Bioactive compounds such as polyphenols and their potential health benefits have long attracted public attention and interest. Polyphenols, commonly found in plant-based foods such as fruits, vegetables, seeds, coffee, and tea, have a strong bitter taste and are typically poorly absorbed and therefore excreted from the body.
Polyphenols interact with human bitter taste receptors, also known as type 2 taste receptors (T2R), which are expressed in and around the oral cavity. In particular, activation of T2Rs expressed along the gastrointestinal tract is implicated in the bioactivity of ingested polyphenols. The scientific mechanisms beyond T2R activation that lead to the reported health benefits of polyphenols are unknown. With over 8,000 polyphenols and 25 human T2Rs, this is a significant gap in knowledge.
Focused on bridging this gap, a research team led by Professor Naomi Nagabe of Shibaura Institute of Technology, together with Dr. Makoto Omoto of Takasaki University of Health and Welfare, Dr. Yasuyuki Fujii and Dr. Takafumi Shimizu of Shibaura Institute of Technology, Dr. Keiko Abe of the University of Tokyo, and Dr. Vittorio Calabrese of the University of Catania, Italy, conducted a review to understand the interactions between polyphenols and T2R and the resulting health effects. Their findings were published in the journal Food Bioscience on June 18, 2024.
Professor Osakabe emphasizes, “Although polyphenols have a low absorption rate, there are reports that they improve glucose tolerance. The mechanism of this effect is still unknown, and we are currently investigating the relationship between polyphenol intake and the risk of type 2 diabetes.”
This review focuses on the mechanisms of communication between polyphenols, T2Rs, and brain centers regulating glucose homeostasis and appetite. Polyphenol-mediated binding and activation of T2Rs in the gut promotes the secretion of gut hormones such as cholecystokinin (CCK) and incretins. Incretins include glucose-dependent insulinotropic polypeptide and glucagon-like peptide-1 (GLP-1), which induce insulin secretion and regulate blood glucose homeostasis. CCK and GLP-1 regulate appetite and food intake by affecting gut motility. Polyphenol-induced gut hormones reduce the risk of obesity and diabetes.
Professor Osakabe explains, “Gut hormones are known to regulate feeding behavior and maintain glucose tolerance via the endocrine and nervous systems. Therefore, the bitterness of polyphenols may reduce the risk of diabetes and its complications through T2R activation.”
Overall, the findings suggest that ingested polyphenols, although remaining unabsorbed, promote the secretion of gut hormones by activating bitter taste receptors expressed in gastrointestinal secretory cells, thereby regulating blood glucose levels and appetite. Professor Osakabe concludes, “Our study highlights the importance of ingesting polyphenols to reduce the risk of obesity and diabetes by regulating blood glucose levels and appetite.”
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Shibaura Institute of Technology
Journal References:
Osakabe, N., et al. (2024). Beneficial physiological activities of bitter polyphenols via gastrointestinal hormones. Food Bioscience. doi.org/10.1016/j.fbio.2024.104550.
