Reduced food intake, known as dietary restriction, leads to a longer lifespan in many animals and can improve health in humans. The molecular mechanisms underlying the positive effects of dietary restriction are still unclear. Researchers from the Max Planck Institute for Biology of Ageing have now found one possible explanation in fruit flies: they identified a protein named Sestrin that mediates the beneficial effects of dietary restriction. By increasing the amount of Sestrin in flies, researchers were able to extend their lifespan and at the same time these flies were protected against the lifespan-shortening effects of a protein-rich diet.