A study in mice suggests a lower-calorie diet can help trigger the production of a protein that protects the brain from the disease, said researchers at the Mount Sinai School of Medicine in New York City.

In the study, the mice in one group were permitted to eat as they wished, while the other group of mice was fed only 70 percent of that amount.

When the animals were killed six months later, researchers discovered the brains of the calorie-restricted mice held significantly higher levels of an anti-aging protein, SIRT1, the researchers reported in the July issue of the Journal of Biological Chemistry.

That protein has been shown to curtail and reverse the production of plaque in the brain, a typical symptom of Alzheimer's disease. Researchers have found the protein can also enhance the function of a patient's metabolism, kidneys and liver.

"The real message is that, in an animal model of Alzheimer's disease, caloric restriction led to the elevation of molecules that are associated with longevity and good health," said Dr Giulio Pasinetti, a professor of psychiatry and neuroscience who led the study.

"This may be the reason why caloric restriction may work to prevent Alzheimer's disease."

According to the National Institute of Aging, about 4.5 million Americans are living with Alzheimer's disease, the most common cause of elderly dementia.

Its first symptom is often a mild forgetfulness that escalates into an inability to care for oneself and, eventually, death. There is no cure, and treatments merely delay the progression of the disease for a short time.