Urolithins are microflora human metabolites of dietary ellagic acid derivatives such as ellagitannins. They are produced in the human gut, and found in the urine in the form of urolithin B glucuronide after absorption of ellagitannins-containing food such as pomegranate, strawberries, red raspberries, walnuts or oak-aged red wine.

During intestinal metabolism by bacteria, ellagitannins and punicalagins are converted to urolithins, which have unknown biological activity in vivo in humans. Urolithins metabolites of pomegranate juice ellagitannins localize specifically in the prostate gland, colon, and intestinal tissues of mice.

Ellagitannins exhibit low bioavailability and are transformed in the gut to ellagic acid and its microbiota metabolites. Urolithins are found in plasma mostly as glucuronides at low concentrations.

Urolithins production is dependent on the gut microbiome enterotype. Individuals producing urolithins show a much higher abundance of the Clostridium leptum group of Firmicutes phylum than Bacteroides or Prevotella.