A radical theory
Mice that are fed 30 per cent fewer calories live longer. Why? Animals (including you) use oxygen to burn fats and carbohydrates to produce energy. But energy production also makes free radicals - molecules that attack your cells. Most of the time, your cells mop up these free radicals, but this becomes less efficient as you get older. The hungry mice may live longer because they are burning less food, and so making fewer free radicals.