Food restriction is a potent environmental variable and has been shown to increase longevity in diverse organisms, but how food availability affects life span has been unclear. In the January 24 Science, Matthias Blüher and colleagues at Georgetown University, Washington DC, USA, show that a reduction of fat mass without caloric restriction can be associated with increased longevity in mice, possibly through effects on insulin signaling (Science, 299:572-574, January 24, 2003).

Blüher et al. studied fat-specific insulin receptor knockout (FIRKO) mice. They observed that both male and female FIRKO mice had an increase in mean life-span of ~134 days (18%). In addition, these animals had reduced fat mass and were protected against age-related obesity and its subsequent metabolic abnormalities, although their food intake is normal.

These results "are consistent with the view that leanness, not food restriction, is a key contributor to extended longevity. The exact mechanism underlying...

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