An isolate from the leaves of Gymnema sylvestre, having a specified molecular weight, is useful for the treatment of diabetes. The isolate has a molecular weight at least about 3000 Daltons as determined by molecular weight cut-off filtration. Glucose metabolism in a human patient is regulated by dosage forms that contain the aforesaid isolate from the leaves of Gymnema sylvestre, optionally in combination with a non-metabolizable polysaccharide such as the exudate of Sterculia urens.