Mulberry leaves plus water chestnut tea lowers blood glucose in borderline diabetes

Individuals with borderline diabetes may benefit from drinking mulberry leaves and water chestnut husk (MW) tea, which has been shown in a Japan study to reduce insulin secretion and prevent spikes in blood glucose levels.

“MW tea has both hypoglycaemic and antioxidant properties, thus expected to be an effective food for borderline diabetics to prevent a rapid rise in blood glucose levels without a large increase in insulin levels,” the investigators said.

In this randomized, double-blind, placebo-controlled crossover comparison study, the investigators developed an MW tea and examined its effect on postprandial blood glucose levels in 30 participants with borderline diabetes. They measured the polyphenols and 1-deoxynojirimycin contents as well as the antioxidant activity of MW tea in an in vitro experiment.

The tea (test food, 3 g) contained 10.2 mg of 1-deoxynogirimycin and 61.3 mg of total polyphenols, exhibiting higher antioxidant activity than the placebo foods. [Asia Pac J Clin Nutr 2025;34:174-182]

Blood glucose levels in the test food group decreased substantially 30 and 60 min after rice consumption compared with those in the placebo group. Insulin levels were also significantly lower at 30, 60, 90, and 120 min after eating rice.

“The MW tea was found to suppress insulin secretion, while reducing the increase in postprandial blood glucose levels,” the investigators said.

Suppression

Several studies have reported the effects of mulberry leaves on blood glucose suppression. For instance, a report by Kimura and colleagues showed a significant difference in blood glucose and insulin levels 60 min after ingesting 12 mg of 1-deoxynogirimycin and sugar relative to placebo. [J Agric Food Chem 2007;55:5869-5874; J Diabetes Investig 2011;2:318-323; Nutr Metab (Lond) 2021;18:41]

In the current study, blood glucose levels decreased after consuming MW tea followed by cooked rice compared with placebo tea. Insulin levels also significantly dropped at all time points.

“These findings suggest that mulberry leaves combined with water chestnut husk are more effective in controlling blood glucose and insulin levels than mulberry leaves alone,” the investigators said.

Mechanism

The suppression of postprandial blood glucose elevation and insulin secretion by MW tea is potentially driven by the α-glucosidase inhibitory activity of 1-deoxynogirimycin found in mulberry leaves and polyphenols found in water chestnut husk. [Carbohydr Res 1994;259:243-255; Food Chem 2014;165:42-49; Food Preserv Sci 2004;30:223-229]

“However, since 95 percent of the test foods used in this study consisted of mulberry leaves, the effect of 1-deoxynogirimycin appears to be the primary contributor,” according to the investigators. “[I]ngestion of 10.2 mg of 1-deoxynogirimycin significantly reduced the increase in postprandial blood glucose levels and insulin secretion.”

In addition, the body absorbs 1-deoxynogirimycin from the gastrointestinal tract and distributes it in organs, including the kidneys, to control blood glucose. [J Nutr Sci Vitaminol (Tokyo) 2019;65:157-163]

“Type 2 diabetes, caused by a poor lifestyle, such as overeating, unbalanced diets, lack of exercise, and excessive stress, is a serious concern,” the investigators said. “Prevention of diabetes is crucial as it can reduce the quality of life and even lead to fatal complications.”