We report on the metabolism of the polyphenols known as ellagitannins in humans for the first time. The paper highlights that this metabolism greatly depends on each person’s specific intestinal bacteria.

“Our current research tries to identify whether a high or low urolithin production is good.”

This study identifies the human colonic microflora-derived metabolites "urolithins" as biomarkers of human exposure to dietary ellagitannins, independently of their chemical structure.

Ellagitannins—abundant in strawberries, raspberries, walnuts, etc.—have been acknowledged to have both antioxidant and cancer chemopreventive activities. Ellagitannins are extensively processed (metabolized) by the intestinal bacteria yielding other molecules so-called "urolithins."

Each person carries specific intestinal bacteria which contain a high or low capacity to produce these urolithins. The activity of the ingested ellagitannins should be considered as taking place in the gastrointestinal tract, whereas the possible effects in other parts of the body should be due to these urolithins. Therefore, depending on the person, any possible biological activity of ellagitannins can be quite different.

Polyphenols are very abundant in plant foods. These molecules are involved in the sensory quality of fruits and vegetables—color, taste, texture, etc. In the last several years, dietary polyphenols have attracted attention due to their role in the prevention of some diseases—such as cancer and cardiovascular and neurodegenerative diseases.

This study is part of a broader research effort involving the metabolism and biological activity of dietary polyphenols—including ellagitannins—in animal models and humans.

Our study suggests that, depending on the colonic microflora of each individual, high or low ellagitannin metabolism can occur and thus, differing levels of urolithin production will be the result. This could imply that the biological activity of ellagitannins can be quite different depending on each person. Our current research tries to identify whether a high or low urolithin production is good. Within this context, the biological activity of urolithins is under examination along with the identification of intestinal bacteria involved in their production.