The relationship between phenolic compounds from diet and microbiota: impact on human health.

The human intestinal tract is home to a complex microbial community called microbiota. This gut microbiota, whilst playing essential roles in the maintenance of the health of the host, is exposed to the impact of external factors such as the use of medication or dietary patterns. Alterations in the composition and/or function of the microbiota have been described in several disease states, underlining the role of the gut microbiota in keeping the health status. Among the different dietary compounds, polyphenols constitute a very interesting group as some of them have been found to possess important biological activities, including antioxidant, anticarcinogenic or antimicrobial activities. The term polyphenol comprises thousands of molecules presenting a phenol ring and are widely distributed in plant foods. The bioactivity of these compounds is highly dependent on their intestinal absorption and often they are ingested as non-absorbable precursors that are transformed into bioactive forms by specific microorganisms in the intestine. Some of these microorganisms have been identified and the enzymatic steps involved have been elucidated. However, little is known about the impact of these ingested polyphenols upon the human gut microbiota. The heterogeneity of the polyphenol compounds and their food sources, as well as their coexistence with other bioactive compounds within a normal diet, together with the complexity of the human gut microbiota make difficult the understanding of the interactions between dietary polyphenols and gut microbes. This is, however, an important area of research which promises to expand our knowledge on the food functionality area through understanding the microbiota-food component interaction.