Polyphenols are one of the largest groups of phytochemicals found in fruits, vegetables, cereals, legumes, tea, coffee, cocoa, and wine. These compounds have attracted considerable attention due to their antioxidant, anti-inflammatory, antimicrobial, and cardioprotective properties, as well as their potential role in the prevention of chronic diseases such as cardiovascular disease, diabetes, neurodegenerative disorders, and certain types of cancer¹,².
However, the health effects of dietary polyphenols depend not only on their concentration in foods but also on their bioavailability, which is defined as the proportion of an ingested compound that is absorbed, metabolized, reaches the systemic circulation, and becomes available to exert biological activity in the body³. Consequently, evaluating polyphenol bioavailability is essential for understanding their physiological effects and designing functional foods with improved efficacy.
The absorption of polyphenols is a highly complex process that is largely determined by their chemical structure and interactions with the food matrix. Low-molecular-weight compounds, such as phenolic acids and flavonoid aglycones, can be absorbed directly through the small intestine, whereas glycosylated flavonoids and polymeric polyphenols require hydrolysis by intestinal enzymes or microbial metabolism before becoming absorbable3,4. In addition, the release of polyphenols from the food matrix during digestion could be influenced by processing conditions, pH variations throughout the gastrointestinal tract, and interactions with dietary fibers, proteins, and lipids5. These factors may either increase or decrease the amount of polyphenols available for intestinal absorption, explaining the considerable variability observed among different food sources.
Following absorption, polyphenols undergo extensive biotransformation in the cells, consequently, the metabolites detected in plasma and tissues differ substantially from the original compounds present in foods. Polyphenols that are not absorbed in the small intestine reach the colon, where they are metabolized by the gut microbiota into a wide range of low-molecular-weight phenolic metabolites. These microbial-derived metabolites are often more readily absorbed and may contribute significantly to the biological effects associated with polyphenol-rich diets2,6.
Furthermore, growing evidence indicates that the relationship between polyphenols and the gut microbiota is bidirectional, with polyphenols modulating microbial composition while microbial communities determine the formation of bioactive metabolites7.
Despite the substantial evidence supporting the beneficial effects of dietary polyphenols, their generally low bioavailability remains one of the major challenges for translating in vitro findings into clinical outcomes4. Current research has therefore focused on developing strategies to improve polyphenol stability, bioaccessibility, and intestinal absorption, including encapsulation technologies, nanoemulsions, lipid-based delivery systems, and the use of proteins and polysaccharides as protective carriers8. In parallel, advances in metabolomics, food processing technologies, and microbiome research have provided new insights into the mechanisms governing polyphenol metabolism and biological activity. A deeper understanding of these processes is fundamental for the development of functional foods and nutraceuticals capable of maximizing the health-promoting potential of dietary polyphenols.
References
1) Scalbert, A., et al. (2005). Polyphenols: Antioxidants and beyond. Am J Clin Nutr. https://doi.org/10.1093/ajcn/81.1.215S
2) Del Rio, D., et al. (2013). Dietary (poly)phenolics in human health: Structures, bioavailability, and evidence of protective effects against chronic diseases. Antioxid Redox Signal. doi:10.1089/ars.2012.4581
3) Manach, C., et al. (2004). Bioavailability and bioefficacy of polyphenols in humans. I. Review of 97 bioavailability studies. Am J Clin Nutr. https://doi.org/10.1093/ajcn/79.5.727
4) Williamson, G., & Clifford, M. N. (2017). Role of the small intestine, colon and microbiota in determining the metabolic fate of polyphenols. Biochem Pharmacol. doi:10.1016/j.bcp.2017.03.012
5) Bohn, T. (2014). Dietary factors affecting polyphenol bioavailability. Nutr Rev. doi:10.1111/nure.12114
6) Selma, M. V., et al. (2009). Interaction between phenolics and gut microbiota: Role in human health. J Agric Food Chem. doi:10.1021/jf902107d
7) Cardona, F., et al. (2013). Benefits of polyphenols on gut microbiota and implications in human health J Nutr Biochem. doi:10.1016/j.jnutbio.2013.05.001
8) McClements, D. J. (2020). Delivery by design (DbD): A standardized approach to the development of efficacious nanoparticle- and microparticle-based delivery systems. Compr Rev Food Sci Food Saf. doi:10.1111/1541-4337.12313
