The antidiabetic effect of banaba leaves is one reason why they’re popular.
Researchers attribute this effect to several compounds, namely corosolic acid, ellagitannins, and gallotannins.
Corosolic acid lowers blood sugar levels by increasing insulin sensitivity, enhancing glucose uptake, and inhibiting alpha-glucosidase — an enzyme that helps digest carbs. That’s why it’s claimed to have an insulin-like effect.
Insulin is the hormone that regulates blood sugar levels. In people with type 2 diabetes, insulin resistance increases the demand for this hormone. However, the pancreas may not be able to meet those demands, resulting in high blood sugar levels.
In one study in 31 adults, those who received a capsule containing 10 mg of corosolic acid had lower blood sugar levels for 1–2 hours after performing an oral glucose tolerance test, compared with those in a control group.
In addition to corosolic acid, ellagitannins — namely lagerstroemin, flosin B, and reginin A — also improve blood sugar levels.
They promote glucose uptake by activating glucose transporter type 4 (GLUT4), a protein that transports glucose from the bloodstream into muscle and fat cells.
Likewise, gallotanins seem to stimulate the transportation of glucose into cells. It’s even hypothesized that a type of gallotanin called penta-O-galloyl-glucopyranose (PGG) has higher stimulatory activity than corosolic acid and ellagitannins.
While studies have found promising results on the anti-diabetic properties of banaba leaves, most have used a combination of herbs or compounds. Thus, further studies on the leaves alone are needed to better understand their blood sugar-lowering effects.