A little damage can be a good thing in a self-repairing system: "Oxidative stress has been linked to aging, cancer and other diseases in humans. Paradoxically, researchers have suggested that small exposure to oxidative conditions may actually offer protection from acute doses ... One major contributor to oxidative stress is hydrogen peroxide, converted from a type of free radical that leaks from the mitochondria as it produces energy. ... [Researchers] used the rich functional genomics toolbox of yeast to identify pathways involved in the cell's adaption to hydrogen peroxide. Adaption (or hormesis) is an effect where a toxic substance acts like a stimulant in small doses, but is an inhibitor in large doses. ... This finding may explain recent studies suggesting that eating less may, in fact, raise [oxidant] levels - and, in doing so, provide protection from acute doses of oxidants. This is counter to the hypothesis that caloric restriction extends lifespan in some species because it reduces [oxidants] produced as a by-product of the energy generated by mitochondria. ... It may be that adaption to oxidative stress is the main factor responsible for the lifespan-expanding effects of caloric restriction." Possibly, but my money is still on enhanced autophagy as the major mechanism.