Black tea decreases postprandial blood glucose levels in healthy humans and contains high-molecular-weight polyphenols that inhibit α-glucosidase and α-amylase in vitro: a randomized, double blind, placebo-controlled, crossover trial | Functional Foods in Health and Disease - Online ISSN: 2160-3855; Print ISSN: 2378-7007 Skip to main content Skip to main navigation menu Skip to site footer Open Menu Functional Foods in Health and Disease - Online ISSN: 2160-3855; Print ISSN: 2378-7007 Home Food Science Publisher Functional Food Center Current Archives About About the Journal Aims and Scope Contact Editing Services Editorial Team Express Peer Review Graphical Abstract Journal Insights Privacy Statement Submissions Announcements Search Search Register Login Home / Archives / Vol. 11 No. 5 (2021): May 2021 / Research Articles Black tea decreases postprandial blood glucose levels in healthy humans and contains high-molecular-weight polyphenols that inhibit α-glucosidase and α-amylase in vitro: a randomized, double blind, placebo-controlled, crossover trial Authors Yoshikazu Isono Biwako Research Institute, Otsuka Foods Co., Ltd. https://orcid.org/0000-0003-1031-2887 Hisako Watanabe Biwako Research Institute, Otsuka Foods Co., Ltd. Masafumi Kumada Biwako Research Institute, Otsuka Foods Co., Ltd. Tsuyoshi Takara Medical Corporation Seishinkai, Takara Clinic Shin-ichiro Iio ORTHOMEDICO Inc DOI: https://doi.org/10.31989/ffhd.v11i5.791 Abstract Background: To prevent diabetes, it is important to control postprandial glycemic levels. Studies have suggested that consuming black tea decreases the risk of type 2 diabetes; however, only a few studies have examined the effects of black tea on postprandial glycemic control after consuming starch-rich foods. In addition, the mechanism underlying the suppression of postprandial glucose levels remains unclear. Objective: To investigate the effects of black tea on postprandial blood glucose levels in healthy humans and to identify the components of black tea that inhibit digestive enzymes. Methods: The inhibitory activity of black tea on digestive enzymes was measured, and the inhibitory components were fractionated. Healthy Japanese adults ingested 200 ml of black tea, and its effect on postprandial blood glucose and insulin levels were investigated.  Results: Black tea dose-dependently inhibited α-glucosidase, sucrase, and α-amylase activity. The major components responsible for this inhibition were high–molecular-weight polyphenols. The galloyl moieties present in these compounds play an important role in their inhibitory activities. Two randomized, double-blind, placebo-controlled, crossover studies of healthy human subjects (total n = 46) were conducted to investigate the effect of black tea on blood glucose and insulin levels. Combined data from the two studies showed that black tea ingestion (200 mL) after cooked rice intake (200 g) significantly reduced the incremental area under the curve of glucose (P =.024) and insulin (P =.014) compared to placebo drink. Conclusions: The high–molecular-weight polyphenols in black tea inhibited α-glucosidase, sucrase, and α-amylase activity in a dose-dependent manner. Furthermore, black tea ingestion after eating cooked rice significantly reduced the incremental area under the curve of glucose and insulin. These effects of black tea could be attributed to the inhibition of digestive enzymes by high–molecular-weight polyphenols containing galloyl groups. Keywords: black tea, blood glucose, α-glucosidase, α-amylase, polyphenol Author Biographies Yoshikazu Isono, Biwako Research Institute, Otsuka Foods Co., Ltd. Senior Researcher Hisako Watanabe, Biwako Research Institute, Otsuka Foods Co., Ltd. Researcher Masafumi Kumada, Biwako Research Institute, Otsuka Foods Co., Ltd. chief of the chemical lab. Tsuyoshi Takara, Medical Corporation Seishinkai, Takara Clinic physician Shin-ichiro Iio, ORTHOMEDICO Inc section chief Downloads [Abstract] [Full Article] Published 2021-05-12 Issue Vol. 11 No. 5 (2021): May 2021 Section Research Articles License Authors retain the copyright of their articles and grant the Functional Food Center (FFC) and its journals the right of first publication under the terms of the Creative Commons Attribution 4.0 International License. This license permits unrestricted use, distribution, and reproduction in any medium, including commercial use, provided the original author(s) and source are properly credited. Authors may post and share their published work freely, provided that the original publication in this journal is acknowledged. By submitting to this journal, authors confirm that their manuscripts are original, not under consideration elsewhere, and that they hold the necessary rights to grant this license. The Functional Food Center encourages open scientific exchange and allows derivative and extended works, provided attribution to the original publication is maintained. About the Journal      Editing Services      Graphical Abstract      Journal Insights        Submissions        Editorial Team       Privacy Statement        Contact        Current        Archives   Open Journal Systems Hosting and Support by: OpenJournalSystems.com