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NutrInsight • Do we need dietary polyphenols for health?
• Genetic susceptibility of individuals
Figure 4 shows that several transporters and enzymes are needed for the uptake of polyphenols across the cells of the small and large intestine. Single nucleotide polymorphisms (SNP’s) have been detected for several of these such as Phase II enzymes (SULT, UGT) [Ginsberg et al., 2010], Phase I enzymes (CY P450) [Chen et al., 2011] and membrane transporters (MRP etc.). It is therefore possible that bioavailability of polyphenols will be different in different individuals according to their genetic make-up.
• Microbiota metabolism
Recent research has shown that colon microbiota metabolism of large hydrophylic polyphenol molecules leads to smaller, more lipophilic metabolites [Selma et al., 2009] that are generally better absorbed than the original compounds. This allows them to reach the bloodstream and tissues where they can exert relevant biological effects. The metabolic processes involved include flavonoid ring fission, glycoside de-conjugation, de-acylation, de-hydroxylation, de-carboxylation, de-methylation and methylation. Different phenolics can lead to similar metabolites, which can be considered biomarkers of colonic metabolism if they are subsequently absorbed [Selma et al., 2009].
The gut microbiota of different individuals can be very dissimilar and therefore the intestinal metabolism of specific food phenolics can differ from one subject to another. Subjects can be divided into producers or non-producers of certain metabolites and this might explain why they can be responders or non-responders to the effects of polyphenols [Braune et al., 2011]. Thus, the potential health effects of polyphenols can be diverse depending on the gut microbiota composition and activity of the individuals.
The newly discovered existence of human enterotypes (i.e. distinct and robust clusters) could explain the large variability seen in diet intervention studies and could explain why some people respond to the beneficial effects of nutrients, including polyphenols, and some do not. There are three main enterotypes and they can be considered analogous to blood groups. These three enterotypes are based on three genus gut bacteria: Bacteroides, Ruminococcus and Prevotella; and on their relative importance in the gut [Arumugam et al., 2011]. Fecal metagenomes of human gut microbiomes have been examined from 39 people in six countries with previously published data sets and have confirmed that the enterotypes are not nation or continent specific [Arumugam et al., 2011]. The enterotypes are mostly driven by species composition, but abundant molecular functions are not necessarily provided by abundant species, highlighting the importance of a functional analysis to understand microbial communities.
So the existence of a limited number of well-balanced host–microbial symbiotic states, which might respond differently to diet and drug intake, could be another major factor influencing the bioavailability of polyphenols at individual level.
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