A study in the journal Science suggests that a strict diet can slow down the ageing process and delay motherhood in Mediterranean fruit flies (medflies).

Lead research Dr James Carey, an insect demographer at the University of California, said it was possible that the findings could lead to a better understanding of how the ageing process works in all animals - including humans.

'Reproduction controls ageing'

Dr Carey said: "The findings suggest that reproduction may be one of the key pacemakers of ageing.

"When food, particularly protein, is in limited supply, female medflies slip into a survival mode, delaying reproduction even until an advanced age.

"But as soon as a complete diet is available, they shift into high gear, producing eggs and ageing rapidly.

"An understanding of the physiological shift that occurs between the waiting and reproductive modes may yield information about the fundamental processes that determines longevity."

Sugar only diet

During the study, Carey and his colleagues compared the fertility and life span of medflies receiving a diet of only sugar to those whose diet was complete with proteins.

Flies deprived of protein went into a "waiting mode" in which both mortality and reproduction were put on hold.

The second group, who had proteins, were actively reproductive and died earlier.

Those flies who were alternately fed and starved of proteins - effectively switching between the two modes - lived the longest of all.

Flies give birth in old age

The research also found that females that were first deprived of protein then fed it at a later age were able to produce eggs at five-months-old - the equivalent of 90-years-old in human terms.

Dr Carey said his research indicated that longevity could probably be achieved by preventing the loss of egg cells, which in humans and other mammals were lost with each ovarian cycle.

He said: "Whereas the reproductive depletion in mammals continues regardless of whether they produce offspring, this loss of reproductive units (potential) does not occur in medflies and other insects unless they actually do produce offspring.

"In short, our findings suggest that non-fertile women such as spinsters and nuns should have no longevity advantage over fertile women.