Maintaining a proper diet is not just good for one's body image; it is also good for the brain, according to a new study.

Taking only a restricted number of calories activates a protein which helps the mind stay young and healthy until old age, the study suggests.

The new findings support earlier studies that showed low calorie diets extend the lives of several animals. It also boosts the memory and reduces the risk of dementia, although scientists were not sure how to determine the exact link.

In the new study by Italian scientists, light-calorie diet apparently triggers a protein called CREB1, which in turn stimulates sirtuins, molecules which are associated with longevity.

CREB1 is weakened as humans grow older. Activating CREB1 by eating less could help slow down the mental ageing process, Live Science reports.

The researchers, from the Catholic University of Sacred Heart in Rome, said mice which are only permitted 70 per cent of the calories they would normally eat typically live a third longer than normal and demonstrate better memory and mental function.

Restrictive diet also prevents obesity or diabetes, as well as the onset of dementia.

Mice which were on light diet also showed less aggression.

In contrast having a rich calorie diet is believed to hasten the brain ageing process and raise the risk of age-related diseases like Parkinson's and Alzheimer's.

The new study was published in the Proceedings of the National Academy of Sciences journal.

Dr Giovambattista Pani, who led the research, said: "This discovery has important implications to develop future therapies to keep our brain young and prevent brain degeneration and the ageing process... Our hope is to find a way to activate CREB1, for example through new drugs, so to keep the brain young without the need of a strict diet."