Figure 1.

Kaplan–Meier plots of survival curves comparing mice of two stocks—CByB6F1/J and UM-HET3 (HET3), a first-generation four-way cross—treated with diet restriction (DR) or ad lib (AL) fed. At the start of the study, each group consisted of 32 mice, 16 of each sex. We initiated DR at 4–5 weeks of age. Treatment was continued until mice died or became moribund. DR increased life span of both stocks and both sexes (p < .0001, likelihood ratio chi-square tests in a proportional hazards model). The relative response to DR was the same for both stocks, and it did not differ between the sexes (no two-way interactions or three-way interaction among stock, sex, and diet in the proportional hazards model). Data were censored for missing mice (see the Methods section) at the following ages (days): two female HET3 AL mice, both at 478 days; two female HET3 DR mice at 987 and 1,292 days; one male CByB6F1 AL mouse at 460 days; two male CByB6F1 DR mice, both at 1,000 days; two male HET3 AL mice at 92 and 477 days; and one male HET3 DR mouse at 932 days. We censored the life span data for one HET3 AL mouse at 266 days due to bite wounds. No data were censored for female CByB6F1 mice. Overall, we censored data for 6 of the 63 AL mice and 5 of the 64 diet-restricted mice.