I love this article by biomedica which gives instights on how chemicals found in plant foods such as polyphenols and prebiotics, fuel for our gut microbiome help our gastrointestinal tract (GIT) and therefore our health. More proof on how important our gut health is!

Polyphenols and prebiotics: A synergistic GIT therapy

Plant polyphenols found in fruits, vegetables, and grains play an important role in human health via their ability to reduce oxidation in conditions such as obesity, diabetes, and cardiovascular disease.

What do the polyphenols do?

Polyphenols get metabolised by the gut bacteria, and these phenolic gut metabolites act on their target cells and positively influences metabolic health outcomes. Polyphenols positively influence the gut microbiome which then favourably alters metabolic disease. Consuming both prebiotics and polyphenols can enhance the efficacy and efficiency of both therapies.

Polyphenols are secondary metabolites found in plants and are particularly abundant in fruits, vegetables, and grains. Grouped according to their chemical structure, they include lignans, phenolic acids, stilbenes, tannins, and flavonoids. Polyphenols are important to include in our diet because of their antioxidant, and it has been shown to help reduce oxidation in conditions such as obesity, diabetes, and cardiovascular disease.

Only about 5-10% of total ingested polyphenols are absorbed in the small intestine because of their complex chemical makeup and high molecular weight. These absorbable and less complex polyphenols undergo various de-conjugation reactions and metabolism in the small intestine. The remaining 90-95% of ingested polyphenols reach the colon in an unchanged form. Here, the gut microbiota plays a significant role in their metabolism and absorption.

Interaction between the gut microbiota and polyphenols 

Studies show that there is a complex interaction between the gut microbiota and the polyphenols and the retention of polyphenols in the gastrointestinal tract can have beneficial effects on the microbiome, exerting prebiotic-like activity whilst simultaneously resulting in the biotransformation of polyphenols into active metabolites.

A recent review published in Nutrients evaluates the current evidence on the effect of common polyphenols – curcumin, quercetin and catechins – on the gut microbiota, and their subsequent impact on gut and metabolic health.

Various bacteria, including Lactobacillus and Bifidobacterium species, are involved in the biotransformation of curcumin, quercetin and catechins into their various bioactive metabolites via enzymes produced by the gut microbiota. Bacterially synthesised metabolites then reach the liver via the portal vein, where they undergo further metabolism, following which they reach their target tissues and cells.

Conversely, polyphenols exert various effects on the gut microbiome. Curcumin has been found to influence microbial diversity and composition while also positively influencing intestinal barrier function. Studies have found that orally administered curcumin reduces diet-induced lipopolysaccharide levels, while also modulating bacteria associated with a dysbiotic picture, including an imbalanced Firmicutes/Bacertoidetes ratio.

Quercetin has been found to reduce levels of various pathogenic bacteria, including E. coli, Enterococcus and Fusobacterium while promoting the growth of Lactobacillus and Bifidobacterium species. Catechins found in green tea, specifically EGCG, EGC and GCG, have similarly been found to reduce various strains of pathogenic bacteria, including H. Pylori while supporting the growth of Bifidobacterium species.

The authors noted that it may be the influence on microbial diversity that, in part, results in favourable impacts to metabolic disease from the use of polyphenol containing supplements.

It is important to note that human studies are limited, with the majority of research being conducted in vivo or in animals. Furthermore, the use of polyphenols as a prebiotic is directly influenced by the residing bacterial strains. However, the authors conclude that the co-administration of prebiotics with polyphenols may be helpful to enhance the efficacy and efficiency of both therapies.

References

Shabbir, U., Rubab, M., Daliri, E. B. M., Chelliah, R., Javed, A., & Oh, D. H. (2021). Curcumin, quercetin, catechins and metabolic diseases: The role of gut microbiota. In Nutrients (Vol. 13, Issue 1, pp. 1–24). MDPI AG. https://doi.org/10.3390/nu13010206
Gowd, V., Karim, N., Shishir, M. R. I., Xie, L., & Chen, W. (2019). Dietary polyphenols to combat the metabolic diseases via altering gut microbiota. In Trends in Food Science and Technology (Vol. 93, pp. 81–93). Elsevier Ltd. https://doi.org/10.1016/j.tifs.2019.09.005
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