Effect of caloric restriction on life span of the housefly, Musca domestica

Caloric restriction (CR) has been found to extend the life spans of a wide variety of species, transcending phylogenetic boundaries. The objective of this study was to test the generality of this phenomenon, using the male housefly as an insect model in which food intake can be quantified precisely. Sucrose was found to promote a longer life span than diets additionally containing proteins and lipids. Flies were fed sucrose or a more complex diet ad libitum (AL), or in amounts ranging from 50% to 100% of the average amount consumed by young flies. CR shortened rather than prolonged the life span of houseflies, particularly flies fed sucrose only. The rate of oxygen consumption was not affected by caloric restriction or by the exclusion of proteins and lipids from the diet, and the reproductive activity of male flies remained unchanged by sucrose feeding. Thus, it is unlikely that the life-shortening effects of CR can be explained either in terms of an adaptive response in metabolic rate or use of a suboptimal food source. Results of this study contradict the widely held view that CR has a life-extending effect in all species.