Banaba (Lagerstroemia speciosa) is a plant native to India, Southeast Asia and the Philippines and has several medicinal uses. In many cultures the banaba leaf is brewed into a tea and used as a treatment for diabetes and as a weigh loss aid. Banaba Leaf Extract provides a blood sugar lowering effect similar to that of insulin in that it induces glucose transport from the blood into body cells.

Recently, researchers have isolated an active ingredient in the banaba leaf called corosolic acid which was originally thought to be "the" blood sugar regulating substance in the leaf. Other researchers have found that corosolic acid may not be the only active ingredient in banaba leaves. A study published in the journal Planta Medica in 2001 compared a whole-leaf extract of banaba with insulin in cell cultures. The researchers concluded that the whole herb has a glucose lowering effect. Another study reported that banaba leaf extract contains at least three active ingredients that affect blood sugar.

Banaba Leaf extract has been studied on diabetic mice and has been shown to help improve control over blood sugar levels. It is thought to be safe and effective for reducing elevated blood sugar levels. In a recent human study, subjects using the softgel form of a corosolic acid preparation each day for two weeks experienced a 30 percent drop in blood sugar levels. Subjects taking the capsule had a 20 percent drop. Researchers considered both levels of blood sugar reduction significant.

In a prior study, some of the same researchers observed that individuals receiving the oil-based corosolic acid softgel formula also had an increased tendency toward weight loss--an average of about 3.2 pounds.