Mulberry leaf extracts have a history of use for blood sugar management, with the extracts being used to treat diabetes in some Asian countries​.

The benefits of the extracts are linked to a compound called 1-deoxynojirimycin (DNJ) and some of its derivatives, which are reported to inhibit the activity of a carbohydrate digesting enzyme called alpha-glucosidase. By slowing or stopping this enzyme, the digestion of starch and oligosaccharides is slowed, which suppresses blood glucose spikes after eating.

Writing in the Journal of Functional Foods​, ​Korean researchers from Ewha Woman’s University and the Seoul National University of Science and Technology noted that intakes of 2.5 or 5 grams of mulberry leaf led to lower blood glucose levels after a ingesting a maltose solution.

“Ingestion of mulberry leaf aqueous extract containing 0.36% DNJ effectively reduced hyperglycemia after a 75 g maltose challenge in healthy subjects from the initial measurement at 0–180 min,”​ wrote the researchers.

“The effective doses were 2.5–5 g of mulberry leaf aqueous extract, which correspond to 9–18 mg of DNJ, respectively.”​

Study details​

The Seoul-based researchers recruited 50 healthy people to participate in their randomized, double-blind, placebo-controlled trial. Subjects were randomly assigned to one of five groups: Four groups received a maltose powder drink with 0, 1.25, 2.5, or 5 grams of the mulberry leaf extract. The fifth group consumed a beverage with 5 grams of the mulberry leaf extract 30 minutes before drinking the maltose solution.

Results showed that the 2.5 and 5 gram mulberry doses were associated with lower glucose levels in the healthy subjects, and there were no significant differences between the two doses.

In addition, no differences between the pre- and simultaneous administration of mulberry leaf extract groups were recorded.

Whole extract ​

The Korean researchers said that, according to a previous study by their group, the blood sugar lowering effects are only observed when whole mulberry leaf extract is used, and are not observed when DNJ is administered on its own.

“As mulberry leaf may contain dietary fibers, which are unabsorbable substances, it is reasonable to assume that they may act on the rate of gastric emptying and intestinal absorption,”​ they said. “Besides DNJ and soluble dietary fiber, flavonoids and related constituents found in mulberry leaf were also described for inhibiting glucose uptake as well as alpha-glucosidase acitivity.​

“These flavonoids were reported chlorogenic acid, rutin and quercetin. Therefore, the lowering of the postprandial glucose response after loading with maltose might be attributed to the additive effect of inhibiting maltase and glucose absorption; however, we did not compare DNJ alone to mulberry extract in this study.”​

Source: Journal of Functional Foods​​

Volume 5, Issue 3, Pages 1502–1506, doi: 10.1016/j.jff.2013.04.015

“Acute intake of mulberry leaf aqueous extract affects postprandial glucose response after maltose loading: Randomized double-blind placebo-controlled pilot study”​

Authors: H.I. Chung, J. Kim, J.Y. Kim, O. Kwon