Older people might be able to preserve their brain power for longer if they ate less, a study suggests.
Extreme low-calorie diets may not be practical
Rats fed diets with 40% fewer calories produced double the levels of a protein known to protect brain cells.
Brain cells, or neurons, are unusual among the majority of body tissues in that they have very limited abilities to regenerative - once they are gone, they do not tend to come back.
Doctors are searching for ways to slow down the death of brain cells, and perhaps unlock a way to tackle diseases such as Alzheimer's and Parkinson's - both of which are characterised by the death of excessive numbers of neurons.
Extreme calorie-limited diets have already been shown to be the only way to extend the lifespan of healthy animals.
Previous studies have suggested that calorie restriction increased the mental capacity of several species.
The latest study, by researchers at the University of Florida, looked specifically at the effects of these diets on brain cells.
Some older rats in their experiment were given an unrestricted diet - but others were given 40% less food, even though their diet was more "nutritionally dense" to compensate.
Samples taken from regions of the brain important in learning and memory were tested.
The researchers found that levels of a protein called cytochrome c increased with age in the normally-fed rats.
This protein is part of a natural "clean-up" process that kills cells which have become damaged.
In the calorie-restricted animals, however, the protein levels did not increase.
The researchers also looked at another protein, called ARC, which plays a role in preventing the release of cytochrome C.
In theory, higher levels of ARC could mean that brain cells were less likely to be destroyed.
In the calorie-restricted rats, levels of ARC were twice those found in rats with unrestricted diets.
The study also found other evidence that brain cell death was at a higher level in the rats with a normal diet.
The lead scientist, Professor Christiaan Leeuwenburgh, said that he had restricted his own calorie intake to a minimum for a decade.
He said that the western lifestyle made it difficult to stick to such harsh regimes.
He said: "We're not going to do it right away to improve our memories - we're going to do it probably in general for the first reasons, which would be to prevent cardiovascular disease and cancer."
However, he said that understanding how these proteins worked might one day offer ways to slow or even halt the advance of diseases which involve the death of brain cells.
The study was published in the journal of the Federation of the American Societies for Experimental Biology.