Polyphenols are natural compounds found in plants, fruits, vegetables, cereals, tea, coffee and wine, and are split into two groups: flavonoids and nonflavonoids.
The beneficial properties of polyphenols are dependent on their bioavailability, which is low compared to micro and macronutrients.
Polyphenols and their biotransformation
The research group from Instituto de Salud Carlos III, Madrid, Spain, looked at the bioavailability of polyphenols and their impact on the human body.
“The bioavailability and effects of polyphenols greatly depend on their transformation by components of the gut microbiota,” the team said.
“Different studies have been carried out to understand the gut microbiota transformation of particular polyphenol types and identify the microorganisms responsible.”
However, they commented that despite both polyphenols and gut microbiota being studied extensively, not much is known about their relationship with each other.
The report comments that only a small percentage of dietary polyphenols, around 5-10% of total intake, are directly absorbed into the small intestine.
These polyphenols are then subjected to extensive Phase I (oxidation, reduction and hydrolysis) and Phase II (conjugation) biotransformations, which results in a series of water-soluble conjugate metabolites that are distributed to organs.
Colonic bacteria in the large intestine react with the remaining polyphenols.
Effects of dietary polyphenols
Previous studies have shown that polyphenols can be converted by the colonic microbiota to bioactive compounds that can affect the intestinal ecology and influence host health.
Animal and human studies have both shown that certain doses of selected polyphenols may change the gut microbial composition, which can help some bacterial groups thrive.
One report referenced in the review was an in-vitro study which used a batch-culture model of the distal region of the large intestine to suggest that flavan-3-ol monomers could be capable of influencing the large intestinal bacterial population.
Furthermore, this study found that the flavan-3-ol monomer (+)catechin sigificantly inhibited growth of Clostridium histolyticum and enhanced growth of E. coli and members of the Clostridium coccoides-Eubacterium rectale group, whilst the growth of Bifidobacterium and Lactobacillus spp. were unaffected.
Another study the review looked at was a human intervention study that suggested the consumption of red wine polyphenols significantly increased the number of Enterococcus, Prevotella, Bacteroides, Bifidobacterium, Bacteroides uniformis, Eggerthella lenta, and Blautia coccoides-E.rectale group.
The report noted that previous studies have also suggested polyphenols have potential benefits for immunity by reducing concentrations of the plasma C-reactive protein (CRP), which is a blood marker of inflammation.
Red wine polyphenols have suggested health benefits also, as they have been shown to reduce blood pressure, trigylcerides and high-density lipoprotein cholesterol.
The research team concluded their report by stating that dietary polyphenols are clear to contribute to the maintenance of gut health.
“It is clear that dietary polyphenols and their metabolites contribute to the maintenance of gut health by the modulation of the gut microbial balance through the stimulation of the growth of beneficial bacteria and the inhibition of pathogen bacteria, exerting prebiotic-like effects,” the team said.
More studies are needed to fully understand the health effects of polyphenols the group said.
Study: Benefits of polyphenols on gut microbiota and implications in human health
Source: The Journal of Nutritional Biochemistry
Published online, DOI: 10.1016/j.jnutbio.2013.05.001
Authors: Fernando Cardona, Cristina Andrés-Lacueva, Sara Tulipani, Francisco J. Tinahones, Maria Isabel Queipo-Ortuño