The most positive research has come from studies into a plant native to India, Gymnema sylvestre. The leaves of this plant have been used to treat diabetes for over 2000 years and has been relatively widely studied since the 1930s.
In one study, a water soluble extract of Gymnema leaf was given to 27 type I diabetics at a dose of 400 mg/day for 10-12 months. During the study, their insulin requirements were decreased by about half, and their average blood glucose was reduced from 232 to 152 mg/ dL. Cholesterol, triglycerides and amylase (an enzyme that breaks down sugar) were also significantly lowered. In contrast, in study patients taking insulin therapy alone, these and other biochemical markers remained high (J Ethnopharmacol, 1990; 30: 281-94).
In two animal studies, Gymnema extract doubled the number of islet and beta cells in the pancreas of diabetic rats, lending support to the theory that it increases insulin secretion by regenerating beta cells (J Ethnopharmacol, 1986; 18: 143-6). But, as encouraging as these results are, remember that animal research often doesn't apply to humans.
Some animal studies found Gymnema to be effective in lowering blood glucose only in mild to moderate diabetes where there is still some beta cell activity. However, in one study, treatment with Gymnema in rats with severe diabetes significantly prolonged life (Isr J Med Sci, 1985; 21: 540-2).
So impressive have the initial studies with Gymnema been that a US company, PharmaTerra, has put their full backing behind a remedy made from the plant ProBeta. ProBeta comes in 250-mg tablet, and has been on the market since 1998. It differs from other Gymnema products in that it is not standardised for gymnemic acid.
'Gymnemic acid' is not a single acid, but a blanket name for a series of chemicals found in the leaves of the plant. While the plant contains chemicals that are known to retard glucose absorption across the small intestine, it also contains other chemicals that may inhibit the absorption of other nutrients as well and may also limit the regeneration of the pancreas. ProBeta, claims its manufacturer, has been formulated to overcome any potential adverse effects of gymnemic acid.
Other promising botanical research has focused on Momordica charantia (bitter melon, bitter gourd) commonly found in China, India and Africa, where it has a history of medicinal use. It contains many active ingredients (Uppsala J Med Sci, 1977; 82: 39-41) and is structurally and pharmacologically comparable to bovine insulin (J Nat Med, 1993; 4: 16-21)
When one of Momordica's active ingredients, p-insulin, was given to nine diabetic patients, researchers found an onset of action similar to bovine insulin (30-60 min) and a peak hypoglycaemic effect after four hours in type I diabetics, compared with two to three hours with regular insulin (Uppsala J Med Sci, 1977; 82: 39-41).
The hypoglycaemic effects of this plant appear to be, in part, due to extrapancreatic activity, including increased glucose utilisation by the liver, decreased glucose synthesis by depression of key gluconeogenic enzymes and enhanced glucose oxidation.
Several animal studies have confirmed the blood sugar lowering effects of Momordica extracts (Pharmacol Res, 1996; 33: 1-4; Biochem J, 1993; 292: 267- 70) while others have not (Plants Med, 1990; 56: 426-9). One recent study found that, like Gymnema, bitter melon was able to regenerate beta cells in diabetic rats (Diabetes Res Clin Pract, 1998; 40: 145-51). Again, remember this may not apply to humans.