Two publications demonstrate the importance of colonic microbiota in formation of circulating metabolites in human body.
Review article Aura (2008) deals with microbial metabolism of dietary phenolic compounds, which reach the colon as enclosed in dietary fibre matrix from plant foods such as berries, fruits and wholegrain products. A vast knowledge was already gathered in 1960´s to 1980´s of microbial metabolism of xenobiotic compounds, including dietary phenolics, after which the interest was focused on antioxidant activities of these compounds. However, demonstration of antioxidant activity has been demanding, because the compounds disappear from circulation and a diverse metabolite pool appears to be circulating in the body. Microbial metabolites have been shown from in vitro incubations with animal or human faecal microbiota and the same metabolites were also found in human plasma and urine. Novel tools using metabolomic platforms enable observation of the whole metabolome instead of limited number of expected metabolites.