3 Calorie Restriction in Lower Organisms

Calorie restriction or dietary restriction is the only known intervention to extend life span in a variety of species including yeast, nematodes, flies, spiders, and mammals (Klass 1977; Weindruch and Walford 1988; Austad 1989; Chippindale et al. 1993; Chapman and Partridge 1996; Lin et al. 2000; Masoro 2005; Tatar 2007). The life span extension seen in each of these species has been reported to be as much as 50%. The fact that such an enormously diverse range of species responds to a reduction in caloric intake by extending their healthy life span highlights the importance of understanding this universal biological phenomenon. Therefore, studying model organisms seems likely to uncover the common underlying mechanistic etiologies for calorie restriction as well as to provide insights into the normal process of aging. This chapter summarizes what has been learned about the molecular genetic mechanisms of calorie restriction (CR) or dietary restriction (DR) and discusses issues specifically related to CR and DR in two of the most frequently used model systems in aging research, the round worm nematode, Caenorhabditis elegans , and the fruit fly, Drosophila melanogaster . CALORIC RESTRICTION OR DIETARY RESTRICTION? The term CR is used to indicate a decrease in total calorie intake unrelated to the specific source of the calories (fat, protein, carbohydrate), whereas DR refers to a decrease in specific nutritional components that need not be accompanied by a decrease in calories. In rats and mice, it has been suggested that it is the total amount of calories, or CR, that...