An interesting paper on one of the many varieties of engineered longevity in mice draws our attention to the links between mitochondrial function and healthy longevity: "Caloric restriction, leanness and decreased activity of insulin/insulin-like growth factor 1 (IGF-1) receptor signaling are associated with increased longevity in a wide range of organisms from Caenorhabditis elegans to humans. Fat-specific insulin receptor knock-out (FIRKO) mice represent an interesting dichotomy, with leanness and increased lifespan, despite normal or increased food intake. ... At the whole body level, FIRKO mice demonstrated an increase in basal metabolic rate and respiratory exchange ratio. Analysis of gene expression [revealed] persistently high expression of the nuclear-encoded mitochondrial genes involved in [the process of energy generation] ... Together, these data suggest that maintenance of mitochondrial activity and metabolic rates in adipose tissue may be important contributors to the increased lifespan of the FIRKO mouse." More evidence that how the machine runs is a lot more important than how fast the machine runs.