MACRO- AND MICRONUTRIENT MODULATION OF BIOMARKERS OF CHRONIC DISEASE AND INDICATORS OF NUTRITIONAL ADEQUACY
Location: Food Components and Health Laboratory
Title: Oolong tea does not improve glucose metabolism in non-diabetic adults
Submitted to: European Journal of Clinical Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 27, 2010
Publication Date: October 20, 2010
Citation: Baer, D.J., Novotny Dura, J., Harris, K., Stote, K., Clevidence, B.A., Rumpler, W.V. 2010. Oolong tea does not improve glucose metabolism in non-diabetic adults. European Journal of Clinical Nutrition. 65:87-93.
Interpretive Summary: Diabetes, a condition that affects 246 million people worldwide, leads to a number of secondary problems, including kidney failure, vision loss, cardiovascular disease, and stroke. Diabetes is primarily characterized by the body’s inability to appropriately metabolize glucose, the main form of circulating sugar used for energy. Survey studies suggest that one lifestyle strategy that may improve sugar metabolism is consumption of plant-based compounds called polyphenols. Tea, the most widely consumed beverage in the world next to water, is particularly high in polyphenols. The evidence surrounding the potential for tea to influence diabetes has been controversial, in part because previous research studies were not highly controlled and tea beverages were not well characterized. Therefore, we conducted a nutrition study in which volunteers consumed oolong tea or oolong tea enriched with polyphenols as part of their normal diet, then tested the body’s ability to metabolize glucose. Neither oolong tea nor the enriched oolong tea improved glucose metabolism in non-diabetic adult volunteers based on this highly controlled dietary intervention trial.
Studies of the influence of tea on glucose metabolism have produced inconsistent results, possibly due to lack of dietary control and/or unclear characterization of tea products. Therefore, a double-blind crossover study was conducted in which healthy males (n=19) consumed each of three oolong tea products or a control beverage as part of a controlled diet. Treatment beverages (1.4L/d) were consumed for 5 d, followed by assessment of fasting plasma glucose, fasting serum insulin, and an oral glucose tolerance test. Tea products included oolong tea, oolong tea with added catechins, and oolong tea with added oolong tea polyphenols, and control beverages included caffeinated water and unsupplemented water. On the fifth day of each treatment period, treatment beverages were consumed with a standardized meal, and glucose and insulin responses were assessed for 240 m. No significant differences were detected for fasting plasma glucose, fasting serum insulin, incremental plasma glucose area under the concentration time curve (AUC), total plasma glucose AUC, or total serum insulin AUC. In conclusion, neither oolong tea, nor oolong tea supplemented with catechins or other polyphenols, produced improved glucose metabolism in healthy adult volunteers based on this highly controlled dietary intervention trial.