From The Economist:
It is now generally accepted that eating less makes animals live longer. That has been demonstrated in creatures ranging from worms to mammals. Exactly why it should be so remains, however, hotly debated. So Jeremy Nicholson of Imperial College, London, and his colleagues set out to shed some light on the matter. Their results have just been published in the Journal of Proteome Research.
One theory of ageing suggests senescence is a result of damage caused to body cells by reactive molecules called free radicals. These molecules are created as a side effect of the release of energy from glucose. If that were true, a lower metabolic rate might slow the process down. The question is: does eating less result in a lower metabolic rate? The answer that Dr Nicholson and his colleagues have come up with is that it does—in dogs, at any rate.