Human Metabolome Database (HMDB): Indole-3-propionic acid (IPA, indole-3-propionate, or indolepropionic acid), is a deamination product of tryptophan formed by symbiotic bacteria in the gastrointestinal tract of mammals and birds. It is endogenously produced by human microbiota and has only been detected in vivo when the species Clostridium sporogenes is present in the gastrointestinal tract (PMID: 19234110). Indole-3-propionic acid is an even more potent scavenger of hydroxyl radicals than melatonin, the most potent scavenger of hydroxyl radicals that is synthesized by the human body. Similar to melatonin but unlike other antioxidants, indole-3-propionic acid scavenges radicals without subsequently generating reactive and pro-oxidant intermediate compounds (PMID: 9928448). Indole-3-propionic acid has been shown to prevent oxidative stress and death of primary neurons and neuroblastoma cells exposed to the amyloid beta-protein in the form of amyloid fibrils, one of the most prominent neuropathologic features of Alzheimer's disease. Indole-3-propionic acid also shows a strong level of neuroprotection in two other paradigms of oxidative stress. (PMID: 10319516). More recently it has been found that higher indole-3-propionic acid levels in serum/plasma are associated with reduced likelihood of type 2 diabetes and with higher levels of consumption of fiber-rich foods (PMID: 28397877).