Microbial tryptophan catabolites (TCA) are metabolites produced by gut bacteria that influence host health and disease. These metabolites, such as indole, tryptamine, indolepropionic acid (IPA), and indolelactic acid (ILA), are generated through the degradation of dietary tryptophan by gut microbiota. They play a crucial role in host-microbial communication and affect various physiological processes, including immune regulation, intestinal barrier function, gut hormone secretion, and systemic inflammation. TCA can activate the aryl hydrocarbon receptor (AHR), which modulates immune responses and intestinal homeostasis. Some TCA, like IPA and ILA, have anti-inflammatory and antioxidant properties, while others, such as indoxyl sulfate (IS), may have toxic effects. TCA also influence gut motility and the production of gut hormones, such as glucagon-like peptide-1 (GLP-1), which regulates appetite and glucose metabolism. The gut microbiota's ability to produce TCA is influenced by diet, host genetics, and microbial interactions. While TCA have been shown to have beneficial effects in health, their role in disease, such as inflammatory bowel disease (IBD) and neurodegenerative disorders, is still being explored. Research is needed to better understand the mechanisms by which TCA affect host physiology and to develop strategies to modulate gut microbiota for therapeutic purposes. Future studies should focus on identifying the main TCA-producing bacteria in the human gut, understanding their interactions with the host, and exploring their potential as therapeutic targets.Microbial tryptophan catabolites (TCA) are metabolites produced by gut bacteria that influence host health and disease. These metabolites, such as indole, tryptamine, indolepropionic acid (IPA), and indolelactic acid (ILA), are generated through the degradation of dietary tryptophan by gut microbiota. They play a crucial role in host-microbial communication and affect various physiological processes, including immune regulation, intestinal barrier function, gut hormone secretion, and systemic inflammation. TCA can activate the aryl hydrocarbon receptor (AHR), which modulates immune responses and intestinal homeostasis. Some TCA, like IPA and ILA, have anti-inflammatory and antioxidant properties, while others, such as indoxyl sulfate (IS), may have toxic effects. TCA also influence gut motility and the production of gut hormones, such as glucagon-like peptide-1 (GLP-1), which regulates appetite and glucose metabolism. The gut microbiota's ability to produce TCA is influenced by diet, host genetics, and microbial interactions. While TCA have been shown to have beneficial effects in health, their role in disease, such as inflammatory bowel disease (IBD) and neurodegenerative disorders, is still being explored. Research is needed to better understand the mechanisms by which TCA affect host physiology and to develop strategies to modulate gut microbiota for therapeutic purposes. Future studies should focus on identifying the main TCA-producing bacteria in the human gut, understanding their interactions with the host, and exploring their potential as therapeutic targets.