Dietary
intake of plant polyphenols is significant, and many of
them enter a human body as a highly diverse pool of ring-fission phenolic
metabolites arising from digestion and microbial catabolism of the
parental structures. Difficulty in designing the uniform intervention
studies and limited tools calibrated to detect and quantify the inherent
complexity of phenolic metabolites hindered efforts to establish and
validate protective health effects of these molecules. Here, we highlight
the recent findings that describe novel complex downstream metabolite
profiles with a particular focus on dihydrophenolic (phenylpropanoic)
acids of microbial origin, ingested and phase II-transformed methylated
phenolic metabolites (methylated sinks), and small phenolic metabolites
derived from the breakdown of different classes of flavonoids, stilbenoids,
and tannins. There is a critical need for precise identification of
the individual phenolic metabolite signatures originating from different
polyphenol groups to enable future translation of these findings into
break-through nutritional interventions and dietary guidelines.