Body weight increment and length of life: the effect of genetic constitution and dietary protein.

Groups of inbred A/J and C57BL/6J mice and hybrid F1 mice were fed low dietary protein (4% casein) or normal dietary protein (26% casein), with 50 mice in each of the six subgroups. For individual mice within subgroups, growth rate was negatively related to longevity; i.e., the slower the rate of growth the greater the life-span. Between subgroups, the longer the mean growth duration, the longer the mean lifespan. Positive relationships were obtained within subgroups for peak body weight and longevity. It is concluded that, for mice, slowing the rate of growth and increasing growth duration results in a significant increase in the life-span, and the life-span increment is not related to high peak body weight since high body weight, per se, was not correlated with life-span.