The Durk Pearson & Sandy Shaw®
Life Extension NewsTM
Volume 13 No. 3 • June 2010

Weight Control, Diabetes Inhibition of Starch Digestion by Black Tea

A 2010 paper1 reports on a comparison of green (nonfermented), oolong (semifermented), and black (fully fermented) teas on their ability to inhibit human salivary alpha-amylase (HSA) and mammalian alpha-glucosidase (AGH), two enzymes that digest starch, with the alpha-glucosidase in the small intestine completing the process to produce glucose that is actively transported into the bloodstream. The fully fermented black tea was most effective at inhibiting HSA and AGH, with IC50 (concentration required to inhibit 50% of the enzymatic activity) reported to be 0.42 to 0.67 and 0.56 to 0.58 mg of tea leaves/mL, respectively. The use of alpha-amylase and alpha-glucosidase inhibitors has been shown to be beneficial in the treatment of type 2 diabetes.1 This is essentially a way to produce a low glycemic index (GI) meal from a higher GI meal containing starch.

The paper1 also reports other natural inhibitors of alpha-amylase and alpha-glucosidase that include cumin seeds, mulberry leaves, and mangosteen pericarp. However, tea is particularly useful as it is easy to incorporate into a daily regimen that includes frequent servings.

In this study, the effects of the teas on the two enzymes was investigated using real food (rice noodles — the scientists who performed this study were located in Singapore, so they chose a popular starchy Asian food) in a simulated digestion experiment. One of the black teas (LB) was reported to reduce rice noodle digestion by 28% (30 mg of tea leaves/mL).

As the authors explain, “[b]lack tea may be inferior to acarbose [a drug that inhibits the two enzymes] in terms of delaying starch digestion. However, treatment with the latter often leads to adverse health effects (such as flatulence, diarrhea and abdominal pain) among diabetic patients.”1 The adverse effects are caused by microbial digestion of the undigested starch that reaches the large intestine. Additional experiments by the authors1 found that theaflavins (found in black but not green teas) were far more potent in inhibiting HSA and AGH than catechins (plentiful in green but not black teas).

  1. Koh et al. Evaluation of different teas against starch digestibility by mammalian glycosidases. J Agric Food Chem 58(1):148-54 (2010).

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