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Oolong tea does not improve glucose metabolism in non-diabetic adults.

  • 2010-10-20
  • European journal of clinical nutrition 65(1)
    • D J Baer
    • J A Novotny
    • G K Harris
    • K Stote
    • B Clevidence
    • W V Rumpler

Study Design

Type
Randomized Controlled Trial (RCT)
Sample size
n = 19
Population
19 healthy males
Methods
Double-blind crossover study, 5 days of 1.4 L/day of oolong tea or control beverage in a controlled diet
Blinding
Double-blind
Duration
5 days
Funding
Unclear
  • Rigorous Journal

Background

Studies of the influence of tea on glucose metabolism have produced inconsistent results, possibly because of the lack of dietary control and/or unclear characterization of tea products.

Methods

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 (1.4 l/day) were consumed for 5 days, 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 min.

Results

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.

Conclusions

Neither oolong tea nor oolong tea supplemented with catechins or other polyphenols produced improved glucose metabolism in healthy adult volunteers on the basis of this highly controlled dietary intervention trial.

Research Insights

  • Oolong Tea→Increased Blood Glucose Levels

    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.

    Effect
    Neutral
    Effect size
    Small
    Dose
    1.4 L/day
  • Oolong Tea→Reduced Fasting Glucose

    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.

    Effect
    Neutral
    Effect size
    Small
    Dose
    1.4 L/day
  • Oolong Tea→Reduced Glucose Level

    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.

    Effect
    Neutral
    Effect size
    Small
    Dose
    1.4 L/day
  • Oolong Tea→Reduced Insulin AUC

    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.

    Effect
    Neutral
    Effect size
    Small
    Dose
    1.4 L/day
  • Oolong Tea→Reduced Insulin Levels

    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.

    Effect
    Neutral
    Effect size
    Small
    Dose
    1.4 L/day
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