We already know that in many species, decreasing caloric intake can result in dramatic increases in lifespan. Nonetheless, one would not be tempted to extrapolate the result to the absurd extreme of removing food altogether…unless, apparently, one happens to be a C. elegans, in which it appears that total withdrawal of all food extends adult lifespan, and to a greater extent than calorie restriction (CR). Kaeberlein et al. make the startling report:
A partial reduction in food intake has been found to increase lifespan in many different organisms. We report here a new dietary restriction regimen in the nematode Caenorhabditis elegans, based on the standard agar plate lifespan assay, in which adult worms are maintained in the absence of a bacterial food source. These findings represent the first report in any organism of lifespan extension in response to prolonged starvation. Removal of bacterial food increases lifespan to a greater extent than partial reduction of food through a mechanism that is distinct from insulin/IGF-like signaling and the Sir2-family deacetylase, SIR-2.1. Removal of bacterial food also increases lifespan when initiated in postreproductive adults, suggesting that dietary restriction started during middle age can result in a substantial longevity benefit that is independent of reproduction.
The independence from daf-2/IGF-1 and sirtuin pathways suggests that this lifespan extension is distinct from conventional calorie restriction and is mediated by a genetically novel mechanism that remains to be elucidated — but then again, if you ask the Kaeberlein group, at least some examples of CR life extension are independent of sirtuins anyway, and if that’s true in the worm, then the sirtuin-independence of the full-starvation life extension doesn’t address the point either way.
This result is more than a little stunning. It’s difficult to imagine that it will generalize to larger metazoans: I am pretty sure that complete withdrawal of food from a mouse will dramatically shorten the animal’s lifespan, not extend it. But assuming (1) that this result reproduces in the worm, and (2) that it is indeed mechanistically distinct from conventional CR, one could certainly speculate that the salubrious effects of regular fasting might be mediated by this novel “full withdrawal” pathway rather than by the periodic acute engagement of the CR response.