WASHINGTON, US - A nutritious but calorie-restricted diet can increase life expectancy and reduce the risk of age-related diseases, including cancer, according to research published in the journal Science Thursday.

The study, conducted over 20 years on dozens of rhesus macaque monkeys, provides new insight into the way the phenomenon works and its potential implications for humans, according to the research authors.

'We have been able to show that caloric restriction can slow the aging process in a primate species,' said Richard Weindruch, a professor of medicine at the University of Wisconsin and an author of the research.

'We observed that caloric restriction reduced the risk of developing an age-related disease by a factor of three and increased survival,' added Weindruch, who led the National Institute on Aging-funded study.

The incidence of cancerous tumors and cardiovascular disease among animals on a calorie-restricted diet was less than half that seen in the control group of monkeys, who were allowed to eat what they wanted.

The study also found that none of the calorie-restricted group suffered from diabetes or glucose impaired regulation, despite the usual frequency of such problems in monkeys.

'So far, we've see the complete prevention of diabetes,' Weindruch said.

Co-author Sterling Johnson, a neuroscientist at the University of Wisconsin, said the caloric reduction also improved brain health.

'It seems to preserve the volume of the brain in some regions,' he said.

'It's not a global effect, but the findings are helping us understand if this dietary treatment is having any effect on the loss of neurons' associated with aging, Johnson said.

Scientists have been interested in the potential for calorie-restricted diets to extend lifespan since the 1930s, when tests were carried out on rats.

Since then, researchers have undertaken studies on calorie reduction on subjects ranging from spiders to humans.