The researchers studied the effect of regular table grapes (a blend of green, red, and black grapes) that were mixed into the rat diet in a powdered form, as part of either a high- or low-salt diet. They performed many comparisons between the rats consuming the test diet and the control rats receiving no grape powder — including some that received a mild dose of a common blood-pressure drug. All the rats were from a research breed that develops high blood pressure when fed a salty diet.
In all, after 18 weeks, the rats that received the grape-enriched diet powder had lower blood pressure, better heart function, reduced inflammation throughout their bodies, and fewer signs of heart muscle damage than the rats that ate the same salty diet but didn't receive grapes. The rats that received the blood-pressure medicine, hydrazine, along with a salty diet also had lower blood pressure, but their hearts were not protected from damage as they were in the grape-fed group.
Says Mitchell Seymour, M.S., who led the research as part of his doctoral work in nutrition science at Michigan State University, "These findings support our theory that something within the grapes themselves has a direct impact on cardiovascular risk, beyond the simple blood pressure-lowering impact that we already know can come from a diet rich in fruits and vegetables." Seymour manages the U-M Cardioprotection Research Laboratory, which is headed by U-M heart surgeon Steven Bolling, M.D.
The researchers think flavanoids in grapes might be providing the heart protection.
"Although there are many natural compounds in the grape powder itself that may have an effect, the things that we think are having an effect against the hypertension may be the flavanoids – either by direct antioxidant effects, by indirect effects on cell function, or both. These flavanoids are rich in all parts of the grape - skin, flesh and seed, all of which were in our powder." Bolling explains.
You can get flavanoids from berries and cherries as well. The amount of grapes used is equivalent to a human eating 9 servings of grapes per day.
He notes that the popular DASH diet, which is low in salt and high in fruits and vegetables, has been proven to reduce mild high blood pressure without medication. The dose of whole table grape powder that was consumed in the study was roughly equivalent to a person eating nine human-sized servings of grapes a day. Currently, five to nine servings of fruits and vegetables are recommended as part of the DASH diet.
Other measures of heart function were better in the grape-fed group.
The researchers also measured the distortion of the heart size, weight and function that occurred over time – characteristics of heart failure – and found that the high-salt grape group had less of a change than the high-salt hydrazine group. Parameters related to the diastolic blood pressure – an important factor in human heart failure — and to the heart's relaxation during the diastolic phase also changed in just the high-salt grape group. Finally, the grape-fed rats had improved cardiac output, or more blood pumped per unit of time.
The researchers also looked for signs of inflammation, oxidative damage and other molecular indicators of cardiac stress. Again, the rats that received the high-salt grape diet had lower levels of these markers than rats that received the high-salt diet with hydrazine – and even the low-salt grape-eating rats had lower levels than the rats that received a low-salt diet alone.
Eat more fruits and vegetables or die before your time.
Update: A recent survey of grape health benefit research finds grapes provide health benefit in humans too.
So far, most of the evidence on grape polyphenols comes from laboratory experiments and animal studies. However, a few studies support the disease-preventing benefits of grapes in humans. Studies in patients treated with grape seed extracts have shown improvements in blood flow and cholesterol levels. In other studies, drinking Concord grape juice has improved measures of blood flow in patients with coronary artery disease and lowered blood pressure in patients with hypertension.
|Share |||Randall Parker, 2008 October 31 05:30 AM Aging Diet Heart Studies|