This subject has been discussed earlier on this list. I happened
to find some more information on how to interpret the numerous studies
made on mice and rats in the book "Evolution and Healing" that I am
currently reading and from wich I cite:

"Harvard biologist Steven Austad reviewed hundreds of studies of
dietary restriction and found the key in a crucial fact mentioned in
only a few studies. The food-deprived rats may live longer, but they
don't have offspring. In fact, the don't even mate! They seem to
remain at a prereproductive state of development, waiting for an
adequate food supply."

- Hans