Grapes Shown To Protect Against Diabetes

Consuming grapes protected against the destruction of insulin-producing cells (known as beta cells) in the pancreas, significantly reducing the incidence of diabetes in lab rodents.

Naturally occurring antioxidants in grapes known as polyphenols are believed to be responsible for this beneficial impact.

The results of this study showed that grapes reduced the infiltration of immune cells into the islets of Langerhans, the specific area of the pancreas where the insulin-producing beta cells reside, thus preventing their damaging effects on the beta cells. Grapes also reduced the levels of an inflammatory protein in spleen cells, known as TNF-alpha.

Additionally, the researchers observed that the grape diet resulted in a significantly higher antioxidant capacity of the blood. Higher blood antioxidant capacity may potentially contribute to a reduction in oxidative stress in the islets of Langerhans and form yet another layer of protection; however, this was not directly tested. The powerful antioxidant activity of grape polyphenols is thought to be part of the mechanism of protection attributed to grapes.

"The protective effect of grapes was quite significant and very exciting," said principal investigator Susan J. Zunino, Ph.D. of the USDA Agricultural Research Service's Western Human Nutrition Research Center in Davis, California where the study was conducted. "In this study we observed firsthand their effect on two of three critical components for the prevention of type I diabetes: the preservation of the beta cells and the inhibition of inflammation. Other studies have shown that quercetin and anthocyanins, which are phytonutrients present in grapes, enhanced insulin secretion and sensitivity, which is the third critical component. Clearly more studies need to be done to fully define the mechanisms of action for the grapes and their potential as a dietary intervention for diabetes."

Leading health experts agree that to get the benefit of phytonutrients found in foods, such as the polyphenols in grapes, it is best to consume the whole fruit as opposed to a supplement. Fresh grapes provide an array of natural antioxidant compounds including polyphenols, such as resveratrol, and other biologically active compounds in their natural environment, all of which may either contribute to the beneficial effects or provide the optimal conditions for a certain phytonutrient to exert its particular individual benefit.

"This study further reinforces the growing evidence that grapes have anti- inflammatory and antioxidant properties that appear to offer significant health benefits across a number of disease states," said Kathleen Nave, president of the California Table Grape Commission.

In order to ensure the scientific validity of grape health studies, a representative sample of fresh California grapes was collected and freeze- dried into an edible grape powder which contains all of the biologically active compounds found in fresh grapes.

The onset of Type 1 diabetes, also known as insulin dependent diabetes mellitus (IDDM) is characterized by the infiltration of activated T lymphocytes in to an area of the pancreas known as the islets of Langerhans. This causes inflammation and the progressive destruction of the body's only insulin-producing cells, the beta cells. The destruction of these cells leads to a severe depletion of insulin, which is critical to the body's metabolism. To survive, insulin must be delivered via injection or pump. Type I diabetes accounts for 5-10% of all diagnosed human cases of diabetes, according to the American Diabetes Association.

This study was supported by the United States Department of Agriculture and the National Institutes of Health.