Researchers from Italy and Austria assessed the bioavailability of phenol and polyphenol compounds from three capsules each containing 750mg fruit and vegetable extracts in a group of 20 people.
Writing in Nutrients, they showed significant variation in how they absorbed phenolics and produced metabolites – adding that the variances are likely due to differences in gut microbiota between individuals which should be taken into account in future research investigating the effect of polyphenols and other plant nutrients on health.
“Out of the 92 monitored molecules, 20 quantifiable metabolites were identified, or tentatively identified in plasma samples,” wrote the researchers. “As expected, detected metabolites derived from different (poly)phenols and appeared at different times in plasma.”
In contrast, the team found flavanone metabolism occurred mainly in the large intestine.
The team claims the findings are the first to report concentrations of patuletin and myricetin metabolites – and also report detection of ‘a new flavone metabolite’ in the form of diosmetin sulfate, derived from diosmin.
However, they failed to find metabolites associated with flavan-3-ols, which were abundant in one of the capsules – noting that previous research has shown these compounds are degraded by gut bacteria into hydroxyphenyl-γ-valerolactones.
Gut bacteria change absorption patterns
“A clear example of this large variability among participants concerns the circulating concentration of phenyl-γ-valerolactones resulting from the catabolic transformations of catechins and procyanidins, operated mainly by Clostridium coccoides and Bifidobacterium spp,” they wrote.
The team reported five subjects that were abundant producers of phenyl-γ-valerolactones, while the rest produced only very small amounts.
They also found variation in the timing of metabolite appearance in blood plasma, with kaempferol glucuronide metabolites disappearing after five or 10 hours for all but two subjects, who showed a later peak, “probably due to colonic absorption”.
“Considering this large variability, there is an increased interest in stratifying future study participants based on their polyphenol-metabolizing phenotypes (i.e., metabotypes), and the present study supports the hypothesis that this variability should be carefully considered as a confounder of in vivo studies evaluating health effects of these phytochemicals.”
Published online ahead of print, doi: 10.3390/nu9030194
“Absorption Profile of (Poly)Phenolic Compounds after Consumption of Three Food Supplements Containing 36 Different Fruits, Vegetables, and Berries”
Authors: Bresciani, L, et al