods were analyzed.Indole, indole-3-propionic acid, indole-3-acetic acid, indole-3-lactic acid, kynurenine, tryptamine, and indole-3-aldehyde were identified in ileal digesta, which were also identified in faeces but at higher concentrations except indole-3-lactic acid, together with skatole, oxindole, serotonin, and indoleacrylic acid.The panel of tryptophan catabolites in ileal digesta and faeces varied across different foods.Eggs induced the highest overall concentration of catabolites in ileal digesta dominated by indole.Amaranth induced the highest overall concentration of catabolites in faeces dominated by skatole.Using a reporter cell line, we observed many faecal samples but not ileal samples retained AhR activity.Collectively, these findings contribute to food selection targeting AhR ligands production from dietary tryptophan in the intestine.