To demonstrate this, the team led by Fr?İd?İric Calon used a type of transgenic mice that produce two proteins found in the brains of Alzheimer patients-tau proteins, which prevent proper neuron functioning, and amyloid-beta, associated with the formation of senile plaques within the brains of afflicted patients.
The researchers fed transgenic and regular mice different diets for nine months, after which they compared the effects on the animals' brains.
The mice whose diet was poor in omega-3s and rich in fat (60% of consumed calories) showed amyloid-beta and tau protein concentrations respectively 8.7 and 1.5 times higher than the control group mice, whose food contained 7 times less fat. The high-fat diet also reduced drebrin protein levels in the brain, another characteristic of Alzheimer's disease.
"Metabolic changes induced by such a diet could affect the inflammatory response in the brain," suggests study co-author Carl Julien to explain the link between fat consumption and Alzheimer's.
In most Western countries, diets rich in saturated fats and poor in omega-3s are the norm. "Our findings lead us to believe that a diet containing more omega-3s and less saturated fat could prevent the development of Alzheimer's, at the very least among people genetically predisposed to the disease," comments Dr. Calon. "We cannot state with any certainty that what we have observed among transgenic mice also occurs in humans, but there is no harm in eating less fat and more omega-3s," concludes the researcher.
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The rats in the study were from a strain called Dahl rats, which have been specially bred to all be susceptible to salt-induced hypertension. This allowed the researchers to look at a uniform sample of rats that would be affected in the same way by their diet, so that the effects of the salt level, grape powder and hydrazine could be seen clearly.
Each group of 12 rats was fed the same weight of food each day, with powdered grapes making up 3 percent of the diet (by weight) for rats that received grapes as part of either a low-salt or high-salt diet. The rats that received hydrazine were fed it through their water supply in a dose that has been previously shown to be effective in reducing blood pressure.
The rats in the high-salt grape and high-salt hydrazine groups did develop high blood pressure over time, but they had lower systolic blood pressures than the high-salt rats that did not receive grapes.
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.
In all, the researchers say, the study demonstrates that a grape-enriched diet can have broad effects on the development of hypertension and the risk factors that go along with it. Whether the effect can be replicated in humans, they say, remains to be seen.
Reference: Journal of Gerontology: Biological Sciences, 2008, Vol. 63A, No. 10, October 2008
For more information on the DASH diet, which has already been shown to lower blood pressure in people, visit nhlbi.nih/health.
For information on the U-M Cardioprotection Research Laboratory, visit sitemaker.umich/cardiac.phytomed/research.
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