Eating grapes has been found to lower blood pressure, improve heart function and reduce other risk factors for heart disease and metabolic syndrome, a new study claims. American researchers found this could be due to the phytochemicals - naturally occurring antioxidants - that grapes contain.

Following animal tests, the research revealed that a grape-enriched diet prevented risk factors for metabolic syndrome, a condition which is a precursor to type-2 diabetes.

Researchers studied the effect of regular table grapes (a blend of green, red and black grapes) that were mixed into a powdered form and integrated into the diets of laboratory rats as part of a high-fat, American style diet. All of the rats used were from a research breed that is prone to being overweight.

They performed many comparisons between the rats consuming a grape-enriched diet and the control rats receiving no grape powder. Researchers added calories and sugars to the control group to balance the extra calories and sugars gained from getting the grape powder.

After three months, the rats that received the grape-enriched diet had lower blood pressure, better heart function, and reduced indicators of inflammation in the heart and the blood than rats who received no grape powder. Rats also had lower triglycerides and improved glucose tolerance.

The effects were seen even though the grape-fed animals had no change in body weight. In all, researchers say the study demonstrates that a grape-enriched diet can have broad effects on the development of heart disease and metabolic syndrome and the risk factors that go along with it.

"The possible reasoning behind the lessening of metabolic syndrome is that the phytochemicals were active in protecting the heart cells from the damaging effects of metabolic syndrome. In the rats, inflammation of the heart and heart function was maintained far better," said one of the researchers.

The researchers also looked for signs of inflammation, oxidative damage and other molecular indicators of cardiac stress. Again, the rats who consumed the grape powder had lower levels of these markers than rats who did not receive grapes.

Metabolic syndrome is usually characterized by factors such as excess belly fat; high triglycerides which can lead to plague build-up in the artery walls; high blood pressure; reduced glucose tolerance; and elevated c-reactive protein, a marker for inflammation in the body.

Those with metabolic syndrome are at higher risk for cardiovascular disease and type-2 diabetes.

This study suggests that it may be possible that grape consumption can change the downhill sequence that leads to heart disease by prolonging the time between when symptoms begin to occur and a time of diagnosis.

"Reducing these risk factors may delay the onset of diabetes or heart disease, or lessen the severity of the diseases," said the lead researcher. "Ultimately it may lessen the health burden of these increasingly common conditions."