Urobilinogens comprise a mixture of bilirubin metabolites, including D-urobilinogen, L-urobilinogen (stercobilinogen), and i-urobilinogen (mesobilirubinogen). These compounds are produced from bilirubin by gut microbiota. In mice on a high-fat diet, the cecal concentrations of D-urobilinogen, L-urobilinogen, and i-urobilinogen are increased. Furthermore, elevated fecal levels of L-urobilinogen are inversely associated with reduced blood hemoglobin levels in patients with heterozygous β-thalassemia.