Role of Bitter Polyphenols in the Regulation of Blood Sugar

Researchers evaluate how unabsorbed dietary polyphenols can regulate blood glucose levels and appetite through secretion of gastrointestinal hormones

Polyphenols remain unabsorbed by the body, yet they impact glucose homeostasis. With this in mind, researchers from Japan and Italy explored the mechanism by which polyphenols improve glucose tolerance.  They found that polyphenols bind to bitter taste receptors expressed along the gut and promote secretion of hormones that communicate with the brain, regulating blood glucose and satiety. Their findings endorse consumption of polyphenols to reduce risk of obesity and diabetes.

 

---

Bioactive compounds like polyphenols and their health benefits have long captured public attention and interest. Commonly present in plant-based food like fruits, vegetables, seeds, coffee, and tea, the polyphenols have a strong bitter taste and, in the normal course, is excreted by our body due to poor absorption. 

The polyphenols interact with human bitter taste receptors also known as Type 2 taste receptors (T2R) expressed within and outside the oral cavity. Notably, the activation of T2R expressed along the gastrointestinal (GI) tract is responsible for the bioactivity of ingested polyphenols. The scientific mechanisms beyond T2R activation leading up to the reported health benefits of polyphenols are unclear. With over 8,000 types of polyphenols and 25 types of human T2R, this is a crucial gap in knowledge. 

With a focus to fill in this gap, a team of researchers led by Professor Naomi Osakabe from Shibaura Institute of Technology, Japan, along with Dr. Makoto Ohmoto from the Takasaki University of Health and Welfare, Japan, Dr. Yasuyuki Fujii and Dr. Takafumi Shimizu from Shibaura Institute of Technology, Japan, and Dr. Keiko Abe from University of Tokyo, Japan, and Dr. Vittorio Calabrese from University of Catania, Italy, conducted a review to understand the interaction between the polyphenols and T2R and the resulting health benefits. Their findings were published on 18 June 2024 in the journal of Food Bioscience. 

Professor Osakabe asserts, “Despite their poor absorption, there are reports that polyphenols improve glucose tolerance. We are investigating the relationship between polyphenol intake and the risk of type II diabetes, as the mechanism of this beneficial effect is still unknown.” 

The review highlights the mechanism of communication between the polyphenols, T2Rs, and the brain centers regulating glucose homeostasis and appetite. Polyphenol-mediated binding and activation of T2R in the GI tract promotes secretion of GI hormones such as cholecystokinin (CCK) and incretins. The incretins include the glucose-dependent insulinotropic polypeptide and glucagon-like peptide-1 (GLP-1) that trigger insulin secretion and regulate blood glucose homeostasis. CCK and GLP-1 regulate appetite and food intake by influencing GI motility. Together, the GI hormones triggered by polyphenols reduce the risk of obesity and diabetes. 

Prof Osakabe explains, “The GI hormones are known to regulate feeding behavior and maintain glucose tolerance via the endocrine and nervous systems, thus it is possible that the bitterness of polyphenols helps to reduce the risk of diabetes and its complications, through T2R activation.” 

Overall, the findings suggest that ingested polyphenols, despite remaining unabsorbed, promote the secretion of gastrointestinal hormones by activating bitter taste receptors expressed on the digestive secretory cells, thereby regulating blood sugar levels and appetite. Prof. Osakabe concludes, “Our study highlights the importance of consumption of polyphenols to reduce obesity and diabetes risk through regulation of blood sugar levels and appetite.”

 

---

Reference

Title of original paper:	Gastrointestinal Hormone-Mediated Beneficial Bioactivities of Bitter Polyphenols
Journal:	Food Bioscience
Article link:	10.1016/j.fbio.2024.104550

Authors

About Professor Naomi Osakabe from SIT, Japan

Dr. Naomi Osakabe is a Professor at the Department of Bioscience and Engineering at Shibaura Institute of Technology (SIT), Japan. She is also affiliated with the Functional Control Systems and Systems Engineering and Science sections of the Graduate School of Engineering and Science, SIT. Her research interests include agriculture and food science, polyphenols, taste receptors, redox and nutrition. With over 30 years of experience and more than 150 publications, Professor Osakabe is an expert in Food and Nutrition and serves on the editorial boards of leading scientific journals.

Funding Information

This work was supported by JSPS KAKENHI (Grant Number 23H02166).