Dietary restriction (DR) is the most robust environmental method of lifespan extension in species as diverse as yeast, worms, fruit flies and rodents. DR is customarily applied by reducing the total amount of food intake, and the individual contribution of each food constituent to the longevity effect remains poorly understood. Our results suggest that both nutritional quality and quantity are critical in determining the normal lifespan of Drosophila melanogaster. We have found that independent variation of both dietary carbohydrate (sucrose, glucose) or yeast extract (protein source) levels have dramatic effects on lifespan. We propose to understand the mechanisms that regulate lifespan upon nutritional manipulation in Drosophila. To this end we will dissect genetic pathways by the use of novel mutants that are sensitive or resistant to various nutritional changes. We propose a comprehensive genetic, biochemical and physiological characterization of how nutritional conditions impact lifespan. There is considerable interest in nutritional interventions that decrease the risk of disease and extend healthy lifespan. Since there is a high degree of genetic homology between humans and model organisms like flies and worms, we believe it is timely to understand the dietary factors that regulate lifespan in these simple organisms. Our findings will have a significant impact on helping to uncover the role of nutrition in the etiology of various age-related human diseases like cancer and diabetes.